diff options
authorEric Dumazet <>2021-06-10 07:44:11 -0700
committerDavid S. Miller <>2021-06-10 14:12:54 -0700
commitb71eaed8c04f72a919a9c44e83e4ee254e69e7f3 (patch)
parentf13ef10059ccf5f4ed201cd050176df62ec25bb8 (diff)
inet: annotate date races around sk->sk_txhash
UDP sendmsg() path can be lockless, it is possible for another thread to re-connect an change sk->sk_txhash under us. There is no serious impact, but we can use READ_ONCE()/WRITE_ONCE() pair to document the race. BUG: KCSAN: data-race in __ip4_datagram_connect / skb_set_owner_w write to 0xffff88813397920c of 4 bytes by task 30997 on cpu 1: sk_set_txhash include/net/sock.h:1937 [inline] __ip4_datagram_connect+0x69e/0x710 net/ipv4/datagram.c:75 __ip6_datagram_connect+0x551/0x840 net/ipv6/datagram.c:189 ip6_datagram_connect+0x2a/0x40 net/ipv6/datagram.c:272 inet_dgram_connect+0xfd/0x180 net/ipv4/af_inet.c:580 __sys_connect_file net/socket.c:1837 [inline] __sys_connect+0x245/0x280 net/socket.c:1854 __do_sys_connect net/socket.c:1864 [inline] __se_sys_connect net/socket.c:1861 [inline] __x64_sys_connect+0x3d/0x50 net/socket.c:1861 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47 entry_SYSCALL_64_after_hwframe+0x44/0xae read to 0xffff88813397920c of 4 bytes by task 31039 on cpu 0: skb_set_hash_from_sk include/net/sock.h:2211 [inline] skb_set_owner_w+0x118/0x220 net/core/sock.c:2101 sock_alloc_send_pskb+0x452/0x4e0 net/core/sock.c:2359 sock_alloc_send_skb+0x2d/0x40 net/core/sock.c:2373 __ip6_append_data+0x1743/0x21a0 net/ipv6/ip6_output.c:1621 ip6_make_skb+0x258/0x420 net/ipv6/ip6_output.c:1983 udpv6_sendmsg+0x160a/0x16b0 net/ipv6/udp.c:1527 inet6_sendmsg+0x5f/0x80 net/ipv6/af_inet6.c:642 sock_sendmsg_nosec net/socket.c:654 [inline] sock_sendmsg net/socket.c:674 [inline] ____sys_sendmsg+0x360/0x4d0 net/socket.c:2350 ___sys_sendmsg net/socket.c:2404 [inline] __sys_sendmmsg+0x315/0x4b0 net/socket.c:2490 __do_sys_sendmmsg net/socket.c:2519 [inline] __se_sys_sendmmsg net/socket.c:2516 [inline] __x64_sys_sendmmsg+0x53/0x60 net/socket.c:2516 do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47 entry_SYSCALL_64_after_hwframe+0x44/0xae value changed: 0xbca3c43d -> 0xfdb309e0 Reported by Kernel Concurrency Sanitizer on: CPU: 0 PID: 31039 Comm: syz-executor.2 Not tainted 5.13.0-rc3-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Signed-off-by: Eric Dumazet <> Reported-by: syzbot <> Signed-off-by: David S. Miller <>
1 files changed, 7 insertions, 3 deletions
diff --git a/include/net/sock.h b/include/net/sock.h
index 2fc513aa114c..7a7058f4f265 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1934,7 +1934,8 @@ static inline u32 net_tx_rndhash(void)
static inline void sk_set_txhash(struct sock *sk)
- sk->sk_txhash = net_tx_rndhash();
+ /* This pairs with READ_ONCE() in skb_set_hash_from_sk() */
+ WRITE_ONCE(sk->sk_txhash, net_tx_rndhash());
static inline bool sk_rethink_txhash(struct sock *sk)
@@ -2206,9 +2207,12 @@ static inline void sock_poll_wait(struct file *filp, struct socket *sock,
static inline void skb_set_hash_from_sk(struct sk_buff *skb, struct sock *sk)
- if (sk->sk_txhash) {
+ /* This pairs with WRITE_ONCE() in sk_set_txhash() */
+ u32 txhash = READ_ONCE(sk->sk_txhash);
+ if (txhash) {
skb->l4_hash = 1;
- skb->hash = sk->sk_txhash;
+ skb->hash = txhash;