[PATCH 4.19 09/17] net: annotate data race around sk_ll_usec

Greg Kroah-Hartman
2021-07-29T13:57:08Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 0dbffbb5335a1e3aa6855e4ee317e25e669dd302 ]

sk_ll_usec is read locklessly from sk_can_busy_loop()
while another thread can change its value in sock_setsockopt()

This is correct but needs annotations.

BUG: KCSAN: data-race in __skb_try_recv_datagram / sock_setsockopt

write to 0xffff88814eb5f904 of 4 bytes by task 14011 on cpu 0:
sock_setsockopt+0x1287/0x2090 net/core/sock.c:1175
__sys_setsockopt+0x14f/0x200 net/socket.c:2100
__do_sys_setsockopt net/socket.c:2115 [inline]
__se_sys_setsockopt net/socket.c:2112 [inline]
__x64_sys_setsockopt+0x62/0x70 net/socket.c:2112
do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff88814eb5f904 of 4 bytes by task 14001 on cpu 1:
sk_can_busy_loop include/net/busy_poll.h:41 [inline]
__skb_try_recv_datagram+0x14f/0x320 net/core/datagram.c:273
unix_dgram_recvmsg+0x14c/0x870 net/unix/af_unix.c:2101
unix_seqpacket_recvmsg+0x5a/0x70 net/unix/af_unix.c:2067
____sys_recvmsg+0x15d/0x310 include/linux/uio.h:244
___sys_recvmsg net/socket.c:2598 [inline]
do_recvmmsg+0x35c/0x9f0 net/socket.c:2692
__sys_recvmmsg net/socket.c:2771 [inline]
__do_sys_recvmmsg net/socket.c:2794 [inline]
__se_sys_recvmmsg net/socket.c:2787 [inline]
__x64_sys_recvmmsg+0xcf/0x150 net/socket.c:2787
do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x00000000 -> 0x00000101

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 14001 Comm: syz-executor.3 Not tainted 5.13.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/net/busy_poll.h | 2 +-
net/core/sock.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/net/busy_poll.h b/include/net/busy_poll.h
index cf8f792743ec..c76a5e9894da 100644
--- a/include/net/busy_poll.h
+++ b/include/net/busy_poll.h
@@ -48,7 +48,7 @@ static inline bool net_busy_loop_on(void)

static inline bool sk_can_busy_loop(const struct sock *sk)
{
- return sk->sk_ll_usec && !signal_pending(current);
+ return READ_ONCE(sk->sk_ll_usec) && !signal_pending(current);
}

bool sk_busy_loop_end(void *p, unsigned long start_time);
diff --git a/net/core/sock.c b/net/core/sock.c
index e6cbe137cb6f..956af38aa0d6 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -989,7 +989,7 @@ set_rcvbuf:
if (val < 0)
ret = -EINVAL;
else
- sk->sk_ll_usec = val;
+ WRITE_ONCE(sk->sk_ll_usec, val);
}
break;
#endif
--
2.30.2