Merge tag 'keys-next-6.14-rc8' of git://git.kernel.org/pub/scm/linux/kernel/git/jarkko/linux-tpmdd

Pull keys fix from Jarkko Sakkinen:
 "Fix potential use-after-free in key_put()"

* tag 'keys-next-6.14-rc8' of git://git.kernel.org/pub/scm/linux/kernel/git/jarkko/linux-tpmdd:
  keys: Fix UAF in key_put()

3 files changed, 6 insertions, 1 deletions

diff --git a/include/linux/key.h b/include/linux/key.h
index 074dca3222b9..ba05de8579ec 100644
--- a/include/linux/key.h
+++ b/include/linux/key.h
@@ -236,6 +236,7 @@ struct key {
 #define KEY_FLAG_ROOT_CAN_INVAL	7	/* set if key can be invalidated by root without permission */
 #define KEY_FLAG_KEEP		8	/* set if key should not be removed */
 #define KEY_FLAG_UID_KEYRING	9	/* set if key is a user or user session keyring */
+#define KEY_FLAG_FINAL_PUT	10	/* set if final put has happened on key */
 
 	/* the key type and key description string
 	 * - the desc is used to match a key against search criteria
diff --git a/security/keys/gc.c b/security/keys/gc.c
index 7d687b0962b1..f27223ea4578 100644
--- a/security/keys/gc.c
+++ b/security/keys/gc.c
@@ -218,8 +218,10 @@ continue_scanning:
 		key = rb_entry(cursor, struct key, serial_node);
 		cursor = rb_next(cursor);
 
-		if (refcount_read(&key->usage) == 0)
+		if (test_bit(KEY_FLAG_FINAL_PUT, &key->flags)) {
+			smp_mb(); /* Clobber key->user after FINAL_PUT seen. */
 			goto found_unreferenced_key;
+		}
 
 		if (unlikely(gc_state & KEY_GC_REAPING_DEAD_1)) {
 			if (key->type == key_gc_dead_keytype) {
diff --git a/security/keys/key.c b/security/keys/key.c
index 3d7d185019d3..7198cd2ac3a3 100644
--- a/security/keys/key.c
+++ b/security/keys/key.c
@@ -658,6 +658,8 @@ void key_put(struct key *key)
 				key->user->qnbytes -= key->quotalen;
 				spin_unlock_irqrestore(&key->user->lock, flags);
 			}
+			smp_mb(); /* key->user before FINAL_PUT set. */
+			set_bit(KEY_FLAG_FINAL_PUT, &key->flags);
 			schedule_work(&key_gc_work);
 		}
 	}