Unverified Commit 106794c4 authored by Günther Noack's avatar Günther Noack Committed by Mickaël Salaün
Browse files

landlock: Refactor check_access_path_dual() into is_access_to_paths_allowed() 



Rename check_access_path_dual() to is_access_to_paths_allowed().

Make it return true iff the access is allowed.

Calculate the EXDEV/EACCES error code in the one place where it's needed.

Suggested-by: default avatarMickaël Salaün <mic@digikod.net>
Signed-off-by: default avatarGünther Noack <gnoack3000@gmail.com>
Link: https://lore.kernel.org/r/20221018182216.301684-3-gnoack3000@gmail.com


Signed-off-by: default avatarMickaël Salaün <mic@digikod.net>
parent 3350607d

security/landlock/fs.c

+44 −45
Original line number Diff line number Diff line
@@ -430,7 +430,7 @@ is_eacces(const layer_mask_t (*const layer_masks)[LANDLOCK_NUM_ACCESS_FS], 
}



/**

 * check_access_path_dual - Check accesses for requests with a common path

 * is_access_to_paths_allowed - Check accesses for requests with a common path

 *

 * @domain: Domain to check against.

 * @path: File hierarchy to walk through.
@@ -465,14 +465,10 @@ is_eacces(const layer_mask_t (*const layer_masks)[LANDLOCK_NUM_ACCESS_FS], 
 * 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.

 * - true if the access request is granted;

 * - false otherwise.

 */

static int check_access_path_dual(

static bool is_access_to_paths_allowed(

	const struct landlock_ruleset *const domain,

	const struct path *const path,

	const access_mask_t access_request_parent1,
@@ -492,17 +488,17 @@ static int check_access_path_dual( 
	(*layer_masks_child2)[LANDLOCK_NUM_ACCESS_FS] = NULL;



	if (!access_request_parent1 && !access_request_parent2)

		return 0;

		return true;

	if (WARN_ON_ONCE(!domain || !path))

		return 0;

		return true;

	if (is_nouser_or_private(path->dentry))

		return 0;

		return true;

	if (WARN_ON_ONCE(domain->num_layers < 1 || !layer_masks_parent1))

		return -EACCES;

		return false;



	if (unlikely(layer_masks_parent2)) {

		if (WARN_ON_ONCE(!dentry_child1))

			return -EACCES;

			return false;

		/*

		 * For a double request, first check for potential privilege

		 * escalation by looking at domain handled accesses (which are
@@ -513,7 +509,7 @@ static int check_access_path_dual( 
		is_dom_check = true;

	} else {

		if (WARN_ON_ONCE(dentry_child1 || dentry_child2))

			return -EACCES;

			return false;

		/* For a simple request, only check for requested accesses. */

		access_masked_parent1 = access_request_parent1;

		access_masked_parent2 = access_request_parent2;
@@ -622,24 +618,7 @@ static int check_access_path_dual( 
	}

	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;

	return allowed_parent1 && allowed_parent2;

}



static inline int check_access_path(const struct landlock_ruleset *const domain,
@@ -649,8 +628,10 @@ static inline int check_access_path(const struct landlock_ruleset *const domain, 
	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);

	if (is_access_to_paths_allowed(domain, path, access_request,

				       &layer_masks, NULL, 0, NULL, NULL))

		return 0;

	return -EACCES;

}



static inline int current_check_access_path(const struct path *const path,
@@ -711,8 +692,9 @@ static inline access_mask_t maybe_remove(const struct dentry *const dentry) 
 * 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 checks one set of accesses.

 * This is similar to is_access_to_paths_allowed() but much simpler because it

 * only handles walking on the same mount point and only checks one set of

 * accesses.

 *

 * Returns:

 * - true if all the domain access rights are allowed for @dir;
@@ -857,10 +839,11 @@ static int current_check_refer_path(struct dentry *const old_dentry, 
		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);

		if (is_access_to_paths_allowed(

			    dom, new_dir, access_request_parent1,

			    &layer_masks_parent1, NULL, 0, NULL, NULL))

			return 0;

		return -EACCES;

	}



	access_request_parent1 |= LANDLOCK_ACCESS_FS_REFER;
@@ -886,11 +869,27 @@ static int current_check_refer_path(struct dentry *const old_dentry, 
	 * 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);

	if (is_access_to_paths_allowed(

		    dom, &mnt_dir, access_request_parent1, &layer_masks_parent1,

		    old_dentry, access_request_parent2, &layer_masks_parent2,

		    exchange ? new_dentry : NULL))

		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;

}



/* Inode hooks */