[PATCH AUTOSEL 5.12 18/39] net: annotate data race in sock_error()

Sasha Levin
2021-06-21T17:53:30Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit f13ef10059ccf5f4ed201cd050176df62ec25bb8 ]

sock_error() is known to be racy. The code avoids
an atomic operation is sk_err is zero, and this field
could be changed under us, this is fine.

Sysbot reported:

BUG: KCSAN: data-race in sock_alloc_send_pskb / unix_release_sock

write to 0xffff888131855630 of 4 bytes by task 9365 on cpu 1:
unix_release_sock+0x2e9/0x6e0 net/unix/af_unix.c:550
unix_release+0x2f/0x50 net/unix/af_unix.c:859
__sock_release net/socket.c:599 [inline]
sock_close+0x6c/0x150 net/socket.c:1258
__fput+0x25b/0x4e0 fs/file_table.c:280
____fput+0x11/0x20 fs/file_table.c:313
task_work_run+0xae/0x130 kernel/task_work.c:164
tracehook_notify_resume include/linux/tracehook.h:189 [inline]
exit_to_user_mode_loop kernel/entry/common.c:174 [inline]
exit_to_user_mode_prepare+0x156/0x190 kernel/entry/common.c:208
__syscall_exit_to_user_mode_work kernel/entry/common.c:290 [inline]
syscall_exit_to_user_mode+0x20/0x40 kernel/entry/common.c:301
do_syscall_64+0x56/0x90 arch/x86/entry/common.c:57
entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff888131855630 of 4 bytes by task 9385 on cpu 0:
sock_error include/net/sock.h:2269 [inline]
sock_alloc_send_pskb+0xe4/0x4e0 net/core/sock.c:2336
unix_dgram_sendmsg+0x478/0x1610 net/unix/af_unix.c:1671
unix_seqpacket_sendmsg+0xc2/0x100 net/unix/af_unix.c:2055
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_sock+0x25/0x30 net/socket.c:2416
io_sendmsg fs/io_uring.c:4367 [inline]
io_issue_sqe+0x231a/0x6750 fs/io_uring.c:6135
__io_queue_sqe+0xe9/0x360 fs/io_uring.c:6414
__io_req_task_submit fs/io_uring.c:2039 [inline]
io_async_task_func+0x312/0x590 fs/io_uring.c:5074
__tctx_task_work fs/io_uring.c:1910 [inline]
tctx_task_work+0x1d4/0x3d0 fs/io_uring.c:1924
task_work_run+0xae/0x130 kernel/task_work.c:164
tracehook_notify_signal include/linux/tracehook.h:212 [inline]
handle_signal_work kernel/entry/common.c:145 [inline]
exit_to_user_mode_loop kernel/entry/common.c:171 [inline]
exit_to_user_mode_prepare+0xf8/0x190 kernel/entry/common.c:208
__syscall_exit_to_user_mode_work kernel/entry/common.c:290 [inline]
syscall_exit_to_user_mode+0x20/0x40 kernel/entry/common.c:301
do_syscall_64+0x56/0x90 arch/x86/entry/common.c:57
entry_SYSCALL_64_after_hwframe+0x44/0xae

value changed: 0x00000000 -> 0x00000068

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 9385 Comm: syz-executor.3 Not tainted 5.13.0-rc4-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/sock.h | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/include/net/sock.h b/include/net/sock.h
index 62e3811e95a7..b98c80a7c7ae 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -2260,8 +2260,13 @@ struct sk_buff *sock_dequeue_err_skb(struct sock *sk);
static inline int sock_error(struct sock *sk)
{
int err;
- if (likely(!sk->sk_err))
+
+ /* Avoid an atomic operation for the common case.
+ * This is racy since another cpu/thread can change sk_err under us.
+ */
+ if (likely(data_race(!sk->sk_err)))
return 0;
+
err = xchg(&sk->sk_err, 0);
return -err;
}
--
2.30.2