skbuff: fix a data race in skb_queue_len()
[ Upstream commit 86b18aaa2b5b5bb48e609cd591b3d2d0fdbe0442 ]
sk_buff.qlen can be accessed concurrently as noticed by KCSAN,
BUG: KCSAN: data-race in __skb_try_recv_from_queue / unix_dgram_sendmsg
read to 0xffff8a1b1d8a81c0 of 4 bytes by task 5371 on cpu 96:
unix_dgram_sendmsg+0x9a9/0xb70 include/linux/skbuff.h:1821
net/unix/af_unix.c:1761
____sys_sendmsg+0x33e/0x370
___sys_sendmsg+0xa6/0xf0
__sys_sendmsg+0x69/0xf0
__x64_sys_sendmsg+0x51/0x70
do_syscall_64+0x91/0xb47
entry_SYSCALL_64_after_hwframe+0x49/0xbe
write to 0xffff8a1b1d8a81c0 of 4 bytes by task 1 on cpu 99:
__skb_try_recv_from_queue+0x327/0x410 include/linux/skbuff.h:2029
__skb_try_recv_datagram+0xbe/0x220
unix_dgram_recvmsg+0xee/0x850
____sys_recvmsg+0x1fb/0x210
___sys_recvmsg+0xa2/0xf0
__sys_recvmsg+0x66/0xf0
__x64_sys_recvmsg+0x51/0x70
do_syscall_64+0x91/0xb47
entry_SYSCALL_64_after_hwframe+0x49/0xbe
Since only the read is operating as lockless, it could introduce a logic
bug in unix_recvq_full() due to the load tearing. Fix it by adding
a lockless variant of skb_queue_len() and unix_recvq_full() where
READ_ONCE() is on the read while WRITE_ONCE() is on the write similar to
the commit d7d16a89350a ("net: add skb_queue_empty_lockless()").
Signed-off-by: Qian Cai <cai@lca.pw>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
(cherry picked from commit ce5d34a31676bb33b578577d64dcf4111a03eceb)
Change-Id: Ia72d1e605cb54a5d1f8ecf359b590120c3607cc4
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index e7012a5..3aaf209 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -191,11 +191,17 @@
return unix_peer(osk) == NULL || unix_our_peer(sk, osk);
}
-static inline int unix_recvq_full(struct sock const *sk)
+static inline int unix_recvq_full(const struct sock *sk)
{
return skb_queue_len(&sk->sk_receive_queue) > sk->sk_max_ack_backlog;
}
+static inline int unix_recvq_full_lockless(const struct sock *sk)
+{
+ return skb_queue_len_lockless(&sk->sk_receive_queue) >
+ READ_ONCE(sk->sk_max_ack_backlog);
+}
+
struct sock *unix_peer_get(struct sock *s)
{
struct sock *peer;
@@ -1793,7 +1799,8 @@
* - unix_peer(sk) == sk by time of get but disconnected before lock
*/
if (other != sk &&
- unlikely(unix_peer(other) != sk && unix_recvq_full(other))) {
+ unlikely(unix_peer(other) != sk &&
+ unix_recvq_full_lockless(other))) {
if (timeo) {
timeo = unix_wait_for_peer(other, timeo);