From: Kuniyuki Iwashima kuniyu@amazon.co.jp
[ Upstream commit e82025c623e2bf04d162bafceb66a59115814479 ]
Out-of-band data automatically places a "mark" showing wherein the sequence the out-of-band data would have been. If the out-of-band data implies cancelling everything sent so far, the "mark" is helpful to flush them. When the socket's read pointer reaches the "mark", the ioctl() below sets a non zero value to the arg `atmark`:
The out-of-band data is queued in sk->sk_receive_queue as well as ordinary data and also saved in unix_sk(sk)->oob_skb. It can be used to test if the head of the receive queue is the out-of-band data meaning the socket is at the "mark".
While testing that, unix_ioctl() reads unix_sk(sk)->oob_skb locklessly. Thus, all accesses to oob_skb need some basic protection to avoid load/store tearing which KCSAN detects when these are called concurrently:
- ioctl(fd_a, SIOCATMARK, &atmark, sizeof(atmark)) - send(fd_b_connected_to_a, buf, sizeof(buf), MSG_OOB)
BUG: KCSAN: data-race in unix_ioctl / unix_stream_sendmsg
write to 0xffff888003d9cff0 of 8 bytes by task 175 on cpu 1: unix_stream_sendmsg (net/unix/af_unix.c:2087 net/unix/af_unix.c:2191) sock_sendmsg (net/socket.c:705 net/socket.c:725) __sys_sendto (net/socket.c:2040) __x64_sys_sendto (net/socket.c:2048) do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:113)
read to 0xffff888003d9cff0 of 8 bytes by task 176 on cpu 0: unix_ioctl (net/unix/af_unix.c:3101 (discriminator 1)) sock_do_ioctl (net/socket.c:1128) sock_ioctl (net/socket.c:1242) __x64_sys_ioctl (fs/ioctl.c:52 fs/ioctl.c:874 fs/ioctl.c:860 fs/ioctl.c:860) do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:113)
value changed: 0xffff888003da0c00 -> 0xffff888003da0d00
Reported by Kernel Concurrency Sanitizer on: CPU: 0 PID: 176 Comm: unix_race_oob_i Not tainted 5.17.0-rc5-59529-g83dc4c2af682 #12 Hardware name: Red Hat KVM, BIOS 1.11.0-2.amzn2 04/01/2014
Fixes: 314001f0bf92 ("af_unix: Add OOB support") Signed-off-by: Kuniyuki Iwashima kuniyu@amazon.co.jp Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin sashal@kernel.org --- net/unix/af_unix.c | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-)
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c index b0bfc78e421c..826ac391a7a4 100644 --- a/net/unix/af_unix.c +++ b/net/unix/af_unix.c @@ -1996,7 +1996,7 @@ static int queue_oob(struct socket *sock, struct msghdr *msg, struct sock *other if (ousk->oob_skb) consume_skb(ousk->oob_skb);
- ousk->oob_skb = skb; + WRITE_ONCE(ousk->oob_skb, skb);
scm_stat_add(other, skb); skb_queue_tail(&other->sk_receive_queue, skb); @@ -2514,9 +2514,8 @@ static int unix_stream_recv_urg(struct unix_stream_read_state *state)
oob_skb = u->oob_skb;
- if (!(state->flags & MSG_PEEK)) { - u->oob_skb = NULL; - } + if (!(state->flags & MSG_PEEK)) + WRITE_ONCE(u->oob_skb, NULL);
unix_state_unlock(sk);
@@ -2551,7 +2550,7 @@ static struct sk_buff *manage_oob(struct sk_buff *skb, struct sock *sk, skb = NULL; } else if (sock_flag(sk, SOCK_URGINLINE)) { if (!(flags & MSG_PEEK)) { - u->oob_skb = NULL; + WRITE_ONCE(u->oob_skb, NULL); consume_skb(skb); } } else if (!(flags & MSG_PEEK)) { @@ -3006,11 +3005,10 @@ static int unix_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg) case SIOCATMARK: { struct sk_buff *skb; - struct unix_sock *u = unix_sk(sk); int answ = 0;
skb = skb_peek(&sk->sk_receive_queue); - if (skb && skb == u->oob_skb) + if (skb && skb == READ_ONCE(unix_sk(sk)->oob_skb)) answ = 1; err = put_user(answ, (int __user *)arg); }