[3.16.y-ckt stable] Patch "crypto: af_alg - Disallow bind/setkey/... after accept(2)" has been added to the 3.16.y-ckt tree

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

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

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt24.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

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

>From 529382a7cc33f5e12f54e44caa2bf09a5ad1fec0 Mon Sep 17 00:00:00 2001
From: Herbert Xu <herbert at gondor.apana.org.au>
Date: Wed, 30 Dec 2015 11:47:53 +0800
Subject: 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 at google.com>
Signed-off-by: Herbert Xu <herbert at gondor.apana.org.au>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 crypto/af_alg.c         | 35 ++++++++++++++++++++++++++++++++---
 include/crypto/if_alg.h |  8 +++-----
 2 files changed, 35 insertions(+), 8 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;

diff --git a/include/crypto/if_alg.h b/include/crypto/if_alg.h
index d61c11170213..2f38daaab3d7 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;
 };
@@ -64,6 +66,7 @@ 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, void __user *addr, int len,
@@ -80,11 +83,6 @@ 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);