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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // SPDX-License-Identifier: GPL-2.0-only
 /*
  * Landlock LSM - Filesystem management and hooks
  *
  * Copyright © 2016-2020 Mickaël Salaün <mic@digikod.net>
  * Copyright © 2018-2020 ANSSI
  * Copyright © 2021-2022 Microsoft Corporation
  */
 
 #include <linux/atomic.h>
 #include <linux/bitops.h>
 #include <linux/bits.h>
 #include <linux/compiler_types.h>
 #include <linux/dcache.h>
 #include <linux/err.h>
 #include <linux/fs.h>
 #include <linux/init.h>
 #include <linux/kernel.h>
 #include <linux/limits.h>
 #include <linux/list.h>
 #include <linux/lsm_hooks.h>
 #include <linux/mount.h>
 #include <linux/namei.h>
 #include <linux/path.h>
 #include <linux/rcupdate.h>
 #include <linux/spinlock.h>
 #include <linux/stat.h>
 #include <linux/types.h>
 #include <linux/wait_bit.h>
 #include <linux/workqueue.h>
 #include <uapi/linux/landlock.h>
 
 #include "common.h"
 #include "cred.h"
 #include "fs.h"
 #include "limits.h"
 #include "object.h"
 #include "ruleset.h"
 #include "setup.h"
 
 /* Underlying object management */
 
 static void release_inode(struct landlock_object *const object)
     __releases(object->lock)
 {
     struct inode *const inode = object->underobj;
     struct super_block *sb;
 
     if (!inode) {
         spin_unlock(&object->lock);
         return;
     }
 
     /*
      * Protects against concurrent use by hook_sb_delete() of the reference
      * to the underlying inode.
      */
     object->underobj = NULL;
     /*
      * Makes sure that if the filesystem is concurrently unmounted,
      * hook_sb_delete() will wait for us to finish iput().
      */
     sb = inode->i_sb;
     atomic_long_inc(&landlock_superblock(sb)->inode_refs);
     spin_unlock(&object->lock);
     /*
      * Because object->underobj was not NULL, hook_sb_delete() and
      * get_inode_object() guarantee that it is safe to reset
      * landlock_inode(inode)->object while it is not NULL.  It is therefore
      * not necessary to lock inode->i_lock.
      */
     rcu_assign_pointer(landlock_inode(inode)->object, NULL);
     /*
      * Now, new rules can safely be tied to @inode with get_inode_object().
      */
 
     iput(inode);
     if (atomic_long_dec_and_test(&landlock_superblock(sb)->inode_refs))
         wake_up_var(&landlock_superblock(sb)->inode_refs);
 }
 
 static const struct landlock_object_underops landlock_fs_underops = {
     .release = release_inode
 };
 
 /* Ruleset management */
 
 static struct landlock_object *get_inode_object(struct inode *const inode)
 {
     struct landlock_object *object, *new_object;
     struct landlock_inode_security *inode_sec = landlock_inode(inode);
 
     rcu_read_lock();
 retry:
     object = rcu_dereference(inode_sec->object);
     if (object) {
         if (likely(refcount_inc_not_zero(&object->usage))) {
             rcu_read_unlock();
             return object;
         }
         /*
          * We are racing with release_inode(), the object is going
          * away.  Wait for release_inode(), then retry.
          */
         spin_lock(&object->lock);
         spin_unlock(&object->lock);
         goto retry;
     }
     rcu_read_unlock();
 
     /*
      * If there is no object tied to @inode, then create a new one (without
      * holding any locks).
      */
     new_object = landlock_create_object(&landlock_fs_underops, inode);
     if (IS_ERR(new_object))
         return new_object;
 
     /*
      * Protects against concurrent calls to get_inode_object() or
      * hook_sb_delete().
      */
     spin_lock(&inode->i_lock);
     if (unlikely(rcu_access_pointer(inode_sec->object))) {
         /* Someone else just created the object, bail out and retry. */
         spin_unlock(&inode->i_lock);
         kfree(new_object);
 
         rcu_read_lock();
         goto retry;
     }
 
     /*
      * @inode will be released by hook_sb_delete() on its superblock
      * shutdown, or by release_inode() when no more ruleset references the
      * related object.
      */
     ihold(inode);
     rcu_assign_pointer(inode_sec->object, new_object);
     spin_unlock(&inode->i_lock);
     return new_object;
 }
 
 /* All access rights that can be tied to files. */
 /* clang-format off */
 #define ACCESS_FILE ( \
     LANDLOCK_ACCESS_FS_EXECUTE | \
     LANDLOCK_ACCESS_FS_WRITE_FILE | \
     LANDLOCK_ACCESS_FS_READ_FILE)
 /* clang-format on */
 
 /*
  * All access rights that are denied by default whether they are handled or not
  * by a ruleset/layer.  This must be ORed with all ruleset->fs_access_masks[]
  * entries when we need to get the absolute handled access masks.
  */
 /* clang-format off */
 #define ACCESS_INITIALLY_DENIED ( \
     LANDLOCK_ACCESS_FS_REFER)
 /* clang-format on */
 
 /*
  * @path: Should have been checked by get_path_from_fd().
  */
 int landlock_append_fs_rule(struct landlock_ruleset *const ruleset,
                 const struct path *const path,
                 access_mask_t access_rights)
 {
     int err;
     struct landlock_object *object;
 
     /* Files only get access rights that make sense. */
     if (!d_is_dir(path->dentry) &&
         (access_rights | ACCESS_FILE) != ACCESS_FILE)
         return -EINVAL;
     if (WARN_ON_ONCE(ruleset->num_layers != 1))
         return -EINVAL;
 
     /* Transforms relative access rights to absolute ones. */
     access_rights |=
         LANDLOCK_MASK_ACCESS_FS &
         ~(ruleset->fs_access_masks[0] | ACCESS_INITIALLY_DENIED);
     object = get_inode_object(d_backing_inode(path->dentry));
     if (IS_ERR(object))
         return PTR_ERR(object);
     mutex_lock(&ruleset->lock);
     err = landlock_insert_rule(ruleset, object, access_rights);
     mutex_unlock(&ruleset->lock);
     /*
      * No need to check for an error because landlock_insert_rule()
      * increments the refcount for the new object if needed.
      */
     landlock_put_object(object);
     return err;
 }
 
 /* Access-control management */
 
 /*
  * The lifetime of the returned rule is tied to @domain.
  *
  * Returns NULL if no rule is found or if @dentry is negative.
  */
 static inline const struct landlock_rule *
 find_rule(const struct landlock_ruleset *const domain,
       const struct dentry *const dentry)
 {
     const struct landlock_rule *rule;
     const struct inode *inode;
 
     /* Ignores nonexistent leafs. */
     if (d_is_negative(dentry))
         return NULL;
 
     inode = d_backing_inode(dentry);
     rcu_read_lock();
     rule = landlock_find_rule(
         domain, rcu_dereference(landlock_inode(inode)->object));
     rcu_read_unlock();
     return rule;
 }
 
 /*
  * @layer_masks is read and may be updated according to the access request and
  * the matching rule.
  *
  * Returns true if the request is allowed (i.e. relevant layer masks for the
  * request are empty).
  */
 static inline bool
 unmask_layers(const struct landlock_rule *const rule,
           const access_mask_t access_request,
           layer_mask_t (*const layer_masks)[LANDLOCK_NUM_ACCESS_FS])
 {
     size_t layer_level;
 
     if (!access_request || !layer_masks)
         return true;
     if (!rule)
         return false;
 
     /*
      * An access is granted if, for each policy layer, at least one rule
      * encountered on the pathwalk grants the requested access,
      * regardless of its position in the layer stack.  We must then check
      * the remaining layers for each inode, from the first added layer to
      * the last one.  When there is multiple requested accesses, for each
      * policy layer, the full set of requested accesses may not be granted
      * by only one rule, but by the union (binary OR) of multiple rules.
      * E.g. /a/b <execute> + /a <read> => /a/b <execute + read>
      */
     for (layer_level = 0; layer_level < rule->num_layers; layer_level++) {
         const struct landlock_layer *const layer =
             &rule->layers[layer_level];
         const layer_mask_t layer_bit = BIT_ULL(layer->level - 1);
         const unsigned long access_req = access_request;
         unsigned long access_bit;
         bool is_empty;
 
         /*
          * Records in @layer_masks which layer grants access to each
          * requested access.
          */
         is_empty = true;
         for_each_set_bit(access_bit, &access_req,
                  ARRAY_SIZE(*layer_masks)) {
             if (layer->access & BIT_ULL(access_bit))
                 (*layer_masks)[access_bit] &= ~layer_bit;
             is_empty = is_empty && !(*layer_masks)[access_bit];
         }
         if (is_empty)
             return true;
     }
     return false;
 }
 
 /*
  * Allows access to pseudo filesystems that will never be mountable (e.g.
  * sockfs, pipefs), but can still be reachable through
  * /proc/<pid>/fd/<file-descriptor>
  */
 static inline bool is_nouser_or_private(const struct dentry *dentry)
 {
     return (dentry->d_sb->s_flags & SB_NOUSER) ||
            (d_is_positive(dentry) &&
         unlikely(IS_PRIVATE(d_backing_inode(dentry))));
 }
 
 static inline access_mask_t
 get_handled_accesses(const struct landlock_ruleset *const domain)
 {
     access_mask_t access_dom = ACCESS_INITIALLY_DENIED;
     size_t layer_level;
 
     for (layer_level = 0; layer_level < domain->num_layers; layer_level++)
         access_dom |= domain->fs_access_masks[layer_level];
     return access_dom & LANDLOCK_MASK_ACCESS_FS;
 }
 
 static inline access_mask_t
 init_layer_masks(const struct landlock_ruleset *const domain,
          const access_mask_t access_request,
          layer_mask_t (*const layer_masks)[LANDLOCK_NUM_ACCESS_FS])
 {
     access_mask_t handled_accesses = 0;
     size_t layer_level;
 
     memset(layer_masks, 0, sizeof(*layer_masks));
     /* An empty access request can happen because of O_WRONLY | O_RDWR. */
     if (!access_request)
         return 0;
 
     /* Saves all handled accesses per layer. */
     for (layer_level = 0; layer_level < domain->num_layers; layer_level++) {
         const unsigned long access_req = access_request;
         unsigned long access_bit;
 
         for_each_set_bit(access_bit, &access_req,
                  ARRAY_SIZE(*layer_masks)) {
             /*
              * Artificially handles all initially denied by default
              * access rights.
              */
             if (BIT_ULL(access_bit) &
                 (domain->fs_access_masks[layer_level] |
                  ACCESS_INITIALLY_DENIED)) {
                 (*layer_masks)[access_bit] |=
                     BIT_ULL(layer_level);
                 handled_accesses |= BIT_ULL(access_bit);
             }
         }
     }
     return handled_accesses;
 }
 
 /*
  * Check that a destination file hierarchy has more restrictions than a source
  * file hierarchy.  This is only used for link and rename actions.
  *
  * @layer_masks_child2: Optional child masks.
  */
 static inline bool no_more_access(
     const layer_mask_t (*const layer_masks_parent1)[LANDLOCK_NUM_ACCESS_FS],
     const layer_mask_t (*const layer_masks_child1)[LANDLOCK_NUM_ACCESS_FS],
     const bool child1_is_directory,
     const layer_mask_t (*const layer_masks_parent2)[LANDLOCK_NUM_ACCESS_FS],
     const layer_mask_t (*const layer_masks_child2)[LANDLOCK_NUM_ACCESS_FS],
     const bool child2_is_directory)
 {
     unsigned long access_bit;
 
     for (access_bit = 0; access_bit < ARRAY_SIZE(*layer_masks_parent2);
          access_bit++) {
         /* Ignores accesses that only make sense for directories. */
         const bool is_file_access =
             !!(BIT_ULL(access_bit) & ACCESS_FILE);
 
         if (child1_is_directory || is_file_access) {
             /*
              * Checks if the destination restrictions are a
              * superset of the source ones (i.e. inherited access
              * rights without child exceptions):
              * restrictions(parent2) >= restrictions(child1)
              */
             if ((((*layer_masks_parent1)[access_bit] &
                   (*layer_masks_child1)[access_bit]) |
                  (*layer_masks_parent2)[access_bit]) !=
                 (*layer_masks_parent2)[access_bit])
                 return false;
         }
 
         if (!layer_masks_child2)
             continue;
         if (child2_is_directory || is_file_access) {
             /*
              * Checks inverted restrictions for RENAME_EXCHANGE:
              * restrictions(parent1) >= restrictions(child2)
              */
             if ((((*layer_masks_parent2)[access_bit] &
                   (*layer_masks_child2)[access_bit]) |
                  (*layer_masks_parent1)[access_bit]) !=
                 (*layer_masks_parent1)[access_bit])
                 return false;
         }
     }
     return true;
 }
 
 /*
  * Removes @layer_masks accesses that are not requested.
  *
  * Returns true if the request is allowed, false otherwise.
  */
 static inline bool
 scope_to_request(const access_mask_t access_request,
          layer_mask_t (*const layer_masks)[LANDLOCK_NUM_ACCESS_FS])
 {
     const unsigned long access_req = access_request;
     unsigned long access_bit;
 
     if (WARN_ON_ONCE(!layer_masks))
         return true;
 
     for_each_clear_bit(access_bit, &access_req, ARRAY_SIZE(*layer_masks))
         (*layer_masks)[access_bit] = 0;
     return !memchr_inv(layer_masks, 0, sizeof(*layer_masks));
 }
 
 /*
  * Returns true if there is at least one access right different than
  * LANDLOCK_ACCESS_FS_REFER.
  */
 static inline bool
 is_eacces(const layer_mask_t (*const layer_masks)[LANDLOCK_NUM_ACCESS_FS],
       const access_mask_t access_request)
 {
     unsigned long access_bit;
     /* LANDLOCK_ACCESS_FS_REFER alone must return -EXDEV. */
     const unsigned long access_check = access_request &
                        ~LANDLOCK_ACCESS_FS_REFER;
 
     if (!layer_masks)
         return false;
 
     for_each_set_bit(access_bit, &access_check, ARRAY_SIZE(*layer_masks)) {
         if ((*layer_masks)[access_bit])
             return true;
     }
     return false;
 }
 
 /**
  * check_access_path_dual - Check accesses for requests with a common path
  *
  * @domain: Domain to check against.
  * @path: File hierarchy to walk through.
  * @access_request_parent1: Accesses to check, once @layer_masks_parent1 is
  *     equal to @layer_masks_parent2 (if any).  This is tied to the unique
  *     requested path for most actions, or the source in case of a refer action
  *     (i.e. rename or link), or the source and destination in case of
  *     RENAME_EXCHANGE.
  * @layer_masks_parent1: Pointer to a matrix of layer masks per access
  *     masks, identifying the layers that forbid a specific access.  Bits from
  *     this matrix can be unset according to the @path walk.  An empty matrix
  *     means that @domain allows all possible Landlock accesses (i.e. not only
  *     those identified by @access_request_parent1).  This matrix can
  *     initially refer to domain layer masks and, when the accesses for the
  *     destination and source are the same, to requested layer masks.
  * @dentry_child1: Dentry to the initial child of the parent1 path.  This
  *     pointer must be NULL for non-refer actions (i.e. not link nor rename).
  * @access_request_parent2: Similar to @access_request_parent1 but for a
  *     request involving a source and a destination.  This refers to the
  *     destination, except in case of RENAME_EXCHANGE where it also refers to
  *     the source.  Must be set to 0 when using a simple path request.
  * @layer_masks_parent2: Similar to @layer_masks_parent1 but for a refer
  *     action.  This must be NULL otherwise.
  * @dentry_child2: Dentry to the initial child of the parent2 path.  This
  *     pointer is only set for RENAME_EXCHANGE actions and must be NULL
  *     otherwise.
  *
  * This helper first checks that the destination has a superset of restrictions
  * compared to the source (if any) for a common path.  Because of
  * RENAME_EXCHANGE actions, source and destinations may be swapped.  It then
  * checks that the collected accesses and the remaining ones are enough to
  * allow the request.
  *
  * Returns:
  * - 0 if the access request is granted;
  * - -EACCES if it is denied because of access right other than
  *   LANDLOCK_ACCESS_FS_REFER;
  * - -EXDEV if the renaming or linking would be a privileged escalation
  *   (according to each layered policies), or if LANDLOCK_ACCESS_FS_REFER is
  *   not allowed by the source or the destination.
  */
 static int check_access_path_dual(
     const struct landlock_ruleset *const domain,
     const struct path *const path,
     const access_mask_t access_request_parent1,
     layer_mask_t (*const layer_masks_parent1)[LANDLOCK_NUM_ACCESS_FS],
     const struct dentry *const dentry_child1,
     const access_mask_t access_request_parent2,
     layer_mask_t (*const layer_masks_parent2)[LANDLOCK_NUM_ACCESS_FS],
     const struct dentry *const dentry_child2)
 {
     bool allowed_parent1 = false, allowed_parent2 = false, is_dom_check,
          child1_is_directory = true, child2_is_directory = true;
     struct path walker_path;
     access_mask_t access_masked_parent1, access_masked_parent2;
     layer_mask_t _layer_masks_child1[LANDLOCK_NUM_ACCESS_FS],
         _layer_masks_child2[LANDLOCK_NUM_ACCESS_FS];
     layer_mask_t(*layer_masks_child1)[LANDLOCK_NUM_ACCESS_FS] = NULL,
     (*layer_masks_child2)[LANDLOCK_NUM_ACCESS_FS] = NULL;
 
     if (!access_request_parent1 && !access_request_parent2)
         return 0;
     if (WARN_ON_ONCE(!domain || !path))
         return 0;
     if (is_nouser_or_private(path->dentry))
         return 0;
     if (WARN_ON_ONCE(domain->num_layers < 1 || !layer_masks_parent1))
         return -EACCES;
 
     if (unlikely(layer_masks_parent2)) {
         if (WARN_ON_ONCE(!dentry_child1))
             return -EACCES;
         /*
          * For a double request, first check for potential privilege
          * escalation by looking at domain handled accesses (which are
          * a superset of the meaningful requested accesses).
          */
         access_masked_parent1 = access_masked_parent2 =
             get_handled_accesses(domain);
         is_dom_check = true;
     } else {
         if (WARN_ON_ONCE(dentry_child1 || dentry_child2))
             return -EACCES;
         /* For a simple request, only check for requested accesses. */
         access_masked_parent1 = access_request_parent1;
         access_masked_parent2 = access_request_parent2;
         is_dom_check = false;
     }
 
     if (unlikely(dentry_child1)) {
         unmask_layers(find_rule(domain, dentry_child1),
                   init_layer_masks(domain, LANDLOCK_MASK_ACCESS_FS,
                            &_layer_masks_child1),
                   &_layer_masks_child1);
         layer_masks_child1 = &_layer_masks_child1;
         child1_is_directory = d_is_dir(dentry_child1);
     }
     if (unlikely(dentry_child2)) {
         unmask_layers(find_rule(domain, dentry_child2),
                   init_layer_masks(domain, LANDLOCK_MASK_ACCESS_FS,
                            &_layer_masks_child2),
                   &_layer_masks_child2);
         layer_masks_child2 = &_layer_masks_child2;
         child2_is_directory = d_is_dir(dentry_child2);
     }
 
     walker_path = *path;
     path_get(&walker_path);
     /*
      * We need to walk through all the hierarchy to not miss any relevant
      * restriction.
      */
     while (true) {
         struct dentry *parent_dentry;
         const struct landlock_rule *rule;
 
         /*
          * If at least all accesses allowed on the destination are
          * already allowed on the source, respectively if there is at
          * least as much as restrictions on the destination than on the
          * source, then we can safely refer files from the source to
          * the destination without risking a privilege escalation.
          * This also applies in the case of RENAME_EXCHANGE, which
          * implies checks on both direction.  This is crucial for
          * standalone multilayered security policies.  Furthermore,
          * this helps avoid policy writers to shoot themselves in the
          * foot.
          */
         if (unlikely(is_dom_check &&
                  no_more_access(
                      layer_masks_parent1, layer_masks_child1,
                      child1_is_directory, layer_masks_parent2,
                      layer_masks_child2,
                      child2_is_directory))) {
             allowed_parent1 = scope_to_request(
                 access_request_parent1, layer_masks_parent1);
             allowed_parent2 = scope_to_request(
                 access_request_parent2, layer_masks_parent2);
 
             /* Stops when all accesses are granted. */
             if (allowed_parent1 && allowed_parent2)
                 break;
 
             /*
              * Now, downgrades the remaining checks from domain
              * handled accesses to requested accesses.
              */
             is_dom_check = false;
             access_masked_parent1 = access_request_parent1;
             access_masked_parent2 = access_request_parent2;
         }
 
         rule = find_rule(domain, walker_path.dentry);
         allowed_parent1 = unmask_layers(rule, access_masked_parent1,
                         layer_masks_parent1);
         allowed_parent2 = unmask_layers(rule, access_masked_parent2,
                         layer_masks_parent2);
 
         /* Stops when a rule from each layer grants access. */
         if (allowed_parent1 && allowed_parent2)
             break;
 
 jump_up:
         if (walker_path.dentry == walker_path.mnt->mnt_root) {
             if (follow_up(&walker_path)) {
                 /* Ignores hidden mount points. */
                 goto jump_up;
             } else {
                 /*
                  * Stops at the real root.  Denies access
                  * because not all layers have granted access.
                  */
                 break;
             }
         }
         if (unlikely(IS_ROOT(walker_path.dentry))) {
             /*
              * Stops at disconnected root directories.  Only allows
              * access to internal filesystems (e.g. nsfs, which is
              * reachable through /proc/<pid>/ns/<namespace>).
              */
             allowed_parent1 = allowed_parent2 =
                 !!(walker_path.mnt->mnt_flags & MNT_INTERNAL);
             break;
         }
         parent_dentry = dget_parent(walker_path.dentry);
         dput(walker_path.dentry);
         walker_path.dentry = parent_dentry;
     }
     path_put(&walker_path);
 
     if (allowed_parent1 && allowed_parent2)
         return 0;
 
     /*
      * This prioritizes EACCES over EXDEV for all actions, including
      * renames with RENAME_EXCHANGE.
      */
     if (likely(is_eacces(layer_masks_parent1, access_request_parent1) ||
            is_eacces(layer_masks_parent2, access_request_parent2)))
         return -EACCES;
 
     /*
      * Gracefully forbids reparenting if the destination directory
      * hierarchy is not a superset of restrictions of the source directory
      * hierarchy, or if LANDLOCK_ACCESS_FS_REFER is not allowed by the
      * source or the destination.
      */
     return -EXDEV;
 }
 
 static inline int check_access_path(const struct landlock_ruleset *const domain,
                     const struct path *const path,
                     access_mask_t access_request)
 {
     layer_mask_t layer_masks[LANDLOCK_NUM_ACCESS_FS] = {};
 
     access_request = init_layer_masks(domain, access_request, &layer_masks);
     return check_access_path_dual(domain, path, access_request,
                       &layer_masks, NULL, 0, NULL, NULL);
 }
 
 static inline int current_check_access_path(const struct path *const path,
                         const access_mask_t access_request)
 {
     const struct landlock_ruleset *const dom =
         landlock_get_current_domain();
 
     if (!dom)
         return 0;
     return check_access_path(dom, path, access_request);
 }
 
 static inline access_mask_t get_mode_access(const umode_t mode)
 {
     switch (mode & S_IFMT) {
     case S_IFLNK:
         return LANDLOCK_ACCESS_FS_MAKE_SYM;
     case 0:
         /* A zero mode translates to S_IFREG. */
     case S_IFREG:
         return LANDLOCK_ACCESS_FS_MAKE_REG;
     case S_IFDIR:
         return LANDLOCK_ACCESS_FS_MAKE_DIR;
     case S_IFCHR:
         return LANDLOCK_ACCESS_FS_MAKE_CHAR;
     case S_IFBLK:
         return LANDLOCK_ACCESS_FS_MAKE_BLOCK;
     case S_IFIFO:
         return LANDLOCK_ACCESS_FS_MAKE_FIFO;
     case S_IFSOCK:
         return LANDLOCK_ACCESS_FS_MAKE_SOCK;
     default:
         WARN_ON_ONCE(1);
         return 0;
     }
 }
 
 static inline access_mask_t maybe_remove(const struct dentry *const dentry)
 {
     if (d_is_negative(dentry))
         return 0;
     return d_is_dir(dentry) ? LANDLOCK_ACCESS_FS_REMOVE_DIR :
                   LANDLOCK_ACCESS_FS_REMOVE_FILE;
 }
 
 /**
  * collect_domain_accesses - Walk through a file path and collect accesses
  *
  * @domain: Domain to check against.
  * @mnt_root: Last directory to check.
  * @dir: Directory to start the walk from.
  * @layer_masks_dom: Where to store the collected accesses.
  *
  * This helper is useful to begin a path walk from the @dir directory to a
  * @mnt_root directory used as a mount point.  This mount point is the common
  * ancestor between the source and the destination of a renamed and linked
  * file.  While walking from @dir to @mnt_root, we record all the domain's
  * allowed accesses in @layer_masks_dom.
  *
  * This is similar to check_access_path_dual() but much simpler because it only
  * handles walking on the same mount point and only check one set of accesses.
  *
  * Returns:
  * - true if all the domain access rights are allowed for @dir;
  * - false if the walk reached @mnt_root.
  */
 static bool collect_domain_accesses(
     const struct landlock_ruleset *const domain,
     const struct dentry *const mnt_root, struct dentry *dir,
     layer_mask_t (*const layer_masks_dom)[LANDLOCK_NUM_ACCESS_FS])
 {
     unsigned long access_dom;
     bool ret = false;
 
     if (WARN_ON_ONCE(!domain || !mnt_root || !dir || !layer_masks_dom))
         return true;
     if (is_nouser_or_private(dir))
         return true;
 
     access_dom = init_layer_masks(domain, LANDLOCK_MASK_ACCESS_FS,
                       layer_masks_dom);
 
     dget(dir);
     while (true) {
         struct dentry *parent_dentry;
 
         /* Gets all layers allowing all domain accesses. */
         if (unmask_layers(find_rule(domain, dir), access_dom,
                   layer_masks_dom)) {
             /*
              * Stops when all handled accesses are allowed by at
              * least one rule in each layer.
              */
             ret = true;
             break;
         }
 
         /* We should not reach a root other than @mnt_root. */
         if (dir == mnt_root || WARN_ON_ONCE(IS_ROOT(dir)))
             break;
 
         parent_dentry = dget_parent(dir);
         dput(dir);
         dir = parent_dentry;
     }
     dput(dir);
     return ret;
 }
 
 /**
  * current_check_refer_path - Check if a rename or link action is allowed
  *
  * @old_dentry: File or directory requested to be moved or linked.
  * @new_dir: Destination parent directory.
  * @new_dentry: Destination file or directory.
  * @removable: Sets to true if it is a rename operation.
  * @exchange: Sets to true if it is a rename operation with RENAME_EXCHANGE.
  *
  * Because of its unprivileged constraints, Landlock relies on file hierarchies
  * (and not only inodes) to tie access rights to files.  Being able to link or
  * rename a file hierarchy brings some challenges.  Indeed, moving or linking a
  * file (i.e. creating a new reference to an inode) can have an impact on the
  * actions allowed for a set of files if it would change its parent directory
  * (i.e. reparenting).
  *
  * To avoid trivial access right bypasses, Landlock first checks if the file or
  * directory requested to be moved would gain new access rights inherited from
  * its new hierarchy.  Before returning any error, Landlock then checks that
  * the parent source hierarchy and the destination hierarchy would allow the
  * link or rename action.  If it is not the case, an error with EACCES is
  * returned to inform user space that there is no way to remove or create the
  * requested source file type.  If it should be allowed but the new inherited
  * access rights would be greater than the source access rights, then the
  * kernel returns an error with EXDEV.  Prioritizing EACCES over EXDEV enables
  * user space to abort the whole operation if there is no way to do it, or to
  * manually copy the source to the destination if this remains allowed, e.g.
  * because file creation is allowed on the destination directory but not direct
  * linking.
  *
  * To achieve this goal, the kernel needs to compare two file hierarchies: the
  * one identifying the source file or directory (including itself), and the
  * destination one.  This can be seen as a multilayer partial ordering problem.
  * The kernel walks through these paths and collects in a matrix the access
  * rights that are denied per layer.  These matrices are then compared to see
  * if the destination one has more (or the same) restrictions as the source
  * one.  If this is the case, the requested action will not return EXDEV, which
  * doesn't mean the action is allowed.  The parent hierarchy of the source
  * (i.e. parent directory), and the destination hierarchy must also be checked
  * to verify that they explicitly allow such action (i.e.  referencing,
  * creation and potentially removal rights).  The kernel implementation is then
  * required to rely on potentially four matrices of access rights: one for the
  * source file or directory (i.e. the child), a potentially other one for the
  * other source/destination (in case of RENAME_EXCHANGE), one for the source
  * parent hierarchy and a last one for the destination hierarchy.  These
  * ephemeral matrices take some space on the stack, which limits the number of
  * layers to a deemed reasonable number: 16.
  *
  * Returns:
  * - 0 if access is allowed;
  * - -EXDEV if @old_dentry would inherit new access rights from @new_dir;
  * - -EACCES if file removal or creation is denied.
  */
 static int current_check_refer_path(struct dentry *const old_dentry,
                     const struct path *const new_dir,
                     struct dentry *const new_dentry,
                     const bool removable, const bool exchange)
 {
     const struct landlock_ruleset *const dom =
         landlock_get_current_domain();
     bool allow_parent1, allow_parent2;
     access_mask_t access_request_parent1, access_request_parent2;
     struct path mnt_dir;
     layer_mask_t layer_masks_parent1[LANDLOCK_NUM_ACCESS_FS],
         layer_masks_parent2[LANDLOCK_NUM_ACCESS_FS];
 
     if (!dom)
         return 0;
     if (WARN_ON_ONCE(dom->num_layers < 1))
         return -EACCES;
     if (unlikely(d_is_negative(old_dentry)))
         return -ENOENT;
     if (exchange) {
         if (unlikely(d_is_negative(new_dentry)))
             return -ENOENT;
         access_request_parent1 =
             get_mode_access(d_backing_inode(new_dentry)->i_mode);
     } else {
         access_request_parent1 = 0;
     }
     access_request_parent2 =
         get_mode_access(d_backing_inode(old_dentry)->i_mode);
     if (removable) {
         access_request_parent1 |= maybe_remove(old_dentry);
         access_request_parent2 |= maybe_remove(new_dentry);
     }
 
     /* The mount points are the same for old and new paths, cf. EXDEV. */
     if (old_dentry->d_parent == new_dir->dentry) {
         /*
          * The LANDLOCK_ACCESS_FS_REFER access right is not required
          * for same-directory referer (i.e. no reparenting).
          */
         access_request_parent1 = init_layer_masks(
             dom, access_request_parent1 | access_request_parent2,
             &layer_masks_parent1);
         return check_access_path_dual(dom, new_dir,
                           access_request_parent1,
                           &layer_masks_parent1, NULL, 0,
                           NULL, NULL);
     }
 
     access_request_parent1 |= LANDLOCK_ACCESS_FS_REFER;
     access_request_parent2 |= LANDLOCK_ACCESS_FS_REFER;
 
     /* Saves the common mount point. */
     mnt_dir.mnt = new_dir->mnt;
     mnt_dir.dentry = new_dir->mnt->mnt_root;
 
     /* new_dir->dentry is equal to new_dentry->d_parent */
     allow_parent1 = collect_domain_accesses(dom, mnt_dir.dentry,
                         old_dentry->d_parent,
                         &layer_masks_parent1);
     allow_parent2 = collect_domain_accesses(
         dom, mnt_dir.dentry, new_dir->dentry, &layer_masks_parent2);
 
     if (allow_parent1 && allow_parent2)
         return 0;
 
     /*
      * To be able to compare source and destination domain access rights,
      * take into account the @old_dentry access rights aggregated with its
      * parent access rights.  This will be useful to compare with the
      * destination parent access rights.
      */
     return check_access_path_dual(dom, &mnt_dir, access_request_parent1,
                       &layer_masks_parent1, old_dentry,
                       access_request_parent2,
                       &layer_masks_parent2,
                       exchange ? new_dentry : NULL);
 }
 
 /* Inode hooks */
 
 static void hook_inode_free_security(struct inode *const inode)
 {
     /*
      * All inodes must already have been untied from their object by
      * release_inode() or hook_sb_delete().
      */
     WARN_ON_ONCE(landlock_inode(inode)->object);
 }
 
 /* Super-block hooks */
 
 /*
  * Release the inodes used in a security policy.
  *
  * Cf. fsnotify_unmount_inodes() and invalidate_inodes()
  */
 static void hook_sb_delete(struct super_block *const sb)
 {
     struct inode *inode, *prev_inode = NULL;
 
     if (!landlock_initialized)
         return;
 
     spin_lock(&sb->s_inode_list_lock);
     list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
         struct landlock_object *object;
 
         /* Only handles referenced inodes. */
         if (!atomic_read(&inode->i_count))
             continue;
 
         /*
          * Protects against concurrent modification of inode (e.g.
          * from get_inode_object()).
          */
         spin_lock(&inode->i_lock);
         /*
          * Checks I_FREEING and I_WILL_FREE  to protect against a race
          * condition when release_inode() just called iput(), which
          * could lead to a NULL dereference of inode->security or a
          * second call to iput() for the same Landlock object.  Also
          * checks I_NEW because such inode cannot be tied to an object.
          */
         if (inode->i_state & (I_FREEING | I_WILL_FREE | I_NEW)) {
             spin_unlock(&inode->i_lock);
             continue;
         }
 
         rcu_read_lock();
         object = rcu_dereference(landlock_inode(inode)->object);
         if (!object) {
             rcu_read_unlock();
             spin_unlock(&inode->i_lock);
             continue;
         }
         /* Keeps a reference to this inode until the next loop walk. */
         __iget(inode);
         spin_unlock(&inode->i_lock);
 
         /*
          * If there is no concurrent release_inode() ongoing, then we
          * are in charge of calling iput() on this inode, otherwise we
          * will just wait for it to finish.
          */
         spin_lock(&object->lock);
         if (object->underobj == inode) {
             object->underobj = NULL;
             spin_unlock(&object->lock);
             rcu_read_unlock();
 
             /*
              * Because object->underobj was not NULL,
              * release_inode() and get_inode_object() guarantee
              * that it is safe to reset
              * landlock_inode(inode)->object while it is not NULL.
              * It is therefore not necessary to lock inode->i_lock.
              */
             rcu_assign_pointer(landlock_inode(inode)->object, NULL);
             /*
              * At this point, we own the ihold() reference that was
              * originally set up by get_inode_object() and the
              * __iget() reference that we just set in this loop
              * walk.  Therefore the following call to iput() will
              * not sleep nor drop the inode because there is now at
              * least two references to it.
              */
             iput(inode);
         } else {
             spin_unlock(&object->lock);
             rcu_read_unlock();
         }
 
         if (prev_inode) {
             /*
              * At this point, we still own the __iget() reference
              * that we just set in this loop walk.  Therefore we
              * can drop the list lock and know that the inode won't
              * disappear from under us until the next loop walk.
              */
             spin_unlock(&sb->s_inode_list_lock);
             /*
              * We can now actually put the inode reference from the
              * previous loop walk, which is not needed anymore.
              */
             iput(prev_inode);
             cond_resched();
             spin_lock(&sb->s_inode_list_lock);
         }
         prev_inode = inode;
     }
     spin_unlock(&sb->s_inode_list_lock);
 
     /* Puts the inode reference from the last loop walk, if any. */
     if (prev_inode)
         iput(prev_inode);
     /* Waits for pending iput() in release_inode(). */
     wait_var_event(&landlock_superblock(sb)->inode_refs,
                !atomic_long_read(&landlock_superblock(sb)->inode_refs));
 }
 
 /*
  * Because a Landlock security policy is defined according to the filesystem
  * topology (i.e. the mount namespace), changing it may grant access to files
  * not previously allowed.
  *
  * To make it simple, deny any filesystem topology modification by landlocked
  * processes.  Non-landlocked processes may still change the namespace of a
  * landlocked process, but this kind of threat must be handled by a system-wide
  * access-control security policy.
  *
  * This could be lifted in the future if Landlock can safely handle mount
  * namespace updates requested by a landlocked process.  Indeed, we could
  * update the current domain (which is currently read-only) by taking into
  * account the accesses of the source and the destination of a new mount point.
  * However, it would also require to make all the child domains dynamically
  * inherit these new constraints.  Anyway, for backward compatibility reasons,
  * a dedicated user space option would be required (e.g. as a ruleset flag).
  */
 static int hook_sb_mount(const char *const dev_name,
              const struct path *const path, const char *const type,
              const unsigned long flags, void *const data)
 {
     if (!landlock_get_current_domain())
         return 0;
     return -EPERM;
 }
 
 static int hook_move_mount(const struct path *const from_path,
                const struct path *const to_path)
 {
     if (!landlock_get_current_domain())
         return 0;
     return -EPERM;
 }
 
 /*
  * Removing a mount point may reveal a previously hidden file hierarchy, which
  * may then grant access to files, which may have previously been forbidden.
  */
 static int hook_sb_umount(struct vfsmount *const mnt, const int flags)
 {
     if (!landlock_get_current_domain())
         return 0;
     return -EPERM;
 }
 
 static int hook_sb_remount(struct super_block *const sb, void *const mnt_opts)
 {
     if (!landlock_get_current_domain())
         return 0;
     return -EPERM;
 }
 
 /*
  * pivot_root(2), like mount(2), changes the current mount namespace.  It must
  * then be forbidden for a landlocked process.
  *
  * However, chroot(2) may be allowed because it only changes the relative root
  * directory of the current process.  Moreover, it can be used to restrict the
  * view of the filesystem.
  */
 static int hook_sb_pivotroot(const struct path *const old_path,
                  const struct path *const new_path)
 {
     if (!landlock_get_current_domain())
         return 0;
     return -EPERM;
 }
 
 /* Path hooks */
 
 static int hook_path_link(struct dentry *const old_dentry,
               const struct path *const new_dir,
               struct dentry *const new_dentry)
 {
     return current_check_refer_path(old_dentry, new_dir, new_dentry, false,
                     false);
 }
 
 static int hook_path_rename(const struct path *const old_dir,
                 struct dentry *const old_dentry,
                 const struct path *const new_dir,
                 struct dentry *const new_dentry,
                 const unsigned int flags)
 {
     /* old_dir refers to old_dentry->d_parent and new_dir->mnt */
     return current_check_refer_path(old_dentry, new_dir, new_dentry, true,
                     !!(flags & RENAME_EXCHANGE));
 }
 
 static int hook_path_mkdir(const struct path *const dir,
                struct dentry *const dentry, const umode_t mode)
 {
     return current_check_access_path(dir, LANDLOCK_ACCESS_FS_MAKE_DIR);
 }
 
 static int hook_path_mknod(const struct path *const dir,
                struct dentry *const dentry, const umode_t mode,
                const unsigned int dev)
 {
     const struct landlock_ruleset *const dom =
         landlock_get_current_domain();
 
     if (!dom)
         return 0;
     return check_access_path(dom, dir, get_mode_access(mode));
 }
 
 static int hook_path_symlink(const struct path *const dir,
                  struct dentry *const dentry,
                  const char *const old_name)
 {
     return current_check_access_path(dir, LANDLOCK_ACCESS_FS_MAKE_SYM);
 }
 
 static int hook_path_unlink(const struct path *const dir,
                 struct dentry *const dentry)
 {
     return current_check_access_path(dir, LANDLOCK_ACCESS_FS_REMOVE_FILE);
 }
 
 static int hook_path_rmdir(const struct path *const dir,
                struct dentry *const dentry)
 {
     return current_check_access_path(dir, LANDLOCK_ACCESS_FS_REMOVE_DIR);
 }
 
 /* File hooks */
 
 static inline access_mask_t get_file_access(const struct file *const file)
 {
     access_mask_t access = 0;
 
     if (file->f_mode & FMODE_READ) {
         /* A directory can only be opened in read mode. */
         if (S_ISDIR(file_inode(file)->i_mode))
             return LANDLOCK_ACCESS_FS_READ_DIR;
         access = LANDLOCK_ACCESS_FS_READ_FILE;
     }
     if (file->f_mode & FMODE_WRITE)
         access |= LANDLOCK_ACCESS_FS_WRITE_FILE;
     /* __FMODE_EXEC is indeed part of f_flags, not f_mode. */
     if (file->f_flags & __FMODE_EXEC)
         access |= LANDLOCK_ACCESS_FS_EXECUTE;
     return access;
 }
 
 static int hook_file_open(struct file *const file)
 {
     const struct landlock_ruleset *const dom =
         landlock_get_current_domain();
 
     if (!dom)
         return 0;
     /*
      * Because a file may be opened with O_PATH, get_file_access() may
      * return 0.  This case will be handled with a future Landlock
      * evolution.
      */
     return check_access_path(dom, &file->f_path, get_file_access(file));
 }
 
 static struct security_hook_list landlock_hooks[] __lsm_ro_after_init = {
     LSM_HOOK_INIT(inode_free_security, hook_inode_free_security),
 
     LSM_HOOK_INIT(sb_delete, hook_sb_delete),
     LSM_HOOK_INIT(sb_mount, hook_sb_mount),
     LSM_HOOK_INIT(move_mount, hook_move_mount),
     LSM_HOOK_INIT(sb_umount, hook_sb_umount),
     LSM_HOOK_INIT(sb_remount, hook_sb_remount),
     LSM_HOOK_INIT(sb_pivotroot, hook_sb_pivotroot),
 
     LSM_HOOK_INIT(path_link, hook_path_link),
     LSM_HOOK_INIT(path_rename, hook_path_rename),
     LSM_HOOK_INIT(path_mkdir, hook_path_mkdir),
     LSM_HOOK_INIT(path_mknod, hook_path_mknod),
     LSM_HOOK_INIT(path_symlink, hook_path_symlink),
     LSM_HOOK_INIT(path_unlink, hook_path_unlink),
     LSM_HOOK_INIT(path_rmdir, hook_path_rmdir),
 
     LSM_HOOK_INIT(file_open, hook_file_open),
 };
 
 __init void landlock_add_fs_hooks(void)
 {
     security_add_hooks(landlock_hooks, ARRAY_SIZE(landlock_hooks),
                LANDLOCK_NAME);
 }

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