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 // SPDX-License-Identifier: GPL-2.0-or-later
 /*
  *  net/dccp/feat.c
  *
  *  Feature negotiation for the DCCP protocol (RFC 4340, section 6)
  *
  *  Copyright (c) 2008 Gerrit Renker <gerrit@erg.abdn.ac.uk>
  *  Rewrote from scratch, some bits from earlier code by
  *  Copyright (c) 2005 Andrea Bittau <a.bittau@cs.ucl.ac.uk>
  *
  *  ASSUMPTIONS
  *  -----------
  *  o Feature negotiation is coordinated with connection setup (as in TCP), wild
  *    changes of parameters of an established connection are not supported.
  *  o Changing non-negotiable (NN) values is supported in state OPEN/PARTOPEN.
  *  o All currently known SP features have 1-byte quantities. If in the future
  *    extensions of RFCs 4340..42 define features with item lengths larger than
  *    one byte, a feature-specific extension of the code will be required.
  */
 #include <linux/module.h>
 #include <linux/slab.h>
 #include "ccid.h"
 #include "feat.h"
 
 /* feature-specific sysctls - initialised to the defaults from RFC 4340, 6.4 */
 unsigned long   sysctl_dccp_sequence_window __read_mostly = 100;
 int     sysctl_dccp_rx_ccid     __read_mostly = 2,
         sysctl_dccp_tx_ccid     __read_mostly = 2;
 
 /*
  * Feature activation handlers.
  *
  * These all use an u64 argument, to provide enough room for NN/SP features. At
  * this stage the negotiated values have been checked to be within their range.
  */
 static int dccp_hdlr_ccid(struct sock *sk, u64 ccid, bool rx)
 {
     struct dccp_sock *dp = dccp_sk(sk);
     struct ccid *new_ccid = ccid_new(ccid, sk, rx);
 
     if (new_ccid == NULL)
         return -ENOMEM;
 
     if (rx) {
         ccid_hc_rx_delete(dp->dccps_hc_rx_ccid, sk);
         dp->dccps_hc_rx_ccid = new_ccid;
     } else {
         ccid_hc_tx_delete(dp->dccps_hc_tx_ccid, sk);
         dp->dccps_hc_tx_ccid = new_ccid;
     }
     return 0;
 }
 
 static int dccp_hdlr_seq_win(struct sock *sk, u64 seq_win, bool rx)
 {
     struct dccp_sock *dp = dccp_sk(sk);
 
     if (rx) {
         dp->dccps_r_seq_win = seq_win;
         /* propagate changes to update SWL/SWH */
         dccp_update_gsr(sk, dp->dccps_gsr);
     } else {
         dp->dccps_l_seq_win = seq_win;
         /* propagate changes to update AWL */
         dccp_update_gss(sk, dp->dccps_gss);
     }
     return 0;
 }
 
 static int dccp_hdlr_ack_ratio(struct sock *sk, u64 ratio, bool rx)
 {
     if (rx)
         dccp_sk(sk)->dccps_r_ack_ratio = ratio;
     else
         dccp_sk(sk)->dccps_l_ack_ratio = ratio;
     return 0;
 }
 
 static int dccp_hdlr_ackvec(struct sock *sk, u64 enable, bool rx)
 {
     struct dccp_sock *dp = dccp_sk(sk);
 
     if (rx) {
         if (enable && dp->dccps_hc_rx_ackvec == NULL) {
             dp->dccps_hc_rx_ackvec = dccp_ackvec_alloc(gfp_any());
             if (dp->dccps_hc_rx_ackvec == NULL)
                 return -ENOMEM;
         } else if (!enable) {
             dccp_ackvec_free(dp->dccps_hc_rx_ackvec);
             dp->dccps_hc_rx_ackvec = NULL;
         }
     }
     return 0;
 }
 
 static int dccp_hdlr_ndp(struct sock *sk, u64 enable, bool rx)
 {
     if (!rx)
         dccp_sk(sk)->dccps_send_ndp_count = (enable > 0);
     return 0;
 }
 
 /*
  * Minimum Checksum Coverage is located at the RX side (9.2.1). This means that
  * `rx' holds when the sending peer informs about his partial coverage via a
  * ChangeR() option. In the other case, we are the sender and the receiver
  * announces its coverage via ChangeL() options. The policy here is to honour
  * such communication by enabling the corresponding partial coverage - but only
  * if it has not been set manually before; the warning here means that all
  * packets will be dropped.
  */
 static int dccp_hdlr_min_cscov(struct sock *sk, u64 cscov, bool rx)
 {
     struct dccp_sock *dp = dccp_sk(sk);
 
     if (rx)
         dp->dccps_pcrlen = cscov;
     else {
         if (dp->dccps_pcslen == 0)
             dp->dccps_pcslen = cscov;
         else if (cscov > dp->dccps_pcslen)
             DCCP_WARN("CsCov %u too small, peer requires >= %u\n",
                   dp->dccps_pcslen, (u8)cscov);
     }
     return 0;
 }
 
 static const struct {
     u8          feat_num;       /* DCCPF_xxx */
     enum dccp_feat_type rxtx;           /* RX or TX  */
     enum dccp_feat_type reconciliation;     /* SP or NN  */
     u8          default_value;      /* as in 6.4 */
     int (*activation_hdlr)(struct sock *sk, u64 val, bool rx);
 /*
  *    Lookup table for location and type of features (from RFC 4340/4342)
  *  +--------------------------+----+-----+----+----+---------+-----------+
  *  | Feature                  | Location | Reconc. | Initial |  Section  |
  *  |                          | RX | TX  | SP | NN |  Value  | Reference |
  *  +--------------------------+----+-----+----+----+---------+-----------+
  *  | DCCPF_CCID               |    |  X  | X  |    |   2     | 10        |
  *  | DCCPF_SHORT_SEQNOS       |    |  X  | X  |    |   0     |  7.6.1    |
  *  | DCCPF_SEQUENCE_WINDOW    |    |  X  |    | X  | 100     |  7.5.2    |
  *  | DCCPF_ECN_INCAPABLE      | X  |     | X  |    |   0     | 12.1      |
  *  | DCCPF_ACK_RATIO          |    |  X  |    | X  |   2     | 11.3      |
  *  | DCCPF_SEND_ACK_VECTOR    | X  |     | X  |    |   0     | 11.5      |
  *  | DCCPF_SEND_NDP_COUNT     |    |  X  | X  |    |   0     |  7.7.2    |
  *  | DCCPF_MIN_CSUM_COVER     | X  |     | X  |    |   0     |  9.2.1    |
  *  | DCCPF_DATA_CHECKSUM      | X  |     | X  |    |   0     |  9.3.1    |
  *  | DCCPF_SEND_LEV_RATE      | X  |     | X  |    |   0     | 4342/8.4  |
  *  +--------------------------+----+-----+----+----+---------+-----------+
  */
 } dccp_feat_table[] = {
     { DCCPF_CCID,        FEAT_AT_TX, FEAT_SP, 2,   dccp_hdlr_ccid     },
     { DCCPF_SHORT_SEQNOS,    FEAT_AT_TX, FEAT_SP, 0,   NULL },
     { DCCPF_SEQUENCE_WINDOW, FEAT_AT_TX, FEAT_NN, 100, dccp_hdlr_seq_win  },
     { DCCPF_ECN_INCAPABLE,   FEAT_AT_RX, FEAT_SP, 0,   NULL },
     { DCCPF_ACK_RATIO,   FEAT_AT_TX, FEAT_NN, 2,   dccp_hdlr_ack_ratio},
     { DCCPF_SEND_ACK_VECTOR, FEAT_AT_RX, FEAT_SP, 0,   dccp_hdlr_ackvec   },
     { DCCPF_SEND_NDP_COUNT,  FEAT_AT_TX, FEAT_SP, 0,   dccp_hdlr_ndp      },
     { DCCPF_MIN_CSUM_COVER,  FEAT_AT_RX, FEAT_SP, 0,   dccp_hdlr_min_cscov},
     { DCCPF_DATA_CHECKSUM,   FEAT_AT_RX, FEAT_SP, 0,   NULL },
     { DCCPF_SEND_LEV_RATE,   FEAT_AT_RX, FEAT_SP, 0,   NULL },
 };
 #define DCCP_FEAT_SUPPORTED_MAX     ARRAY_SIZE(dccp_feat_table)
 
 /**
  * dccp_feat_index  -  Hash function to map feature number into array position
  * @feat_num: feature to hash, one of %dccp_feature_numbers
  *
  * Returns consecutive array index or -1 if the feature is not understood.
  */
 static int dccp_feat_index(u8 feat_num)
 {
     /* The first 9 entries are occupied by the types from RFC 4340, 6.4 */
     if (feat_num > DCCPF_RESERVED && feat_num <= DCCPF_DATA_CHECKSUM)
         return feat_num - 1;
 
     /*
      * Other features: add cases for new feature types here after adding
      * them to the above table.
      */
     switch (feat_num) {
     case DCCPF_SEND_LEV_RATE:
             return DCCP_FEAT_SUPPORTED_MAX - 1;
     }
     return -1;
 }
 
 static u8 dccp_feat_type(u8 feat_num)
 {
     int idx = dccp_feat_index(feat_num);
 
     if (idx < 0)
         return FEAT_UNKNOWN;
     return dccp_feat_table[idx].reconciliation;
 }
 
 static int dccp_feat_default_value(u8 feat_num)
 {
     int idx = dccp_feat_index(feat_num);
     /*
      * There are no default values for unknown features, so encountering a
      * negative index here indicates a serious problem somewhere else.
      */
     DCCP_BUG_ON(idx < 0);
 
     return idx < 0 ? 0 : dccp_feat_table[idx].default_value;
 }
 
 /*
  *  Debugging and verbose-printing section
  */
 static const char *dccp_feat_fname(const u8 feat)
 {
     static const char *const feature_names[] = {
         [DCCPF_RESERVED]    = "Reserved",
         [DCCPF_CCID]        = "CCID",
         [DCCPF_SHORT_SEQNOS]    = "Allow Short Seqnos",
         [DCCPF_SEQUENCE_WINDOW] = "Sequence Window",
         [DCCPF_ECN_INCAPABLE]   = "ECN Incapable",
         [DCCPF_ACK_RATIO]   = "Ack Ratio",
         [DCCPF_SEND_ACK_VECTOR] = "Send ACK Vector",
         [DCCPF_SEND_NDP_COUNT]  = "Send NDP Count",
         [DCCPF_MIN_CSUM_COVER]  = "Min. Csum Coverage",
         [DCCPF_DATA_CHECKSUM]   = "Send Data Checksum",
     };
     if (feat > DCCPF_DATA_CHECKSUM && feat < DCCPF_MIN_CCID_SPECIFIC)
         return feature_names[DCCPF_RESERVED];
 
     if (feat ==  DCCPF_SEND_LEV_RATE)
         return "Send Loss Event Rate";
     if (feat >= DCCPF_MIN_CCID_SPECIFIC)
         return "CCID-specific";
 
     return feature_names[feat];
 }
 
 static const char *const dccp_feat_sname[] = {
     "DEFAULT", "INITIALISING", "CHANGING", "UNSTABLE", "STABLE",
 };
 
 #ifdef CONFIG_IP_DCCP_DEBUG
 static const char *dccp_feat_oname(const u8 opt)
 {
     switch (opt) {
     case DCCPO_CHANGE_L:  return "Change_L";
     case DCCPO_CONFIRM_L: return "Confirm_L";
     case DCCPO_CHANGE_R:  return "Change_R";
     case DCCPO_CONFIRM_R: return "Confirm_R";
     }
     return NULL;
 }
 
 static void dccp_feat_printval(u8 feat_num, dccp_feat_val const *val)
 {
     u8 i, type = dccp_feat_type(feat_num);
 
     if (val == NULL || (type == FEAT_SP && val->sp.vec == NULL))
         dccp_pr_debug_cat("(NULL)");
     else if (type == FEAT_SP)
         for (i = 0; i < val->sp.len; i++)
             dccp_pr_debug_cat("%s%u", i ? " " : "", val->sp.vec[i]);
     else if (type == FEAT_NN)
         dccp_pr_debug_cat("%llu", (unsigned long long)val->nn);
     else
         dccp_pr_debug_cat("unknown type %u", type);
 }
 
 static void dccp_feat_printvals(u8 feat_num, u8 *list, u8 len)
 {
     u8 type = dccp_feat_type(feat_num);
     dccp_feat_val fval = { .sp.vec = list, .sp.len = len };
 
     if (type == FEAT_NN)
         fval.nn = dccp_decode_value_var(list, len);
     dccp_feat_printval(feat_num, &fval);
 }
 
 static void dccp_feat_print_entry(struct dccp_feat_entry const *entry)
 {
     dccp_debug("   * %s %s = ", entry->is_local ? "local" : "remote",
                     dccp_feat_fname(entry->feat_num));
     dccp_feat_printval(entry->feat_num, &entry->val);
     dccp_pr_debug_cat(", state=%s %s\n", dccp_feat_sname[entry->state],
               entry->needs_confirm ? "(Confirm pending)" : "");
 }
 
 #define dccp_feat_print_opt(opt, feat, val, len, mandatory) do {          \
     dccp_pr_debug("%s(%s, ", dccp_feat_oname(opt), dccp_feat_fname(feat));\
     dccp_feat_printvals(feat, val, len);                      \
     dccp_pr_debug_cat(") %s\n", mandatory ? "!" : "");  } while (0)
 
 #define dccp_feat_print_fnlist(fn_list)  {      \
     const struct dccp_feat_entry *___entry;     \
                             \
     dccp_pr_debug("List Dump:\n");          \
     list_for_each_entry(___entry, fn_list, node)    \
         dccp_feat_print_entry(___entry);    \
 }
 #else   /* ! CONFIG_IP_DCCP_DEBUG */
 #define dccp_feat_print_opt(opt, feat, val, len, mandatory)
 #define dccp_feat_print_fnlist(fn_list)
 #endif
 
 static int __dccp_feat_activate(struct sock *sk, const int idx,
                 const bool is_local, dccp_feat_val const *fval)
 {
     bool rx;
     u64 val;
 
     if (idx < 0 || idx >= DCCP_FEAT_SUPPORTED_MAX)
         return -1;
     if (dccp_feat_table[idx].activation_hdlr == NULL)
         return 0;
 
     if (fval == NULL) {
         val = dccp_feat_table[idx].default_value;
     } else if (dccp_feat_table[idx].reconciliation == FEAT_SP) {
         if (fval->sp.vec == NULL) {
             /*
              * This can happen when an empty Confirm is sent
              * for an SP (i.e. known) feature. In this case
              * we would be using the default anyway.
              */
             DCCP_CRIT("Feature #%d undefined: using default", idx);
             val = dccp_feat_table[idx].default_value;
         } else {
             val = fval->sp.vec[0];
         }
     } else {
         val = fval->nn;
     }
 
     /* Location is RX if this is a local-RX or remote-TX feature */
     rx = (is_local == (dccp_feat_table[idx].rxtx == FEAT_AT_RX));
 
     dccp_debug("   -> activating %s %s, %sval=%llu\n", rx ? "RX" : "TX",
            dccp_feat_fname(dccp_feat_table[idx].feat_num),
            fval ? "" : "default ",  (unsigned long long)val);
 
     return dccp_feat_table[idx].activation_hdlr(sk, val, rx);
 }
 
 /**
  * dccp_feat_activate  -  Activate feature value on socket
  * @sk: fully connected DCCP socket (after handshake is complete)
  * @feat_num: feature to activate, one of %dccp_feature_numbers
  * @local: whether local (1) or remote (0) @feat_num is meant
  * @fval: the value (SP or NN) to activate, or NULL to use the default value
  *
  * For general use this function is preferable over __dccp_feat_activate().
  */
 static int dccp_feat_activate(struct sock *sk, u8 feat_num, bool local,
                   dccp_feat_val const *fval)
 {
     return __dccp_feat_activate(sk, dccp_feat_index(feat_num), local, fval);
 }
 
 /* Test for "Req'd" feature (RFC 4340, 6.4) */
 static inline int dccp_feat_must_be_understood(u8 feat_num)
 {
     return  feat_num == DCCPF_CCID || feat_num == DCCPF_SHORT_SEQNOS ||
         feat_num == DCCPF_SEQUENCE_WINDOW;
 }
 
 /* copy constructor, fval must not already contain allocated memory */
 static int dccp_feat_clone_sp_val(dccp_feat_val *fval, u8 const *val, u8 len)
 {
     fval->sp.len = len;
     if (fval->sp.len > 0) {
         fval->sp.vec = kmemdup(val, len, gfp_any());
         if (fval->sp.vec == NULL) {
             fval->sp.len = 0;
             return -ENOMEM;
         }
     }
     return 0;
 }
 
 static void dccp_feat_val_destructor(u8 feat_num, dccp_feat_val *val)
 {
     if (unlikely(val == NULL))
         return;
     if (dccp_feat_type(feat_num) == FEAT_SP)
         kfree(val->sp.vec);
     memset(val, 0, sizeof(*val));
 }
 
 static struct dccp_feat_entry *
           dccp_feat_clone_entry(struct dccp_feat_entry const *original)
 {
     struct dccp_feat_entry *new;
     u8 type = dccp_feat_type(original->feat_num);
 
     if (type == FEAT_UNKNOWN)
         return NULL;
 
     new = kmemdup(original, sizeof(struct dccp_feat_entry), gfp_any());
     if (new == NULL)
         return NULL;
 
     if (type == FEAT_SP && dccp_feat_clone_sp_val(&new->val,
                               original->val.sp.vec,
                               original->val.sp.len)) {
         kfree(new);
         return NULL;
     }
     return new;
 }
 
 static void dccp_feat_entry_destructor(struct dccp_feat_entry *entry)
 {
     if (entry != NULL) {
         dccp_feat_val_destructor(entry->feat_num, &entry->val);
         kfree(entry);
     }
 }
 
 /*
  * List management functions
  *
  * Feature negotiation lists rely on and maintain the following invariants:
  * - each feat_num in the list is known, i.e. we know its type and default value
  * - each feat_num/is_local combination is unique (old entries are overwritten)
  * - SP values are always freshly allocated
  * - list is sorted in increasing order of feature number (faster lookup)
  */
 static struct dccp_feat_entry *dccp_feat_list_lookup(struct list_head *fn_list,
                              u8 feat_num, bool is_local)
 {
     struct dccp_feat_entry *entry;
 
     list_for_each_entry(entry, fn_list, node) {
         if (entry->feat_num == feat_num && entry->is_local == is_local)
             return entry;
         else if (entry->feat_num > feat_num)
             break;
     }
     return NULL;
 }
 
 /**
  * dccp_feat_entry_new  -  Central list update routine (called by all others)
  * @head:  list to add to
  * @feat:  feature number
  * @local: whether the local (1) or remote feature with number @feat is meant
  *
  * This is the only constructor and serves to ensure the above invariants.
  */
 static struct dccp_feat_entry *
           dccp_feat_entry_new(struct list_head *head, u8 feat, bool local)
 {
     struct dccp_feat_entry *entry;
 
     list_for_each_entry(entry, head, node)
         if (entry->feat_num == feat && entry->is_local == local) {
             dccp_feat_val_destructor(entry->feat_num, &entry->val);
             return entry;
         } else if (entry->feat_num > feat) {
             head = &entry->node;
             break;
         }
 
     entry = kmalloc(sizeof(*entry), gfp_any());
     if (entry != NULL) {
         entry->feat_num = feat;
         entry->is_local = local;
         list_add_tail(&entry->node, head);
     }
     return entry;
 }
 
 /**
  * dccp_feat_push_change  -  Add/overwrite a Change option in the list
  * @fn_list: feature-negotiation list to update
  * @feat: one of %dccp_feature_numbers
  * @local: whether local (1) or remote (0) @feat_num is meant
  * @mandatory: whether to use Mandatory feature negotiation options
  * @fval: pointer to NN/SP value to be inserted (will be copied)
  */
 static int dccp_feat_push_change(struct list_head *fn_list, u8 feat, u8 local,
                  u8 mandatory, dccp_feat_val *fval)
 {
     struct dccp_feat_entry *new = dccp_feat_entry_new(fn_list, feat, local);
 
     if (new == NULL)
         return -ENOMEM;
 
     new->feat_num        = feat;
     new->is_local        = local;
     new->state       = FEAT_INITIALISING;
     new->needs_confirm   = false;
     new->empty_confirm   = false;
     new->val         = *fval;
     new->needs_mandatory = mandatory;
 
     return 0;
 }
 
 /**
  * dccp_feat_push_confirm  -  Add a Confirm entry to the FN list
  * @fn_list: feature-negotiation list to add to
  * @feat: one of %dccp_feature_numbers
  * @local: whether local (1) or remote (0) @feat_num is being confirmed
  * @fval: pointer to NN/SP value to be inserted or NULL
  *
  * Returns 0 on success, a Reset code for further processing otherwise.
  */
 static int dccp_feat_push_confirm(struct list_head *fn_list, u8 feat, u8 local,
                   dccp_feat_val *fval)
 {
     struct dccp_feat_entry *new = dccp_feat_entry_new(fn_list, feat, local);
 
     if (new == NULL)
         return DCCP_RESET_CODE_TOO_BUSY;
 
     new->feat_num        = feat;
     new->is_local        = local;
     new->state       = FEAT_STABLE; /* transition in 6.6.2 */
     new->needs_confirm   = true;
     new->empty_confirm   = (fval == NULL);
     new->val.nn      = 0;       /* zeroes the whole structure */
     if (!new->empty_confirm)
         new->val     = *fval;
     new->needs_mandatory = false;
 
     return 0;
 }
 
 static int dccp_push_empty_confirm(struct list_head *fn_list, u8 feat, u8 local)
 {
     return dccp_feat_push_confirm(fn_list, feat, local, NULL);
 }
 
 static inline void dccp_feat_list_pop(struct dccp_feat_entry *entry)
 {
     list_del(&entry->node);
     dccp_feat_entry_destructor(entry);
 }
 
 void dccp_feat_list_purge(struct list_head *fn_list)
 {
     struct dccp_feat_entry *entry, *next;
 
     list_for_each_entry_safe(entry, next, fn_list, node)
         dccp_feat_entry_destructor(entry);
     INIT_LIST_HEAD(fn_list);
 }
 EXPORT_SYMBOL_GPL(dccp_feat_list_purge);
 
 /* generate @to as full clone of @from - @to must not contain any nodes */
 int dccp_feat_clone_list(struct list_head const *from, struct list_head *to)
 {
     struct dccp_feat_entry *entry, *new;
 
     INIT_LIST_HEAD(to);
     list_for_each_entry(entry, from, node) {
         new = dccp_feat_clone_entry(entry);
         if (new == NULL)
             goto cloning_failed;
         list_add_tail(&new->node, to);
     }
     return 0;
 
 cloning_failed:
     dccp_feat_list_purge(to);
     return -ENOMEM;
 }
 
 /**
  * dccp_feat_valid_nn_length  -  Enforce length constraints on NN options
  * @feat_num: feature to return length of, one of %dccp_feature_numbers
  *
  * Length is between 0 and %DCCP_OPTVAL_MAXLEN. Used for outgoing packets only,
  * incoming options are accepted as long as their values are valid.
  */
 static u8 dccp_feat_valid_nn_length(u8 feat_num)
 {
     if (feat_num == DCCPF_ACK_RATIO)    /* RFC 4340, 11.3 and 6.6.8 */
         return 2;
     if (feat_num == DCCPF_SEQUENCE_WINDOW)  /* RFC 4340, 7.5.2 and 6.5  */
         return 6;
     return 0;
 }
 
 static u8 dccp_feat_is_valid_nn_val(u8 feat_num, u64 val)
 {
     switch (feat_num) {
     case DCCPF_ACK_RATIO:
         return val <= DCCPF_ACK_RATIO_MAX;
     case DCCPF_SEQUENCE_WINDOW:
         return val >= DCCPF_SEQ_WMIN && val <= DCCPF_SEQ_WMAX;
     }
     return 0;   /* feature unknown - so we can't tell */
 }
 
 /* check that SP values are within the ranges defined in RFC 4340 */
 static u8 dccp_feat_is_valid_sp_val(u8 feat_num, u8 val)
 {
     switch (feat_num) {
     case DCCPF_CCID:
         return val == DCCPC_CCID2 || val == DCCPC_CCID3;
     /* Type-check Boolean feature values: */
     case DCCPF_SHORT_SEQNOS:
     case DCCPF_ECN_INCAPABLE:
     case DCCPF_SEND_ACK_VECTOR:
     case DCCPF_SEND_NDP_COUNT:
     case DCCPF_DATA_CHECKSUM:
     case DCCPF_SEND_LEV_RATE:
         return val < 2;
     case DCCPF_MIN_CSUM_COVER:
         return val < 16;
     }
     return 0;           /* feature unknown */
 }
 
 static u8 dccp_feat_sp_list_ok(u8 feat_num, u8 const *sp_list, u8 sp_len)
 {
     if (sp_list == NULL || sp_len < 1)
         return 0;
     while (sp_len--)
         if (!dccp_feat_is_valid_sp_val(feat_num, *sp_list++))
             return 0;
     return 1;
 }
 
 /**
  * dccp_feat_insert_opts  -  Generate FN options from current list state
  * @skb: next sk_buff to be sent to the peer
  * @dp: for client during handshake and general negotiation
  * @dreq: used by the server only (all Changes/Confirms in LISTEN/RESPOND)
  */
 int dccp_feat_insert_opts(struct dccp_sock *dp, struct dccp_request_sock *dreq,
               struct sk_buff *skb)
 {
     struct list_head *fn = dreq ? &dreq->dreq_featneg : &dp->dccps_featneg;
     struct dccp_feat_entry *pos, *next;
     u8 opt, type, len, *ptr, nn_in_nbo[DCCP_OPTVAL_MAXLEN];
     bool rpt;
 
     /* put entries into @skb in the order they appear in the list */
     list_for_each_entry_safe_reverse(pos, next, fn, node) {
         opt  = dccp_feat_genopt(pos);
         type = dccp_feat_type(pos->feat_num);
         rpt  = false;
 
         if (pos->empty_confirm) {
             len = 0;
             ptr = NULL;
         } else {
             if (type == FEAT_SP) {
                 len = pos->val.sp.len;
                 ptr = pos->val.sp.vec;
                 rpt = pos->needs_confirm;
             } else if (type == FEAT_NN) {
                 len = dccp_feat_valid_nn_length(pos->feat_num);
                 ptr = nn_in_nbo;
                 dccp_encode_value_var(pos->val.nn, ptr, len);
             } else {
                 DCCP_BUG("unknown feature %u", pos->feat_num);
                 return -1;
             }
         }
         dccp_feat_print_opt(opt, pos->feat_num, ptr, len, 0);
 
         if (dccp_insert_fn_opt(skb, opt, pos->feat_num, ptr, len, rpt))
             return -1;
         if (pos->needs_mandatory && dccp_insert_option_mandatory(skb))
             return -1;
 
         if (skb->sk->sk_state == DCCP_OPEN &&
             (opt == DCCPO_CONFIRM_R || opt == DCCPO_CONFIRM_L)) {
             /*
              * Confirms don't get retransmitted (6.6.3) once the
              * connection is in state OPEN
              */
             dccp_feat_list_pop(pos);
         } else {
             /*
              * Enter CHANGING after transmitting the Change
              * option (6.6.2).
              */
             if (pos->state == FEAT_INITIALISING)
                 pos->state = FEAT_CHANGING;
         }
     }
     return 0;
 }
 
 /**
  * __feat_register_nn  -  Register new NN value on socket
  * @fn: feature-negotiation list to register with
  * @feat: an NN feature from %dccp_feature_numbers
  * @mandatory: use Mandatory option if 1
  * @nn_val: value to register (restricted to 4 bytes)
  *
  * Note that NN features are local by definition (RFC 4340, 6.3.2).
  */
 static int __feat_register_nn(struct list_head *fn, u8 feat,
                   u8 mandatory, u64 nn_val)
 {
     dccp_feat_val fval = { .nn = nn_val };
 
     if (dccp_feat_type(feat) != FEAT_NN ||
         !dccp_feat_is_valid_nn_val(feat, nn_val))
         return -EINVAL;
 
     /* Don't bother with default values, they will be activated anyway. */
     if (nn_val - (u64)dccp_feat_default_value(feat) == 0)
         return 0;
 
     return dccp_feat_push_change(fn, feat, 1, mandatory, &fval);
 }
 
 /**
  * __feat_register_sp  -  Register new SP value/list on socket
  * @fn: feature-negotiation list to register with
  * @feat: an SP feature from %dccp_feature_numbers
  * @is_local: whether the local (1) or the remote (0) @feat is meant
  * @mandatory: use Mandatory option if 1
  * @sp_val: SP value followed by optional preference list
  * @sp_len: length of @sp_val in bytes
  */
 static int __feat_register_sp(struct list_head *fn, u8 feat, u8 is_local,
                   u8 mandatory, u8 const *sp_val, u8 sp_len)
 {
     dccp_feat_val fval;
 
     if (dccp_feat_type(feat) != FEAT_SP ||
         !dccp_feat_sp_list_ok(feat, sp_val, sp_len))
         return -EINVAL;
 
     /* Avoid negotiating alien CCIDs by only advertising supported ones */
     if (feat == DCCPF_CCID && !ccid_support_check(sp_val, sp_len))
         return -EOPNOTSUPP;
 
     if (dccp_feat_clone_sp_val(&fval, sp_val, sp_len))
         return -ENOMEM;
 
     if (dccp_feat_push_change(fn, feat, is_local, mandatory, &fval)) {
         kfree(fval.sp.vec);
         return -ENOMEM;
     }
 
     return 0;
 }
 
 /**
  * dccp_feat_register_sp  -  Register requests to change SP feature values
  * @sk: client or listening socket
  * @feat: one of %dccp_feature_numbers
  * @is_local: whether the local (1) or remote (0) @feat is meant
  * @list: array of preferred values, in descending order of preference
  * @len: length of @list in bytes
  */
 int dccp_feat_register_sp(struct sock *sk, u8 feat, u8 is_local,
               u8 const *list, u8 len)
 {    /* any changes must be registered before establishing the connection */
     if (sk->sk_state != DCCP_CLOSED)
         return -EISCONN;
     if (dccp_feat_type(feat) != FEAT_SP)
         return -EINVAL;
     return __feat_register_sp(&dccp_sk(sk)->dccps_featneg, feat, is_local,
                   0, list, len);
 }
 
 /**
  * dccp_feat_nn_get  -  Query current/pending value of NN feature
  * @sk: DCCP socket of an established connection
  * @feat: NN feature number from %dccp_feature_numbers
  *
  * For a known NN feature, returns value currently being negotiated, or
  * current (confirmed) value if no negotiation is going on.
  */
 u64 dccp_feat_nn_get(struct sock *sk, u8 feat)
 {
     if (dccp_feat_type(feat) == FEAT_NN) {
         struct dccp_sock *dp = dccp_sk(sk);
         struct dccp_feat_entry *entry;
 
         entry = dccp_feat_list_lookup(&dp->dccps_featneg, feat, 1);
         if (entry != NULL)
             return entry->val.nn;
 
         switch (feat) {
         case DCCPF_ACK_RATIO:
             return dp->dccps_l_ack_ratio;
         case DCCPF_SEQUENCE_WINDOW:
             return dp->dccps_l_seq_win;
         }
     }
     DCCP_BUG("attempt to look up unsupported feature %u", feat);
     return 0;
 }
 EXPORT_SYMBOL_GPL(dccp_feat_nn_get);
 
 /**
  * dccp_feat_signal_nn_change  -  Update NN values for an established connection
  * @sk: DCCP socket of an established connection
  * @feat: NN feature number from %dccp_feature_numbers
  * @nn_val: the new value to use
  *
  * This function is used to communicate NN updates out-of-band.
  */
 int dccp_feat_signal_nn_change(struct sock *sk, u8 feat, u64 nn_val)
 {
     struct list_head *fn = &dccp_sk(sk)->dccps_featneg;
     dccp_feat_val fval = { .nn = nn_val };
     struct dccp_feat_entry *entry;
 
     if (sk->sk_state != DCCP_OPEN && sk->sk_state != DCCP_PARTOPEN)
         return 0;
 
     if (dccp_feat_type(feat) != FEAT_NN ||
         !dccp_feat_is_valid_nn_val(feat, nn_val))
         return -EINVAL;
 
     if (nn_val == dccp_feat_nn_get(sk, feat))
         return 0;   /* already set or negotiation under way */
 
     entry = dccp_feat_list_lookup(fn, feat, 1);
     if (entry != NULL) {
         dccp_pr_debug("Clobbering existing NN entry %llu -> %llu\n",
                   (unsigned long long)entry->val.nn,
                   (unsigned long long)nn_val);
         dccp_feat_list_pop(entry);
     }
 
     inet_csk_schedule_ack(sk);
     return dccp_feat_push_change(fn, feat, 1, 0, &fval);
 }
 EXPORT_SYMBOL_GPL(dccp_feat_signal_nn_change);
 
 /*
  *  Tracking features whose value depend on the choice of CCID
  *
  * This is designed with an extension in mind so that a list walk could be done
  * before activating any features. However, the existing framework was found to
  * work satisfactorily up until now, the automatic verification is left open.
  * When adding new CCIDs, add a corresponding dependency table here.
  */
 static const struct ccid_dependency *dccp_feat_ccid_deps(u8 ccid, bool is_local)
 {
     static const struct ccid_dependency ccid2_dependencies[2][2] = {
         /*
          * CCID2 mandates Ack Vectors (RFC 4341, 4.): as CCID is a TX
          * feature and Send Ack Vector is an RX feature, `is_local'
          * needs to be reversed.
          */
         {   /* Dependencies of the receiver-side (remote) CCID2 */
             {
                 .dependent_feat = DCCPF_SEND_ACK_VECTOR,
                 .is_local   = true,
                 .is_mandatory   = true,
                 .val        = 1
             },
             { 0, 0, 0, 0 }
         },
         {   /* Dependencies of the sender-side (local) CCID2 */
             {
                 .dependent_feat = DCCPF_SEND_ACK_VECTOR,
                 .is_local   = false,
                 .is_mandatory   = true,
                 .val        = 1
             },
             { 0, 0, 0, 0 }
         }
     };
     static const struct ccid_dependency ccid3_dependencies[2][5] = {
         {   /*
              * Dependencies of the receiver-side CCID3
              */
             {   /* locally disable Ack Vectors */
                 .dependent_feat = DCCPF_SEND_ACK_VECTOR,
                 .is_local   = true,
                 .is_mandatory   = false,
                 .val        = 0
             },
             {   /* see below why Send Loss Event Rate is on */
                 .dependent_feat = DCCPF_SEND_LEV_RATE,
                 .is_local   = true,
                 .is_mandatory   = true,
                 .val        = 1
             },
             {   /* NDP Count is needed as per RFC 4342, 6.1.1 */
                 .dependent_feat = DCCPF_SEND_NDP_COUNT,
                 .is_local   = false,
                 .is_mandatory   = true,
                 .val        = 1
             },
             { 0, 0, 0, 0 },
         },
         {   /*
              * CCID3 at the TX side: we request that the HC-receiver
              * will not send Ack Vectors (they will be ignored, so
              * Mandatory is not set); we enable Send Loss Event Rate
              * (Mandatory since the implementation does not support
              * the Loss Intervals option of RFC 4342, 8.6).
              * The last two options are for peer's information only.
             */
             {
                 .dependent_feat = DCCPF_SEND_ACK_VECTOR,
                 .is_local   = false,
                 .is_mandatory   = false,
                 .val        = 0
             },
             {
                 .dependent_feat = DCCPF_SEND_LEV_RATE,
                 .is_local   = false,
                 .is_mandatory   = true,
                 .val        = 1
             },
             {   /* this CCID does not support Ack Ratio */
                 .dependent_feat = DCCPF_ACK_RATIO,
                 .is_local   = true,
                 .is_mandatory   = false,
                 .val        = 0
             },
             {   /* tell receiver we are sending NDP counts */
                 .dependent_feat = DCCPF_SEND_NDP_COUNT,
                 .is_local   = true,
                 .is_mandatory   = false,
                 .val        = 1
             },
             { 0, 0, 0, 0 }
         }
     };
     switch (ccid) {
     case DCCPC_CCID2:
         return ccid2_dependencies[is_local];
     case DCCPC_CCID3:
         return ccid3_dependencies[is_local];
     default:
         return NULL;
     }
 }
 
 /**
  * dccp_feat_propagate_ccid - Resolve dependencies of features on choice of CCID
  * @fn: feature-negotiation list to update
  * @id: CCID number to track
  * @is_local: whether TX CCID (1) or RX CCID (0) is meant
  *
  * This function needs to be called after registering all other features.
  */
 static int dccp_feat_propagate_ccid(struct list_head *fn, u8 id, bool is_local)
 {
     const struct ccid_dependency *table = dccp_feat_ccid_deps(id, is_local);
     int i, rc = (table == NULL);
 
     for (i = 0; rc == 0 && table[i].dependent_feat != DCCPF_RESERVED; i++)
         if (dccp_feat_type(table[i].dependent_feat) == FEAT_SP)
             rc = __feat_register_sp(fn, table[i].dependent_feat,
                             table[i].is_local,
                             table[i].is_mandatory,
                             &table[i].val, 1);
         else
             rc = __feat_register_nn(fn, table[i].dependent_feat,
                             table[i].is_mandatory,
                             table[i].val);
     return rc;
 }
 
 /**
  * dccp_feat_finalise_settings  -  Finalise settings before starting negotiation
  * @dp: client or listening socket (settings will be inherited)
  *
  * This is called after all registrations (socket initialisation, sysctls, and
  * sockopt calls), and before sending the first packet containing Change options
  * (ie. client-Request or server-Response), to ensure internal consistency.
  */
 int dccp_feat_finalise_settings(struct dccp_sock *dp)
 {
     struct list_head *fn = &dp->dccps_featneg;
     struct dccp_feat_entry *entry;
     int i = 2, ccids[2] = { -1, -1 };
 
     /*
      * Propagating CCIDs:
      * 1) not useful to propagate CCID settings if this host advertises more
      *    than one CCID: the choice of CCID  may still change - if this is
      *    the client, or if this is the server and the client sends
      *    singleton CCID values.
      * 2) since is that propagate_ccid changes the list, we defer changing
      *    the sorted list until after the traversal.
      */
     list_for_each_entry(entry, fn, node)
         if (entry->feat_num == DCCPF_CCID && entry->val.sp.len == 1)
             ccids[entry->is_local] = entry->val.sp.vec[0];
     while (i--)
         if (ccids[i] > 0 && dccp_feat_propagate_ccid(fn, ccids[i], i))
             return -1;
     dccp_feat_print_fnlist(fn);
     return 0;
 }
 
 /**
  * dccp_feat_server_ccid_dependencies  -  Resolve CCID-dependent features
  * @dreq: server socket to resolve
  *
  * It is the server which resolves the dependencies once the CCID has been
  * fully negotiated. If no CCID has been negotiated, it uses the default CCID.
  */
 int dccp_feat_server_ccid_dependencies(struct dccp_request_sock *dreq)
 {
     struct list_head *fn = &dreq->dreq_featneg;
     struct dccp_feat_entry *entry;
     u8 is_local, ccid;
 
     for (is_local = 0; is_local <= 1; is_local++) {
         entry = dccp_feat_list_lookup(fn, DCCPF_CCID, is_local);
 
         if (entry != NULL && !entry->empty_confirm)
             ccid = entry->val.sp.vec[0];
         else
             ccid = dccp_feat_default_value(DCCPF_CCID);
 
         if (dccp_feat_propagate_ccid(fn, ccid, is_local))
             return -1;
     }
     return 0;
 }
 
 /* Select the first entry in @servlist that also occurs in @clilist (6.3.1) */
 static int dccp_feat_preflist_match(u8 *servlist, u8 slen, u8 *clilist, u8 clen)
 {
     u8 c, s;
 
     for (s = 0; s < slen; s++)
         for (c = 0; c < clen; c++)
             if (servlist[s] == clilist[c])
                 return servlist[s];
     return -1;
 }
 
 /**
  * dccp_feat_prefer  -  Move preferred entry to the start of array
  * @preferred_value: entry to move to start of array
  * @array: array of preferred entries
  * @array_len: size of the array
  *
  * Reorder the @array_len elements in @array so that @preferred_value comes
  * first. Returns >0 to indicate that @preferred_value does occur in @array.
  */
 static u8 dccp_feat_prefer(u8 preferred_value, u8 *array, u8 array_len)
 {
     u8 i, does_occur = 0;
 
     if (array != NULL) {
         for (i = 0; i < array_len; i++)
             if (array[i] == preferred_value) {
                 array[i] = array[0];
                 does_occur++;
             }
         if (does_occur)
             array[0] = preferred_value;
     }
     return does_occur;
 }
 
 /**
  * dccp_feat_reconcile  -  Reconcile SP preference lists
  *  @fv: SP list to reconcile into
  *  @arr: received SP preference list
  *  @len: length of @arr in bytes
  *  @is_server: whether this side is the server (and @fv is the server's list)
  *  @reorder: whether to reorder the list in @fv after reconciling with @arr
  * When successful, > 0 is returned and the reconciled list is in @fval.
  * A value of 0 means that negotiation failed (no shared entry).
  */
 static int dccp_feat_reconcile(dccp_feat_val *fv, u8 *arr, u8 len,
                    bool is_server, bool reorder)
 {
     int rc;
 
     if (!fv->sp.vec || !arr) {
         DCCP_CRIT("NULL feature value or array");
         return 0;
     }
 
     if (is_server)
         rc = dccp_feat_preflist_match(fv->sp.vec, fv->sp.len, arr, len);
     else
         rc = dccp_feat_preflist_match(arr, len, fv->sp.vec, fv->sp.len);
 
     if (!reorder)
         return rc;
     if (rc < 0)
         return 0;
 
     /*
      * Reorder list: used for activating features and in dccp_insert_fn_opt.
      */
     return dccp_feat_prefer(rc, fv->sp.vec, fv->sp.len);
 }
 
 /**
  * dccp_feat_change_recv  -  Process incoming ChangeL/R options
  * @fn: feature-negotiation list to update
  * @is_mandatory: whether the Change was preceded by a Mandatory option
  * @opt: %DCCPO_CHANGE_L or %DCCPO_CHANGE_R
  * @feat: one of %dccp_feature_numbers
  * @val: NN value or SP value/preference list
  * @len: length of @val in bytes
  * @server: whether this node is the server (1) or the client (0)
  */
 static u8 dccp_feat_change_recv(struct list_head *fn, u8 is_mandatory, u8 opt,
                 u8 feat, u8 *val, u8 len, const bool server)
 {
     u8 defval, type = dccp_feat_type(feat);
     const bool local = (opt == DCCPO_CHANGE_R);
     struct dccp_feat_entry *entry;
     dccp_feat_val fval;
 
     if (len == 0 || type == FEAT_UNKNOWN)       /* 6.1 and 6.6.8 */
         goto unknown_feature_or_value;
 
     dccp_feat_print_opt(opt, feat, val, len, is_mandatory);
 
     /*
      *  Negotiation of NN features: Change R is invalid, so there is no
      *  simultaneous negotiation; hence we do not look up in the list.
      */
     if (type == FEAT_NN) {
         if (local || len > sizeof(fval.nn))
             goto unknown_feature_or_value;
 
         /* 6.3.2: "The feature remote MUST accept any valid value..." */
         fval.nn = dccp_decode_value_var(val, len);
         if (!dccp_feat_is_valid_nn_val(feat, fval.nn))
             goto unknown_feature_or_value;
 
         return dccp_feat_push_confirm(fn, feat, local, &fval);
     }
 
     /*
      *  Unidirectional/simultaneous negotiation of SP features (6.3.1)
      */
     entry = dccp_feat_list_lookup(fn, feat, local);
     if (entry == NULL) {
         /*
          * No particular preferences have been registered. We deal with
          * this situation by assuming that all valid values are equally
          * acceptable, and apply the following checks:
          * - if the peer's list is a singleton, we accept a valid value;
          * - if we are the server, we first try to see if the peer (the
          *   client) advertises the default value. If yes, we use it,
          *   otherwise we accept the preferred value;
          * - else if we are the client, we use the first list element.
          */
         if (dccp_feat_clone_sp_val(&fval, val, 1))
             return DCCP_RESET_CODE_TOO_BUSY;
 
         if (len > 1 && server) {
             defval = dccp_feat_default_value(feat);
             if (dccp_feat_preflist_match(&defval, 1, val, len) > -1)
                 fval.sp.vec[0] = defval;
         } else if (!dccp_feat_is_valid_sp_val(feat, fval.sp.vec[0])) {
             kfree(fval.sp.vec);
             goto unknown_feature_or_value;
         }
 
         /* Treat unsupported CCIDs like invalid values */
         if (feat == DCCPF_CCID && !ccid_support_check(fval.sp.vec, 1)) {
             kfree(fval.sp.vec);
             goto not_valid_or_not_known;
         }
 
         return dccp_feat_push_confirm(fn, feat, local, &fval);
 
     } else if (entry->state == FEAT_UNSTABLE) { /* 6.6.2 */
         return 0;
     }
 
     if (dccp_feat_reconcile(&entry->val, val, len, server, true)) {
         entry->empty_confirm = false;
     } else if (is_mandatory) {
         return DCCP_RESET_CODE_MANDATORY_ERROR;
     } else if (entry->state == FEAT_INITIALISING) {
         /*
          * Failed simultaneous negotiation (server only): try to `save'
          * the connection by checking whether entry contains the default
          * value for @feat. If yes, send an empty Confirm to signal that
          * the received Change was not understood - which implies using
          * the default value.
          * If this also fails, we use Reset as the last resort.
          */
         WARN_ON(!server);
         defval = dccp_feat_default_value(feat);
         if (!dccp_feat_reconcile(&entry->val, &defval, 1, server, true))
             return DCCP_RESET_CODE_OPTION_ERROR;
         entry->empty_confirm = true;
     }
     entry->needs_confirm   = true;
     entry->needs_mandatory = false;
     entry->state           = FEAT_STABLE;
     return 0;
 
 unknown_feature_or_value:
     if (!is_mandatory)
         return dccp_push_empty_confirm(fn, feat, local);
 
 not_valid_or_not_known:
     return is_mandatory ? DCCP_RESET_CODE_MANDATORY_ERROR
                 : DCCP_RESET_CODE_OPTION_ERROR;
 }
 
 /**
  * dccp_feat_confirm_recv  -  Process received Confirm options
  * @fn: feature-negotiation list to update
  * @is_mandatory: whether @opt was preceded by a Mandatory option
  * @opt: %DCCPO_CONFIRM_L or %DCCPO_CONFIRM_R
  * @feat: one of %dccp_feature_numbers
  * @val: NN value or SP value/preference list
  * @len: length of @val in bytes
  * @server: whether this node is server (1) or client (0)
  */
 static u8 dccp_feat_confirm_recv(struct list_head *fn, u8 is_mandatory, u8 opt,
                  u8 feat, u8 *val, u8 len, const bool server)
 {
     u8 *plist, plen, type = dccp_feat_type(feat);
     const bool local = (opt == DCCPO_CONFIRM_R);
     struct dccp_feat_entry *entry = dccp_feat_list_lookup(fn, feat, local);
 
     dccp_feat_print_opt(opt, feat, val, len, is_mandatory);
 
     if (entry == NULL) {    /* nothing queued: ignore or handle error */
         if (is_mandatory && type == FEAT_UNKNOWN)
             return DCCP_RESET_CODE_MANDATORY_ERROR;
 
         if (!local && type == FEAT_NN)      /* 6.3.2 */
             goto confirmation_failed;
         return 0;
     }
 
     if (entry->state != FEAT_CHANGING)      /* 6.6.2 */
         return 0;
 
     if (len == 0) {
         if (dccp_feat_must_be_understood(feat)) /* 6.6.7 */
             goto confirmation_failed;
         /*
          * Empty Confirm during connection setup: this means reverting
          * to the `old' value, which in this case is the default. Since
          * we handle default values automatically when no other values
          * have been set, we revert to the old value by removing this
          * entry from the list.
          */
         dccp_feat_list_pop(entry);
         return 0;
     }
 
     if (type == FEAT_NN) {
         if (len > sizeof(entry->val.nn))
             goto confirmation_failed;
 
         if (entry->val.nn == dccp_decode_value_var(val, len))
             goto confirmation_succeeded;
 
         DCCP_WARN("Bogus Confirm for non-existing value\n");
         goto confirmation_failed;
     }
 
     /*
      * Parsing SP Confirms: the first element of @val is the preferred
      * SP value which the peer confirms, the remainder depends on @len.
      * Note that only the confirmed value need to be a valid SP value.
      */
     if (!dccp_feat_is_valid_sp_val(feat, *val))
         goto confirmation_failed;
 
     if (len == 1) {     /* peer didn't supply a preference list */
         plist = val;
         plen  = len;
     } else {        /* preferred value + preference list */
         plist = val + 1;
         plen  = len - 1;
     }
 
     /* Check whether the peer got the reconciliation right (6.6.8) */
     if (dccp_feat_reconcile(&entry->val, plist, plen, server, 0) != *val) {
         DCCP_WARN("Confirm selected the wrong value %u\n", *val);
         return DCCP_RESET_CODE_OPTION_ERROR;
     }
     entry->val.sp.vec[0] = *val;
 
 confirmation_succeeded:
     entry->state = FEAT_STABLE;
     return 0;
 
 confirmation_failed:
     DCCP_WARN("Confirmation failed\n");
     return is_mandatory ? DCCP_RESET_CODE_MANDATORY_ERROR
                 : DCCP_RESET_CODE_OPTION_ERROR;
 }
 
 /**
  * dccp_feat_handle_nn_established  -  Fast-path reception of NN options
  * @sk:     socket of an established DCCP connection
  * @mandatory:  whether @opt was preceded by a Mandatory option
  * @opt:    %DCCPO_CHANGE_L | %DCCPO_CONFIRM_R (NN only)
  * @feat:   NN number, one of %dccp_feature_numbers
  * @val:    NN value
  * @len:    length of @val in bytes
  *
  * This function combines the functionality of change_recv/confirm_recv, with
  * the following differences (reset codes are the same):
  *    - cleanup after receiving the Confirm;
  *    - values are directly activated after successful parsing;
  *    - deliberately restricted to NN features.
  * The restriction to NN features is essential since SP features can have non-
  * predictable outcomes (depending on the remote configuration), and are inter-
  * dependent (CCIDs for instance cause further dependencies).
  */
 static u8 dccp_feat_handle_nn_established(struct sock *sk, u8 mandatory, u8 opt,
                       u8 feat, u8 *val, u8 len)
 {
     struct list_head *fn = &dccp_sk(sk)->dccps_featneg;
     const bool local = (opt == DCCPO_CONFIRM_R);
     struct dccp_feat_entry *entry;
     u8 type = dccp_feat_type(feat);
     dccp_feat_val fval;
 
     dccp_feat_print_opt(opt, feat, val, len, mandatory);
 
     /* Ignore non-mandatory unknown and non-NN features */
     if (type == FEAT_UNKNOWN) {
         if (local && !mandatory)
             return 0;
         goto fast_path_unknown;
     } else if (type != FEAT_NN) {
         return 0;
     }
 
     /*
      * We don't accept empty Confirms, since in fast-path feature
      * negotiation the values are enabled immediately after sending
      * the Change option.
      * Empty Changes on the other hand are invalid (RFC 4340, 6.1).
      */
     if (len == 0 || len > sizeof(fval.nn))
         goto fast_path_unknown;
 
     if (opt == DCCPO_CHANGE_L) {
         fval.nn = dccp_decode_value_var(val, len);
         if (!dccp_feat_is_valid_nn_val(feat, fval.nn))
             goto fast_path_unknown;
 
         if (dccp_feat_push_confirm(fn, feat, local, &fval) ||
             dccp_feat_activate(sk, feat, local, &fval))
             return DCCP_RESET_CODE_TOO_BUSY;
 
         /* set the `Ack Pending' flag to piggyback a Confirm */
         inet_csk_schedule_ack(sk);
 
     } else if (opt == DCCPO_CONFIRM_R) {
         entry = dccp_feat_list_lookup(fn, feat, local);
         if (entry == NULL || entry->state != FEAT_CHANGING)
             return 0;
 
         fval.nn = dccp_decode_value_var(val, len);
         /*
          * Just ignore a value that doesn't match our current value.
          * If the option changes twice within two RTTs, then at least
          * one CONFIRM will be received for the old value after a
          * new CHANGE was sent.
          */
         if (fval.nn != entry->val.nn)
             return 0;
 
         /* Only activate after receiving the Confirm option (6.6.1). */
         dccp_feat_activate(sk, feat, local, &fval);
 
         /* It has been confirmed - so remove the entry */
         dccp_feat_list_pop(entry);
 
     } else {
         DCCP_WARN("Received illegal option %u\n", opt);
         goto fast_path_failed;
     }
     return 0;
 
 fast_path_unknown:
     if (!mandatory)
         return dccp_push_empty_confirm(fn, feat, local);
 
 fast_path_failed:
     return mandatory ? DCCP_RESET_CODE_MANDATORY_ERROR
              : DCCP_RESET_CODE_OPTION_ERROR;
 }
 
 /**
  * dccp_feat_parse_options  -  Process Feature-Negotiation Options
  * @sk: for general use and used by the client during connection setup
  * @dreq: used by the server during connection setup
  * @mandatory: whether @opt was preceded by a Mandatory option
  * @opt: %DCCPO_CHANGE_L | %DCCPO_CHANGE_R | %DCCPO_CONFIRM_L | %DCCPO_CONFIRM_R
  * @feat: one of %dccp_feature_numbers
  * @val: value contents of @opt
  * @len: length of @val in bytes
  *
  * Returns 0 on success, a Reset code for ending the connection otherwise.
  */
 int dccp_feat_parse_options(struct sock *sk, struct dccp_request_sock *dreq,
                 u8 mandatory, u8 opt, u8 feat, u8 *val, u8 len)
 {
     struct dccp_sock *dp = dccp_sk(sk);
     struct list_head *fn = dreq ? &dreq->dreq_featneg : &dp->dccps_featneg;
     bool server = false;
 
     switch (sk->sk_state) {
     /*
      *  Negotiation during connection setup
      */
     case DCCP_LISTEN:
         server = true;
         fallthrough;
     case DCCP_REQUESTING:
         switch (opt) {
         case DCCPO_CHANGE_L:
         case DCCPO_CHANGE_R:
             return dccp_feat_change_recv(fn, mandatory, opt, feat,
                              val, len, server);
         case DCCPO_CONFIRM_R:
         case DCCPO_CONFIRM_L:
             return dccp_feat_confirm_recv(fn, mandatory, opt, feat,
                               val, len, server);
         }
         break;
     /*
      *  Support for exchanging NN options on an established connection.
      */
     case DCCP_OPEN:
     case DCCP_PARTOPEN:
         return dccp_feat_handle_nn_established(sk, mandatory, opt, feat,
                                val, len);
     }
     return 0;   /* ignore FN options in all other states */
 }
 
 /**
  * dccp_feat_init  -  Seed feature negotiation with host-specific defaults
  * @sk: Socket to initialize.
  *
  * This initialises global defaults, depending on the value of the sysctls.
  * These can later be overridden by registering changes via setsockopt calls.
  * The last link in the chain is finalise_settings, to make sure that between
  * here and the start of actual feature negotiation no inconsistencies enter.
  *
  * All features not appearing below use either defaults or are otherwise
  * later adjusted through dccp_feat_finalise_settings().
  */
 int dccp_feat_init(struct sock *sk)
 {
     struct list_head *fn = &dccp_sk(sk)->dccps_featneg;
     u8 on = 1, off = 0;
     int rc;
     struct {
         u8 *val;
         u8 len;
     } tx, rx;
 
     /* Non-negotiable (NN) features */
     rc = __feat_register_nn(fn, DCCPF_SEQUENCE_WINDOW, 0,
                     sysctl_dccp_sequence_window);
     if (rc)
         return rc;
 
     /* Server-priority (SP) features */
 
     /* Advertise that short seqnos are not supported (7.6.1) */
     rc = __feat_register_sp(fn, DCCPF_SHORT_SEQNOS, true, true, &off, 1);
     if (rc)
         return rc;
 
     /* RFC 4340 12.1: "If a DCCP is not ECN capable, ..." */
     rc = __feat_register_sp(fn, DCCPF_ECN_INCAPABLE, true, true, &on, 1);
     if (rc)
         return rc;
 
     /*
      * We advertise the available list of CCIDs and reorder according to
      * preferences, to avoid failure resulting from negotiating different
      * singleton values (which always leads to failure).
      * These settings can still (later) be overridden via sockopts.
      */
     if (ccid_get_builtin_ccids(&tx.val, &tx.len))
         return -ENOBUFS;
     if (ccid_get_builtin_ccids(&rx.val, &rx.len)) {
         kfree(tx.val);
         return -ENOBUFS;
     }
 
     if (!dccp_feat_prefer(sysctl_dccp_tx_ccid, tx.val, tx.len) ||
         !dccp_feat_prefer(sysctl_dccp_rx_ccid, rx.val, rx.len))
         goto free_ccid_lists;
 
     rc = __feat_register_sp(fn, DCCPF_CCID, true, false, tx.val, tx.len);
     if (rc)
         goto free_ccid_lists;
 
     rc = __feat_register_sp(fn, DCCPF_CCID, false, false, rx.val, rx.len);
 
 free_ccid_lists:
     kfree(tx.val);
     kfree(rx.val);
     return rc;
 }
 
 int dccp_feat_activate_values(struct sock *sk, struct list_head *fn_list)
 {
     struct dccp_sock *dp = dccp_sk(sk);
     struct dccp_feat_entry *cur, *next;
     int idx;
     dccp_feat_val *fvals[DCCP_FEAT_SUPPORTED_MAX][2] = {
          [0 ... DCCP_FEAT_SUPPORTED_MAX-1] = { NULL, NULL }
     };
 
     list_for_each_entry(cur, fn_list, node) {
         /*
          * An empty Confirm means that either an unknown feature type
          * or an invalid value was present. In the first case there is
          * nothing to activate, in the other the default value is used.
          */
         if (cur->empty_confirm)
             continue;
 
         idx = dccp_feat_index(cur->feat_num);
         if (idx < 0) {
             DCCP_BUG("Unknown feature %u", cur->feat_num);
             goto activation_failed;
         }
         if (cur->state != FEAT_STABLE) {
             DCCP_CRIT("Negotiation of %s %s failed in state %s",
                   cur->is_local ? "local" : "remote",
                   dccp_feat_fname(cur->feat_num),
                   dccp_feat_sname[cur->state]);
             goto activation_failed;
         }
         fvals[idx][cur->is_local] = &cur->val;
     }
 
     /*
      * Activate in decreasing order of index, so that the CCIDs are always
      * activated as the last feature. This avoids the case where a CCID
      * relies on the initialisation of one or more features that it depends
      * on (e.g. Send NDP Count, Send Ack Vector, and Ack Ratio features).
      */
     for (idx = DCCP_FEAT_SUPPORTED_MAX; --idx >= 0;)
         if (__dccp_feat_activate(sk, idx, 0, fvals[idx][0]) ||
             __dccp_feat_activate(sk, idx, 1, fvals[idx][1])) {
             DCCP_CRIT("Could not activate %d", idx);
             goto activation_failed;
         }
 
     /* Clean up Change options which have been confirmed already */
     list_for_each_entry_safe(cur, next, fn_list, node)
         if (!cur->needs_confirm)
             dccp_feat_list_pop(cur);
 
     dccp_pr_debug("Activation OK\n");
     return 0;
 
 activation_failed:
     /*
      * We clean up everything that may have been allocated, since
      * it is difficult to track at which stage negotiation failed.
      * This is ok, since all allocation functions below are robust
      * against NULL arguments.
      */
     ccid_hc_rx_delete(dp->dccps_hc_rx_ccid, sk);
     ccid_hc_tx_delete(dp->dccps_hc_tx_ccid, sk);
     dp->dccps_hc_rx_ccid = dp->dccps_hc_tx_ccid = NULL;
     dccp_ackvec_free(dp->dccps_hc_rx_ackvec);
     dp->dccps_hc_rx_ackvec = NULL;
     return -1;
 }

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