Commit 34c86f4c authored by Herbert Xu's avatar Herbert Xu
Browse files

crypto: af_alg - fix use-after-free in af_alg_accept() due to bh_lock_sock() 

The locking in af_alg_release_parent is broken as the BH socket
lock can only be taken if there is a code-path to handle the case
where the lock is owned by process-context.  Instead of adding
such handling, we can fix this by changing the ref counts to
atomic_t.

This patch also modifies the main refcnt to include both normal
and nokey sockets.  This way we don't have to fudge the nokey
ref count when a socket changes from nokey to normal.

Credits go to Mauricio Faria de Oliveira who diagnosed this bug
and sent a patch for it:

https://lore.kernel.org/linux-crypto/20200605161657.535043-1-mfo@canonical.com/



Reported-by: default avatarBrian Moyles <bmoyles@netflix.com>
Reported-by: default avatarMauricio Faria de Oliveira <mfo@canonical.com>
Fixes: 37f96694 ("crypto: af_alg - Use bh_lock_sock in...")
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
parent 819966c0

crypto/af_alg.c

+11 −15
Original line number Diff line number Diff line
@@ -128,21 +128,15 @@ EXPORT_SYMBOL_GPL(af_alg_release); 
void af_alg_release_parent(struct sock *sk)

{

	struct alg_sock *ask = alg_sk(sk);

	unsigned int nokey = ask->nokey_refcnt;

	bool last = nokey && !ask->refcnt;

	unsigned int nokey = atomic_read(&ask->nokey_refcnt);



	sk = ask->parent;

	ask = alg_sk(sk);



	local_bh_disable();

	bh_lock_sock(sk);

	ask->nokey_refcnt -= nokey;

	if (!last)

		last = !--ask->refcnt;

	bh_unlock_sock(sk);

	local_bh_enable();

	if (nokey)

		atomic_dec(&ask->nokey_refcnt);



	if (last)

	if (atomic_dec_and_test(&ask->refcnt))

		sock_put(sk);

}

EXPORT_SYMBOL_GPL(af_alg_release_parent);
@@ -187,7 +181,7 @@ static int alg_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len) 


	err = -EBUSY;

	lock_sock(sk);

	if (ask->refcnt | ask->nokey_refcnt)

	if (atomic_read(&ask->refcnt))

		goto unlock;



	swap(ask->type, type);
@@ -236,7 +230,7 @@ static int alg_setsockopt(struct socket *sock, int level, int optname, 
	int err = -EBUSY;



	lock_sock(sk);

	if (ask->refcnt)

	if (atomic_read(&ask->refcnt) != atomic_read(&ask->nokey_refcnt))

		goto unlock;



	type = ask->type;
@@ -301,12 +295,14 @@ int af_alg_accept(struct sock *sk, struct socket *newsock, bool kern) 
	if (err)

		goto unlock;



	if (nokey || !ask->refcnt++)

	if (atomic_inc_return_relaxed(&ask->refcnt) == 1)

		sock_hold(sk);

	ask->nokey_refcnt += nokey;

	if (nokey) {

		atomic_inc(&ask->nokey_refcnt);

		atomic_set(&alg_sk(sk2)->nokey_refcnt, 1);

	}

	alg_sk(sk2)->parent = sk;

	alg_sk(sk2)->type = type;

	alg_sk(sk2)->nokey_refcnt = nokey;



	newsock->ops = type->ops;

	newsock->state = SS_CONNECTED;

crypto/algif_aead.c

+3 −6
Original line number Diff line number Diff line
@@ -384,7 +384,7 @@ static int aead_check_key(struct socket *sock) 
	struct alg_sock *ask = alg_sk(sk);



	lock_sock(sk);

	if (ask->refcnt)

	if (!atomic_read(&ask->nokey_refcnt))

		goto unlock_child;



	psk = ask->parent;
@@ -396,11 +396,8 @@ static int aead_check_key(struct socket *sock) 
	if (crypto_aead_get_flags(tfm->aead) & CRYPTO_TFM_NEED_KEY)

		goto unlock;



	if (!pask->refcnt++)

		sock_hold(psk);



	ask->refcnt = 1;

	sock_put(psk);

	atomic_dec(&pask->nokey_refcnt);

	atomic_set(&ask->nokey_refcnt, 0);



	err = 0;

crypto/algif_hash.c

+3 −6
Original line number Diff line number Diff line
@@ -301,7 +301,7 @@ static int hash_check_key(struct socket *sock) 
	struct alg_sock *ask = alg_sk(sk);



	lock_sock(sk);

	if (ask->refcnt)

	if (!atomic_read(&ask->nokey_refcnt))

		goto unlock_child;



	psk = ask->parent;
@@ -313,11 +313,8 @@ static int hash_check_key(struct socket *sock) 
	if (crypto_ahash_get_flags(tfm) & CRYPTO_TFM_NEED_KEY)

		goto unlock;



	if (!pask->refcnt++)

		sock_hold(psk);



	ask->refcnt = 1;

	sock_put(psk);

	atomic_dec(&pask->nokey_refcnt);

	atomic_set(&ask->nokey_refcnt, 0);



	err = 0;

crypto/algif_skcipher.c

+3 −6
Original line number Diff line number Diff line
@@ -211,7 +211,7 @@ static int skcipher_check_key(struct socket *sock) 
	struct alg_sock *ask = alg_sk(sk);



	lock_sock(sk);

	if (ask->refcnt)

	if (!atomic_read(&ask->nokey_refcnt))

		goto unlock_child;



	psk = ask->parent;
@@ -223,11 +223,8 @@ static int skcipher_check_key(struct socket *sock) 
	if (crypto_skcipher_get_flags(tfm) & CRYPTO_TFM_NEED_KEY)

		goto unlock;



	if (!pask->refcnt++)

		sock_hold(psk);



	ask->refcnt = 1;

	sock_put(psk);

	atomic_dec(&pask->nokey_refcnt);

	atomic_set(&ask->nokey_refcnt, 0);



	err = 0;

include/crypto/if_alg.h

+2 −2
Original line number Diff line number Diff line
@@ -29,8 +29,8 @@ struct alg_sock { 


	struct sock *parent;



	unsigned int refcnt;

	unsigned int nokey_refcnt;

	atomic_t refcnt;

	atomic_t nokey_refcnt;



	const struct af_alg_type *type;

	void *private;

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