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authorQian Cai <cai@lca.pw>2020-02-04 13:40:29 -0500
committerDavid S. Miller <davem@davemloft.net>2020-02-06 13:59:10 +0100
commit86b18aaa2b5b5bb48e609cd591b3d2d0fdbe0442 (patch)
tree39d9ae29d9d944e6a14ed4ddc323b145f1b6b9c0 /net
parentc35947b8ff8acca33134ee39c31708233765c31a (diff)
skbuff: fix a data race in skb_queue_len()
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>
Diffstat (limited to 'net')
-rw-r--r--net/unix/af_unix.c11
1 files changed, 9 insertions, 2 deletions
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 321af97c7bbe..62c12cb5763e 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -189,11 +189,17 @@ static inline int unix_may_send(struct sock *sk, struct sock *osk)
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;
@@ -1758,7 +1764,8 @@ restart_locked:
* - 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);