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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: Brian Moyles <bmoyles@netflix.com>
Reported-by: Mauricio Faria de Oliveira <mfo@canonical.com>
Fixes: 37f96694cf ("crypto: af_alg - Use bh_lock_sock in...")
Cc: <stable@vger.kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
This commit is contained in:
Herbert Xu 2020-06-08 16:48:43 +10:00
parent 819966c06b
commit 34c86f4c4a
5 changed files with 22 additions and 35 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

26
crypto/af_alg.c
View File

@ -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;

9
crypto/algif_aead.c
View File

@ -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;

9
crypto/algif_hash.c
View File

@ -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;

9
crypto/algif_skcipher.c
View File

@ -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;

4
include/crypto/if_alg.h
View File

@ -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;