ACK: [D][PATCH] crypto: af_alg - fix use-after-free in af_alg_accept() due to bh_lock_sock()

Stefan Bader stefan.bader at canonical.com
Wed Jul 1 14:07:40 UTC 2020


On 01.07.20 01:10, Mauricio Faria de Oliveira wrote:
> From: Herbert Xu <herbert at gondor.apana.org.au>
> 
> BugLink: https://bugs.launchpad.net/bugs/1884766
> 
> 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: Brian Moyles <bmoyles at netflix.com>
> Reported-by: Mauricio Faria de Oliveira <mfo at canonical.com>
> Fixes: 37f96694cf73 ("crypto: af_alg - Use bh_lock_sock in...")
> Cc: <stable at vger.kernel.org>
> Signed-off-by: Herbert Xu <herbert at gondor.apana.org.au>
> (backported from commit 34c86f4c4a7be3b3e35aa48bd18299d4c756064d)
> [mfo: backport: refresh context lines in af_alg.c hunk 4]
> Signed-off-by: Mauricio Faria de Oliveira <mfo at canonical.com>
Acked-by: Stefan Bader <stefan.bader at canonical.com>
> ---
>  crypto/af_alg.c         | 26 +++++++++++---------------
>  crypto/algif_aead.c     |  9 +++------
>  crypto/algif_hash.c     |  9 +++------
>  crypto/algif_skcipher.c |  9 +++------
>  include/crypto/if_alg.h |  4 ++--
>  5 files changed, 22 insertions(+), 35 deletions(-)
> 
> diff --git a/crypto/af_alg.c b/crypto/af_alg.c
> index 4fc8e6a7abb2..272879d7b0d1 100644
> --- a/crypto/af_alg.c
> +++ b/crypto/af_alg.c
> @@ -133,21 +133,15 @@ 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);
> @@ -192,7 +186,7 @@ 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);
> @@ -241,7 +235,7 @@ 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;
> @@ -308,12 +302,14 @@ int af_alg_accept(struct sock *sk, struct socket *newsock, bool kern)
>  
>  	sk2->sk_family = PF_ALG;
>  
> -	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;
> diff --git a/crypto/algif_aead.c b/crypto/algif_aead.c
> index eb100a04ce9f..e643d268c7ba 100644
> --- a/crypto/algif_aead.c
> +++ b/crypto/algif_aead.c
> @@ -388,7 +388,7 @@ 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;
> @@ -400,11 +400,8 @@ 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;
>  
> diff --git a/crypto/algif_hash.c b/crypto/algif_hash.c
> index d0cde541beb6..73abe6a33f3a 100644
> --- a/crypto/algif_hash.c
> +++ b/crypto/algif_hash.c
> @@ -306,7 +306,7 @@ 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;
> @@ -318,11 +318,8 @@ 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;
>  
> diff --git a/crypto/algif_skcipher.c b/crypto/algif_skcipher.c
> index cfdaab2b7d76..75444b8beed9 100644
> --- a/crypto/algif_skcipher.c
> +++ b/crypto/algif_skcipher.c
> @@ -219,7 +219,7 @@ 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;
> @@ -231,11 +231,8 @@ 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;
>  
> diff --git a/include/crypto/if_alg.h b/include/crypto/if_alg.h
> index 482461d8931d..11f107df78dc 100644
> --- a/include/crypto/if_alg.h
> +++ b/include/crypto/if_alg.h
> @@ -34,8 +34,8 @@ 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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