Re: [PATCH v8 3/9] landlock: Refactor check_access_path_dual() into is_access_to_paths_allowed()

Mickaël Salaün <mic@xxxxxxxxxxx> · Wed, 5 Oct 2022 20:54:08 +0200

Great!

On 01/10/2022 17:49, Günther Noack wrote:
* Rename it 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

Can you please replace these bullet points with (one-sentence) paragraphs?



Suggested-by: Mickaël Salaün <mic@xxxxxxxxxxx>
Signed-off-by: Günther Noack <gnoack3000@xxxxxxxxx>
---
  security/landlock/fs.c | 89 +++++++++++++++++++++---------------------
  1 file changed, 44 insertions(+), 45 deletions(-)

diff --git a/security/landlock/fs.c b/security/landlock/fs.c
index a9dbd99d9ee7..083dd3d359de 100644
--- a/security/landlock/fs.c
+++ b/security/landlock/fs.c
@@ -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

Missing final dot.


   */
-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 check 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 */






