Re: [syzbot] [keyrings?] [lsm?] KASAN: slab-use-after-free Read in key_put

[Hillf Danton <hdanton@sina.com>]

On Mon, 18 Nov 2024 08:27:24 -0800
> syzbot found the following issue on:
> 
> HEAD commit:    adc218676eef Linux 6.12
> git tree:       upstream
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11c672e8580000

#syz test

--- x/security/keys/key.c
+++ y/security/keys/key.c
@@ -645,21 +645,30 @@ EXPORT_SYMBOL(key_reject_and_link);
  */
 void key_put(struct key *key)
 {
+	int quota_flag;
+	unsigned short len;
+	struct key_user *user;
+
 	if (key) {
 		key_check(key);
 
+		quota_flag = test_bit(KEY_FLAG_IN_QUOTA, &key->flags);
+		len = key->quotalen;
+		user = key->user;
+		refcount_inc(&user->usage);
 		if (refcount_dec_and_test(&key->usage)) {
 			unsigned long flags;
 
 			/* deal with the user's key tracking and quota */
-			if (test_bit(KEY_FLAG_IN_QUOTA, &key->flags)) {
-				spin_lock_irqsave(&key->user->lock, flags);
-				key->user->qnkeys--;
-				key->user->qnbytes -= key->quotalen;
-				spin_unlock_irqrestore(&key->user->lock, flags);
+			if (quota_flag) {
+				spin_lock_irqsave(&user->lock, flags);
+				user->qnkeys--;
+				user->qnbytes -= len;
+				spin_unlock_irqrestore(&user->lock, flags);
 			}
 			schedule_work(&key_gc_work);
 		}
+		key_user_put(user);
 	}
 }
 EXPORT_SYMBOL(key_put);
--