1 files changed, 22 insertions, 19 deletions

diff --git a/security/keys/keyring.c b/security/keys/keyring.c
index 29de5ee3457b..3f425a65906f 100644
--- a/security/keys/keyring.c
+++ b/security/keys/keyring.c
@@ -20,6 +20,11 @@
 #include <linux/uaccess.h>
 #include "internal.h"
 
+#define rcu_dereference_locked_keyring(keyring)                         \
+        (rcu_dereference_protected(                                     \
+                (keyring)->payload.subscriptions,                       \
+                rwsem_is_locked((struct rw_semaphore *)&(keyring)->sem)))
+
 /*
  * when plumbing the depths of the key tree, this sets a hard limit set on how
  * deep we're willing to go
@@ -199,8 +204,7 @@ static long keyring_read(const struct key *keyring,
         int loop, ret;
 
         ret = 0;
-        klist = keyring->payload.subscriptions;
-
+        klist = rcu_dereference_locked_keyring(keyring);
         if (klist) {
                 /* calculate how much data we could return */
                 qty = klist->nkeys * sizeof(key_serial_t);
@@ -524,9 +528,8 @@ struct key *find_keyring_by_name(const char *name, bool skip_perm_check)
         struct key *keyring;
         int bucket;
 
-        keyring = ERR_PTR(-EINVAL);
         if (!name)
-                goto error;
+                return ERR_PTR(-EINVAL);
 
         bucket = keyring_hash(name);
 
@@ -553,17 +556,18 @@ struct key *find_keyring_by_name(const char *name, bool skip_perm_check)
                                            KEY_SEARCH) < 0)
                                 continue;
 
-                        /* we've got a match */
-                        atomic_inc(&keyring->usage);
-                        read_unlock(&keyring_name_lock);
-                        goto error;
+                        /* we've got a match but we might end up racing with
+                         * key_cleanup() if the keyring is currently 'dead'
+                         * (ie. it has a zero usage count) */
+                        if (!atomic_inc_not_zero(&keyring->usage))
+                                continue;
+                        goto out;
                 }
         }
 
-        read_unlock(&keyring_name_lock);
         keyring = ERR_PTR(-ENOKEY);
-
-error:
+out:
+        read_unlock(&keyring_name_lock);
         return keyring;
 
 } /* end find_keyring_by_name() */
@@ -719,8 +723,7 @@ int __key_link(struct key *keyring, struct key *key)
         }
 
         /* see if there's a matching key we can displace */
-        klist = keyring->payload.subscriptions;
-
+        klist = rcu_dereference_locked_keyring(keyring);
         if (klist && klist->nkeys > 0) {
                 struct key_type *type = key->type;
 
@@ -764,8 +767,6 @@ int __key_link(struct key *keyring, struct key *key)
         if (ret < 0)
                 goto error2;
 
-        klist = keyring->payload.subscriptions;
-
         if (klist && klist->nkeys < klist->maxkeys) {
                 /* there's sufficient slack space to add directly */
                 atomic_inc(&key->usage);
@@ -867,7 +868,7 @@ int key_unlink(struct key *keyring, struct key *key)
 
         down_write(&keyring->sem);
 
-        klist = keyring->payload.subscriptions;
+        klist = rcu_dereference_locked_keyring(keyring);
         if (klist) {
                 /* search the keyring for the key */
                 for (loop = 0; loop < klist->nkeys; loop++)
@@ -958,7 +959,7 @@ int keyring_clear(struct key *keyring)
                 /* detach the pointer block with the locks held */
                 down_write(&keyring->sem);
 
-                klist = keyring->payload.subscriptions;
+                klist = rcu_dereference_locked_keyring(keyring);
                 if (klist) {
                         /* adjust the quota */
                         key_payload_reserve(keyring,
@@ -990,7 +991,9 @@ EXPORT_SYMBOL(keyring_clear);
  */
 static void keyring_revoke(struct key *keyring)
 {
-        struct keyring_list *klist = keyring->payload.subscriptions;
+        struct keyring_list *klist;
+
+        klist = rcu_dereference_locked_keyring(keyring);
 
         /* adjust the quota */
         key_payload_reserve(keyring, 0);
@@ -1024,7 +1027,7 @@ void keyring_gc(struct key *keyring, time_t limit)
 
         down_write(&keyring->sem);
 
-        klist = keyring->payload.subscriptions;
+        klist = rcu_dereference_locked_keyring(keyring);
         if (!klist)
                 goto no_klist;