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

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.

Cc: stable@vger.kernel.org
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

2 files changed, 35 insertions, 8 deletions

diff --git a/crypto/af_alg.c b/crypto/af_alg.c
index a8e7aa3e257b..7b5b5926c767 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)
 {
 	const u32 forbidden = CRYPTO_ALG_INTERNAL;
@@ -133,6 +150,7 @@ 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;
@@ -160,16 +178,22 @@ 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,
@@ -202,11 +226,15 @@ 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;
 
@@ -264,7 +292,8 @@ 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;
 
diff --git a/include/crypto/if_alg.h b/include/crypto/if_alg.h
index 018afb264ac2..589716f2ee8a 100644
--- a/include/crypto/if_alg.h
+++ b/include/crypto/if_alg.h
@@ -30,6 +30,8 @@ struct alg_sock {
 
 	struct sock *parent;
 
+	unsigned int refcnt;
+
 	const struct af_alg_type *type;
 	void *private;
 };
@@ -67,6 +69,7 @@ int af_alg_register_type(const struct af_alg_type *type);
 int af_alg_unregister_type(const struct af_alg_type *type);
 
 int af_alg_release(struct socket *sock);
+void af_alg_release_parent(struct sock *sk);
 int af_alg_accept(struct sock *sk, struct socket *newsock);
 
 int af_alg_make_sg(struct af_alg_sgl *sgl, struct iov_iter *iter, int len);
@@ -83,11 +86,6 @@ static inline struct alg_sock *alg_sk(struct sock *sk)
 	return (struct alg_sock *)sk;
 }
 
-static inline void af_alg_release_parent(struct sock *sk)
-{
-	sock_put(alg_sk(sk)->parent);
-}
-
 static inline void af_alg_init_completion(struct af_alg_completion *completion)
 {
 	init_completion(&completion->completion);