From 34c86f4c4a7be3b3e35aa48bd18299d4c756064d Mon Sep 17 00:00:00 2001 From: Herbert Xu Date: Mon, 8 Jun 2020 16:48:43 +1000 Subject: 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 Reported-by: Mauricio Faria de Oliveira Fixes: 37f96694cf73 ("crypto: af_alg - Use bh_lock_sock in...") Cc: Signed-off-by: Herbert Xu --- crypto/af_alg.c | 26 +++++++++++--------------- 1 file changed, 11 insertions(+), 15 deletions(-) (limited to 'crypto/af_alg.c') diff --git a/crypto/af_alg.c b/crypto/af_alg.c index b1cd3535c525..28fc323e3fe3 100644 --- a/crypto/af_alg.c +++ b/crypto/af_alg.c @@ -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; -- cgit v1.2.3