landlock: Create find_rule() from unmask_layers()

This refactoring will be useful in a following commit.

Reviewed-by: Paul Moore <paul@paul-moore.com>
Link: https://lore.kernel.org/r/20220506161102.525323-4-mic@digikod.net
Cc: stable@vger.kernel.org
Signed-off-by: Mickaël Salaün <mic@digikod.net>

diff --git a/security/landlock/fs.c b/security/landlock/fs.c
index f48c0a3..20953bf 100644 (file)
--- a/security/landlock/fs.c
+++ b/security/landlock/fs.c
@@ -183,23 +183,36 @@ int landlock_append_fs_rule(struct landlock_ruleset *const ruleset,
 
 /* Access-control management */
 
-static inline layer_mask_t
-unmask_layers(const struct landlock_ruleset *const domain,
-             const struct path *const path, const access_mask_t access_request,
-             layer_mask_t layer_mask)
+/*
+ * 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;
-       size_t i;
 
-       if (d_is_negative(path->dentry))
-               /* Ignore nonexistent leafs. */
-               return layer_mask;
-       inode = d_backing_inode(path->dentry);
+       /* 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;
+}
+
+static inline layer_mask_t unmask_layers(const struct landlock_rule *const rule,
+                                        const access_mask_t access_request,
+                                        layer_mask_t layer_mask)
+{
+       size_t layer_level;
+
        if (!rule)
                return layer_mask;
 
@@ -210,8 +223,9 @@ unmask_layers(const struct landlock_ruleset *const domain,
         * the remaining layers for each inode, from the first added layer to
         * the last one.
         */
-       for (i = 0; i < rule->num_layers; i++) {
-               const struct landlock_layer *const layer = &rule->layers[i];
+       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);
 
                /* Checks that the layer grants access to the full request. */
@@ -269,8 +283,9 @@ static int check_access_path(const struct landlock_ruleset *const domain,
        while (true) {
                struct dentry *parent_dentry;
 
-               layer_mask = unmask_layers(domain, &walker_path, access_request,
-                                          layer_mask);
+               layer_mask =
+                       unmask_layers(find_rule(domain, walker_path.dentry),
+                                     access_request, layer_mask);
                if (layer_mask == 0) {
                        /* Stops when a rule from each layer grants access. */
                        allowed = true;