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

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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
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9
crypto/algif_hash.c
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@@ -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;