linux-kernel - [PATCH 3.16.y-ckt 052/129] crypto: algif_skcipher - Fix race condition in skcipher_check

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Message-Id: <1456482100-4667-53-git-send-email-luis.henriques@canonical.com>
Date:	Fri, 26 Feb 2016 10:20:23 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Herbert Xu <herbert@...dor.apana.org.au>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 052/129] crypto: algif_skcipher - Fix race condition in skcipher_check_key

3.16.7-ckt25 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Herbert Xu <herbert@...dor.apana.org.au>

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@...dor.apana.org.au>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 crypto/algif_skcipher.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/crypto/algif_skcipher.c b/crypto/algif_skcipher.c
index de514c5d4503..45fa6bd9187b 100644
--- a/crypto/algif_skcipher.c
+++ b/crypto/algif_skcipher.c
@@ -551,22 +551,23 @@ static struct proto_ops algif_skcipher_ops = {
 
 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;
 
@@ -580,6 +581,8 @@ static int skcipher_check_key(struct socket *sock)
 
 unlock:
 	release_sock(psk);
+unlock_child:
+	release_sock(sk);
 
 	return err;
 }