crypto: af_alg - Disallow bind/setkey/... after accept(2)

commit c840ac6af3f8713a71b4d2363419145760bd6044 upstream.

Each af_alg parent socket obtained by socket(2) corresponds to a
tfm object once bind(2) has succeeded.  An accept(2) call on that
parent socket creates a context which then uses the tfm object.

Therefore as long as any child sockets created by accept(2) exist
the parent socket must not be modified or freed.

This patch guarantees this by using locks and a reference count
on the parent socket.  Any attempt to modify the parent socket will
fail with EBUSY.

Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

1 files changed, 32 insertions, 3 deletions

diff --git a/crypto/af_alg.c b/crypto/af_alg.c
index 1de4beeb25f8..abb828a3e424 100644
--- a/crypto/af_alg.c
+++ b/crypto/af_alg.c
@@ -125,6 +125,23 @@ int af_alg_release(struct socket *sock)
 }
 EXPORT_SYMBOL_GPL(af_alg_release);
 
+void af_alg_release_parent(struct sock *sk)
+{
+	struct alg_sock *ask = alg_sk(sk);
+	bool last;
+
+	sk = ask->parent;
+	ask = alg_sk(sk);
+
+	lock_sock(sk);
+	last = !--ask->refcnt;
+	release_sock(sk);
+
+	if (last)
+		sock_put(sk);
+}
+EXPORT_SYMBOL_GPL(af_alg_release_parent);
+
 static int alg_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
 {
 	struct sock *sk = sock->sk;
@@ -132,6 +149,7 @@ static int alg_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
 	struct sockaddr_alg *sa = (void *)uaddr;
 	const struct af_alg_type *type;
 	void *private;
+	int err;
 
 	if (sock->state == SS_CONNECTED)
 		return -EINVAL;
@@ -157,16 +175,22 @@ static int alg_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
 		return PTR_ERR(private);
 	}
 
+	err = -EBUSY;
 	lock_sock(sk);
+	if (ask->refcnt)
+		goto unlock;
 
 	swap(ask->type, type);
 	swap(ask->private, private);
 
+	err = 0;
+
+unlock:
 	release_sock(sk);
 
 	alg_do_release(type, private);
 
-	return 0;
+	return err;
 }
 
 static int alg_setkey(struct sock *sk, char __user *ukey,
@@ -199,11 +223,15 @@ static int alg_setsockopt(struct socket *sock, int level, int optname,
 	struct sock *sk = sock->sk;
 	struct alg_sock *ask = alg_sk(sk);
 	const struct af_alg_type *type;
-	int err = -ENOPROTOOPT;
+	int err = -EBUSY;
 
 	lock_sock(sk);
+	if (ask->refcnt)
+		goto unlock;
+
 	type = ask->type;
 
+	err = -ENOPROTOOPT;
 	if (level != SOL_ALG || !type)
 		goto unlock;
 
@@ -254,7 +282,8 @@ int af_alg_accept(struct sock *sk, struct socket *newsock)
 
 	sk2->sk_family = PF_ALG;
 
-	sock_hold(sk);
+	if (!ask->refcnt++)
+		sock_hold(sk);
 	alg_sk(sk2)->parent = sk;
 	alg_sk(sk2)->type = type;