diff options
authorEric Dumazet <>2021-06-16 07:47:15 -0700
committerDavid S. Miller <>2021-06-16 12:51:55 -0700
commita494bd642d9120648b06bb7d28ce6d05f55a7819 (patch)
parent0fd158b89b50b3a31c97a639ff496e1c59686e97 (diff)
net/af_unix: fix a data-race in unix_dgram_sendmsg / unix_release_sock
While unix_may_send(sk, osk) is called while osk is locked, it appears unix_release_sock() can overwrite unix_peer() after this lock has been released, making KCSAN unhappy. Changing unix_release_sock() to access/change unix_peer() before lock is released should fix this issue. BUG: KCSAN: data-race in unix_dgram_sendmsg / unix_release_sock write to 0xffff88810465a338 of 8 bytes by task 20852 on cpu 1: unix_release_sock+0x4ed/0x6e0 net/unix/af_unix.c:558 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:175 [inline] exit_to_user_mode_prepare+0x156/0x190 kernel/entry/common.c:209 __syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline] syscall_exit_to_user_mode+0x20/0x40 kernel/entry/common.c:302 do_syscall_64+0x56/0x90 arch/x86/entry/common.c:57 entry_SYSCALL_64_after_hwframe+0x44/0xae read to 0xffff88810465a338 of 8 bytes by task 20888 on cpu 0: unix_may_send net/unix/af_unix.c:189 [inline] unix_dgram_sendmsg+0x923/0x1610 net/unix/af_unix.c:1712 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: 0xffff888167905400 -> 0x0000000000000000 Reported by Kernel Concurrency Sanitizer on: CPU: 0 PID: 20888 Comm: syz-executor.0 Not tainted 5.13.0-rc5-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: Eric Dumazet <> Reported-by: syzbot <> Signed-off-by: David S. Miller <>
1 files changed, 4 insertions, 3 deletions
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 5a31307ceb76..5d1192ceb139 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -535,12 +535,14 @@ static void unix_release_sock(struct sock *sk, int embrion)
u->path.mnt = NULL;
state = sk->sk_state;
sk->sk_state = TCP_CLOSE;
+ skpair = unix_peer(sk);
+ unix_peer(sk) = NULL;
- skpair = unix_peer(sk);
if (skpair != NULL) {
if (sk->sk_type == SOCK_STREAM || sk->sk_type == SOCK_SEQPACKET) {
@@ -555,7 +557,6 @@ static void unix_release_sock(struct sock *sk, int embrion)
unix_dgram_peer_wake_disconnect(sk, skpair);
sock_put(skpair); /* It may now die */
- unix_peer(sk) = NULL;
/* Try to flush out this socket. Throw out buffers at least */