security/selinux/xfrm.c

0001 // SPDX-License-Identifier: GPL-2.0-only
0002 /*
0003  *  NSA Security-Enhanced Linux (SELinux) security module
0004  *
0005  *  This file contains the SELinux XFRM hook function implementations.
0006  *
0007  *  Authors:  Serge Hallyn <sergeh@us.ibm.com>
0008  *        Trent Jaeger <jaegert@us.ibm.com>
0009  *
0010  *  Updated: Venkat Yekkirala <vyekkirala@TrustedCS.com>
0011  *
0012  *           Granular IPSec Associations for use in MLS environments.
0013  *
0014  *  Copyright (C) 2005 International Business Machines Corporation
0015  *  Copyright (C) 2006 Trusted Computer Solutions, Inc.
0016  */
0017
0018 /*
0019  * USAGE:
0020  * NOTES:
0021  *   1. Make sure to enable the following options in your kernel config:
0022  *  CONFIG_SECURITY=y
0023  *  CONFIG_SECURITY_NETWORK=y
0024  *  CONFIG_SECURITY_NETWORK_XFRM=y
0025  *  CONFIG_SECURITY_SELINUX=m/y
0026  * ISSUES:
0027  *   1. Caching packets, so they are not dropped during negotiation
0028  *   2. Emulating a reasonable SO_PEERSEC across machines
0029  *   3. Testing addition of sk_policy's with security context via setsockopt
0030  */
0031 #include <linux/kernel.h>
0032 #include <linux/init.h>
0033 #include <linux/security.h>
0034 #include <linux/types.h>
0035 #include <linux/slab.h>
0036 #include <linux/ip.h>
0037 #include <linux/tcp.h>
0038 #include <linux/skbuff.h>
0039 #include <linux/xfrm.h>
0040 #include <net/xfrm.h>
0041 #include <net/checksum.h>
0042 #include <net/udp.h>
0043 #include <linux/atomic.h>
0044
0045 #include "avc.h"
0046 #include "objsec.h"
0047 #include "xfrm.h"
0048
0049 /* Labeled XFRM instance counter */
0050 atomic_t selinux_xfrm_refcount __read_mostly = ATOMIC_INIT(0);
0051
0052 /*
0053  * Returns true if the context is an LSM/SELinux context.
0054  */
0055 static inline int selinux_authorizable_ctx(struct xfrm_sec_ctx *ctx)
0056 {
0057     return (ctx &&
0058         (ctx->ctx_doi == XFRM_SC_DOI_LSM) &&
0059         (ctx->ctx_alg == XFRM_SC_ALG_SELINUX));
0060 }
0061
0062 /*
0063  * Returns true if the xfrm contains a security blob for SELinux.
0064  */
0065 static inline int selinux_authorizable_xfrm(struct xfrm_state *x)
0066 {
0067     return selinux_authorizable_ctx(x->security);
0068 }
0069
0070 /*
0071  * Allocates a xfrm_sec_state and populates it using the supplied security
0072  * xfrm_user_sec_ctx context.
0073  */
0074 static int selinux_xfrm_alloc_user(struct xfrm_sec_ctx **ctxp,
0075                    struct xfrm_user_sec_ctx *uctx,
0076                    gfp_t gfp)
0077 {
0078     int rc;
0079     const struct task_security_struct *tsec = selinux_cred(current_cred());
0080     struct xfrm_sec_ctx *ctx = NULL;
0081     u32 str_len;
0082
0083     if (ctxp == NULL || uctx == NULL ||
0084         uctx->ctx_doi != XFRM_SC_DOI_LSM ||
0085         uctx->ctx_alg != XFRM_SC_ALG_SELINUX)
0086         return -EINVAL;
0087
0088     str_len = uctx->ctx_len;
0089     if (str_len >= PAGE_SIZE)
0090         return -ENOMEM;
0091
0092     ctx = kmalloc(struct_size(ctx, ctx_str, str_len + 1), gfp);
0093     if (!ctx)
0094         return -ENOMEM;
0095
0096     ctx->ctx_doi = XFRM_SC_DOI_LSM;
0097     ctx->ctx_alg = XFRM_SC_ALG_SELINUX;
0098     ctx->ctx_len = str_len;
0099     memcpy(ctx->ctx_str, &uctx[1], str_len);
0100     ctx->ctx_str[str_len] = '\0';
0101     rc = security_context_to_sid(&selinux_state, ctx->ctx_str, str_len,
0102                      &ctx->ctx_sid, gfp);
0103     if (rc)
0104         goto err;
0105
0106     rc = avc_has_perm(&selinux_state,
0107               tsec->sid, ctx->ctx_sid,
0108               SECCLASS_ASSOCIATION, ASSOCIATION__SETCONTEXT, NULL);
0109     if (rc)
0110         goto err;
0111
0112     *ctxp = ctx;
0113     atomic_inc(&selinux_xfrm_refcount);
0114     return 0;
0115
0116 err:
0117     kfree(ctx);
0118     return rc;
0119 }
0120
0121 /*
0122  * Free the xfrm_sec_ctx structure.
0123  */
0124 static void selinux_xfrm_free(struct xfrm_sec_ctx *ctx)
0125 {
0126     if (!ctx)
0127         return;
0128
0129     atomic_dec(&selinux_xfrm_refcount);
0130     kfree(ctx);
0131 }
0132
0133 /*
0134  * Authorize the deletion of a labeled SA or policy rule.
0135  */
0136 static int selinux_xfrm_delete(struct xfrm_sec_ctx *ctx)
0137 {
0138     const struct task_security_struct *tsec = selinux_cred(current_cred());
0139
0140     if (!ctx)
0141         return 0;
0142
0143     return avc_has_perm(&selinux_state,
0144                 tsec->sid, ctx->ctx_sid,
0145                 SECCLASS_ASSOCIATION, ASSOCIATION__SETCONTEXT,
0146                 NULL);
0147 }
0148
0149 /*
0150  * LSM hook implementation that authorizes that a flow can use a xfrm policy
0151  * rule.
0152  */
0153 int selinux_xfrm_policy_lookup(struct xfrm_sec_ctx *ctx, u32 fl_secid)
0154 {
0155     int rc;
0156
0157     /* All flows should be treated as polmatch'ing an otherwise applicable
0158      * "non-labeled" policy. This would prevent inadvertent "leaks". */
0159     if (!ctx)
0160         return 0;
0161
0162     /* Context sid is either set to label or ANY_ASSOC */
0163     if (!selinux_authorizable_ctx(ctx))
0164         return -EINVAL;
0165
0166     rc = avc_has_perm(&selinux_state,
0167               fl_secid, ctx->ctx_sid,
0168               SECCLASS_ASSOCIATION, ASSOCIATION__POLMATCH, NULL);
0169     return (rc == -EACCES ? -ESRCH : rc);
0170 }
0171
0172 /*
0173  * LSM hook implementation that authorizes that a state matches
0174  * the given policy, flow combo.
0175  */
0176 int selinux_xfrm_state_pol_flow_match(struct xfrm_state *x,
0177                       struct xfrm_policy *xp,
0178                       const struct flowi_common *flic)
0179 {
0180     u32 state_sid;
0181     u32 flic_sid;
0182
0183     if (!xp->security)
0184         if (x->security)
0185             /* unlabeled policy and labeled SA can't match */
0186             return 0;
0187         else
0188             /* unlabeled policy and unlabeled SA match all flows */
0189             return 1;
0190     else
0191         if (!x->security)
0192             /* unlabeled SA and labeled policy can't match */
0193             return 0;
0194         else
0195             if (!selinux_authorizable_xfrm(x))
0196                 /* Not a SELinux-labeled SA */
0197                 return 0;
0198
0199     state_sid = x->security->ctx_sid;
0200     flic_sid = flic->flowic_secid;
0201
0202     if (flic_sid != state_sid)
0203         return 0;
0204
0205     /* We don't need a separate SA Vs. policy polmatch check since the SA
0206      * is now of the same label as the flow and a flow Vs. policy polmatch
0207      * check had already happened in selinux_xfrm_policy_lookup() above. */
0208     return (avc_has_perm(&selinux_state, flic_sid, state_sid,
0209                  SECCLASS_ASSOCIATION, ASSOCIATION__SENDTO,
0210                  NULL) ? 0 : 1);
0211 }
0212
0213 static u32 selinux_xfrm_skb_sid_egress(struct sk_buff *skb)
0214 {
0215     struct dst_entry *dst = skb_dst(skb);
0216     struct xfrm_state *x;
0217
0218     if (dst == NULL)
0219         return SECSID_NULL;
0220     x = dst->xfrm;
0221     if (x == NULL || !selinux_authorizable_xfrm(x))
0222         return SECSID_NULL;
0223
0224     return x->security->ctx_sid;
0225 }
0226
0227 static int selinux_xfrm_skb_sid_ingress(struct sk_buff *skb,
0228                     u32 *sid, int ckall)
0229 {
0230     u32 sid_session = SECSID_NULL;
0231     struct sec_path *sp = skb_sec_path(skb);
0232
0233     if (sp) {
0234         int i;
0235
0236         for (i = sp->len - 1; i >= 0; i--) {
0237             struct xfrm_state *x = sp->xvec[i];
0238             if (selinux_authorizable_xfrm(x)) {
0239                 struct xfrm_sec_ctx *ctx = x->security;
0240
0241                 if (sid_session == SECSID_NULL) {
0242                     sid_session = ctx->ctx_sid;
0243                     if (!ckall)
0244                         goto out;
0245                 } else if (sid_session != ctx->ctx_sid) {
0246                     *sid = SECSID_NULL;
0247                     return -EINVAL;
0248                 }
0249             }
0250         }
0251     }
0252
0253 out:
0254     *sid = sid_session;
0255     return 0;
0256 }
0257
0258 /*
0259  * LSM hook implementation that checks and/or returns the xfrm sid for the
0260  * incoming packet.
0261  */
0262 int selinux_xfrm_decode_session(struct sk_buff *skb, u32 *sid, int ckall)
0263 {
0264     if (skb == NULL) {
0265         *sid = SECSID_NULL;
0266         return 0;
0267     }
0268     return selinux_xfrm_skb_sid_ingress(skb, sid, ckall);
0269 }
0270
0271 int selinux_xfrm_skb_sid(struct sk_buff *skb, u32 *sid)
0272 {
0273     int rc;
0274
0275     rc = selinux_xfrm_skb_sid_ingress(skb, sid, 0);
0276     if (rc == 0 && *sid == SECSID_NULL)
0277         *sid = selinux_xfrm_skb_sid_egress(skb);
0278
0279     return rc;
0280 }
0281
0282 /*
0283  * LSM hook implementation that allocs and transfers uctx spec to xfrm_policy.
0284  */
0285 int selinux_xfrm_policy_alloc(struct xfrm_sec_ctx **ctxp,
0286                   struct xfrm_user_sec_ctx *uctx,
0287                   gfp_t gfp)
0288 {
0289     return selinux_xfrm_alloc_user(ctxp, uctx, gfp);
0290 }
0291
0292 /*
0293  * LSM hook implementation that copies security data structure from old to new
0294  * for policy cloning.
0295  */
0296 int selinux_xfrm_policy_clone(struct xfrm_sec_ctx *old_ctx,
0297                   struct xfrm_sec_ctx **new_ctxp)
0298 {
0299     struct xfrm_sec_ctx *new_ctx;
0300
0301     if (!old_ctx)
0302         return 0;
0303
0304     new_ctx = kmemdup(old_ctx, sizeof(*old_ctx) + old_ctx->ctx_len,
0305               GFP_ATOMIC);
0306     if (!new_ctx)
0307         return -ENOMEM;
0308     atomic_inc(&selinux_xfrm_refcount);
0309     *new_ctxp = new_ctx;
0310
0311     return 0;
0312 }
0313
0314 /*
0315  * LSM hook implementation that frees xfrm_sec_ctx security information.
0316  */
0317 void selinux_xfrm_policy_free(struct xfrm_sec_ctx *ctx)
0318 {
0319     selinux_xfrm_free(ctx);
0320 }
0321
0322 /*
0323  * LSM hook implementation that authorizes deletion of labeled policies.
0324  */
0325 int selinux_xfrm_policy_delete(struct xfrm_sec_ctx *ctx)
0326 {
0327     return selinux_xfrm_delete(ctx);
0328 }
0329
0330 /*
0331  * LSM hook implementation that allocates a xfrm_sec_state, populates it using
0332  * the supplied security context, and assigns it to the xfrm_state.
0333  */
0334 int selinux_xfrm_state_alloc(struct xfrm_state *x,
0335                  struct xfrm_user_sec_ctx *uctx)
0336 {
0337     return selinux_xfrm_alloc_user(&x->security, uctx, GFP_KERNEL);
0338 }
0339
0340 /*
0341  * LSM hook implementation that allocates a xfrm_sec_state and populates based
0342  * on a secid.
0343  */
0344 int selinux_xfrm_state_alloc_acquire(struct xfrm_state *x,
0345                      struct xfrm_sec_ctx *polsec, u32 secid)
0346 {
0347     int rc;
0348     struct xfrm_sec_ctx *ctx;
0349     char *ctx_str = NULL;
0350     u32 str_len;
0351
0352     if (!polsec)
0353         return 0;
0354
0355     if (secid == 0)
0356         return -EINVAL;
0357
0358     rc = security_sid_to_context(&selinux_state, secid, &ctx_str,
0359                      &str_len);
0360     if (rc)
0361         return rc;
0362
0363     ctx = kmalloc(struct_size(ctx, ctx_str, str_len), GFP_ATOMIC);
0364     if (!ctx) {
0365         rc = -ENOMEM;
0366         goto out;
0367     }
0368
0369     ctx->ctx_doi = XFRM_SC_DOI_LSM;
0370     ctx->ctx_alg = XFRM_SC_ALG_SELINUX;
0371     ctx->ctx_sid = secid;
0372     ctx->ctx_len = str_len;
0373     memcpy(ctx->ctx_str, ctx_str, str_len);
0374
0375     x->security = ctx;
0376     atomic_inc(&selinux_xfrm_refcount);
0377 out:
0378     kfree(ctx_str);
0379     return rc;
0380 }
0381
0382 /*
0383  * LSM hook implementation that frees xfrm_state security information.
0384  */
0385 void selinux_xfrm_state_free(struct xfrm_state *x)
0386 {
0387     selinux_xfrm_free(x->security);
0388 }
0389
0390 /*
0391  * LSM hook implementation that authorizes deletion of labeled SAs.
0392  */
0393 int selinux_xfrm_state_delete(struct xfrm_state *x)
0394 {
0395     return selinux_xfrm_delete(x->security);
0396 }
0397
0398 /*
0399  * LSM hook that controls access to unlabelled packets.  If
0400  * a xfrm_state is authorizable (defined by macro) then it was
0401  * already authorized by the IPSec process.  If not, then
0402  * we need to check for unlabelled access since this may not have
0403  * gone thru the IPSec process.
0404  */
0405 int selinux_xfrm_sock_rcv_skb(u32 sk_sid, struct sk_buff *skb,
0406                   struct common_audit_data *ad)
0407 {
0408     int i;
0409     struct sec_path *sp = skb_sec_path(skb);
0410     u32 peer_sid = SECINITSID_UNLABELED;
0411
0412     if (sp) {
0413         for (i = 0; i < sp->len; i++) {
0414             struct xfrm_state *x = sp->xvec[i];
0415
0416             if (x && selinux_authorizable_xfrm(x)) {
0417                 struct xfrm_sec_ctx *ctx = x->security;
0418                 peer_sid = ctx->ctx_sid;
0419                 break;
0420             }
0421         }
0422     }
0423
0424     /* This check even when there's no association involved is intended,
0425      * according to Trent Jaeger, to make sure a process can't engage in
0426      * non-IPsec communication unless explicitly allowed by policy. */
0427     return avc_has_perm(&selinux_state,
0428                 sk_sid, peer_sid,
0429                 SECCLASS_ASSOCIATION, ASSOCIATION__RECVFROM, ad);
0430 }
0431
0432 /*
0433  * POSTROUTE_LAST hook's XFRM processing:
0434  * If we have no security association, then we need to determine
0435  * whether the socket is allowed to send to an unlabelled destination.
0436  * If we do have a authorizable security association, then it has already been
0437  * checked in the selinux_xfrm_state_pol_flow_match hook above.
0438  */
0439 int selinux_xfrm_postroute_last(u32 sk_sid, struct sk_buff *skb,
0440                 struct common_audit_data *ad, u8 proto)
0441 {
0442     struct dst_entry *dst;
0443
0444     switch (proto) {
0445     case IPPROTO_AH:
0446     case IPPROTO_ESP:
0447     case IPPROTO_COMP:
0448         /* We should have already seen this packet once before it
0449          * underwent xfrm(s). No need to subject it to the unlabeled
0450          * check. */
0451         return 0;
0452     default:
0453         break;
0454     }
0455
0456     dst = skb_dst(skb);
0457     if (dst) {
0458         struct dst_entry *iter;
0459
0460         for (iter = dst; iter != NULL; iter = xfrm_dst_child(iter)) {
0461             struct xfrm_state *x = iter->xfrm;
0462
0463             if (x && selinux_authorizable_xfrm(x))
0464                 return 0;
0465         }
0466     }
0467
0468     /* This check even when there's no association involved is intended,
0469      * according to Trent Jaeger, to make sure a process can't engage in
0470      * non-IPsec communication unless explicitly allowed by policy. */
0471     return avc_has_perm(&selinux_state, sk_sid, SECINITSID_UNLABELED,
0472                 SECCLASS_ASSOCIATION, ASSOCIATION__SENDTO, ad);
0473 }