[PATCH 4.3 174/200] crypto: algif_skcipher - Fix race condition in skcipher_check_key

[Greg Kroah-Hartman]

4.3-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>

commit 1822793a523e5d5730b19cc21160ff1717421bc8 upstream.

We need to lock the child socket in skcipher_check_key as otherwise
two simultaneous calls can cause the parent socket to be freed.

Signed-off-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 crypto/algif_skcipher.c |    9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

--- a/crypto/algif_skcipher.c
+++ b/crypto/algif_skcipher.c
@@ -755,22 +755,23 @@ static struct proto_ops algif_skcipher_o
 
 static int skcipher_check_key(struct socket *sock)
 {
-	int err;
+	int err = 0;
 	struct sock *psk;
 	struct alg_sock *pask;
 	struct skcipher_tfm *tfm;
 	struct sock *sk = sock->sk;
 	struct alg_sock *ask = alg_sk(sk);
 
+	lock_sock(sk);
 	if (ask->refcnt)
-		return 0;
+		goto unlock_child;
 
 	psk = ask->parent;
 	pask = alg_sk(ask->parent);
 	tfm = pask->private;
 
 	err = -ENOKEY;
-	lock_sock(psk);
+	lock_sock_nested(psk, SINGLE_DEPTH_NESTING);
 	if (!tfm->has_key)
 		goto unlock;
 
@@ -784,6 +785,8 @@ static int skcipher_check_key(struct soc
 
 unlock:
 	release_sock(psk);
+unlock_child:
+	release_sock(sk);
 
 	return err;
 }