[PATCH 4.19 6/8] tipc: fix shutdown() of connectionless socket

From: Greg Kroah-Hartman
Date: Fri Sep 11 2020 - 10:26:18 EST

From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>

[ Upstream commit 2a63866c8b51a3f72cea388dfac259d0e14c4ba6 ]

syzbot is reporting hung task at nbd_ioctl() [1], for there are two
problems regarding TIPC's connectionless socket's shutdown() operation.

#include <fcntl.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <linux/nbd.h>
#include <unistd.h>

int main(int argc, char *argv[])
const int fd = open("/dev/nbd0", 3);
ioctl(fd, NBD_SET_SOCK, socket(PF_TIPC, SOCK_DGRAM, 0));
ioctl(fd, NBD_DO_IT, 0); /* To be interrupted by SIGALRM. */
return 0;

One problem is that wait_for_completion() from flush_workqueue() from
nbd_start_device_ioctl() from nbd_ioctl() cannot be completed when
nbd_start_device_ioctl() received a signal at wait_event_interruptible(),
for tipc_shutdown() from kernel_sock_shutdown(SHUT_RDWR) from
nbd_mark_nsock_dead() from sock_shutdown() from nbd_start_device_ioctl()
is failing to wake up a WQ thread sleeping at wait_woken() from
tipc_wait_for_rcvmsg() from sock_recvmsg() from sock_xmit() from
nbd_read_stat() from recv_work() scheduled by nbd_start_device() from
nbd_start_device_ioctl(). Fix this problem by always invoking
sk->sk_state_change() (like inet_shutdown() does) when tipc_shutdown() is

The other problem is that tipc_wait_for_rcvmsg() cannot return when
tipc_shutdown() is called, for tipc_shutdown() sets sk->sk_shutdown to
SEND_SHUTDOWN (despite "how" is SHUT_RDWR) while tipc_wait_for_rcvmsg()
needs sk->sk_shutdown set to RCV_SHUTDOWN or SHUTDOWN_MASK. Fix this
problem by setting sk->sk_shutdown to SHUTDOWN_MASK (like inet_shutdown()
does) when the socket is connectionless.

[1] https://syzkaller.appspot.com/bug?id=3fe51d307c1f0a845485cf1798aa059d12bf18b2

Reported-by: syzbot <syzbot+e36f41d207137b5d12f7@xxxxxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
net/tipc/socket.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)

--- a/net/tipc/socket.c
+++ b/net/tipc/socket.c
@@ -2565,18 +2565,21 @@ static int tipc_shutdown(struct socket *

__tipc_shutdown(sock, TIPC_CONN_SHUTDOWN);
- sk->sk_shutdown = SEND_SHUTDOWN;
+ if (tipc_sk_type_connectionless(sk))
+ sk->sk_shutdown = SHUTDOWN_MASK;
+ else
+ sk->sk_shutdown = SEND_SHUTDOWN;

if (sk->sk_state == TIPC_DISCONNECTING) {
/* Discard any unreceived messages */

- /* Wake up anyone sleeping in poll */
- sk->sk_state_change(sk);
res = 0;
} else {
res = -ENOTCONN;
+ /* Wake up anyone sleeping in poll. */
+ sk->sk_state_change(sk);

return res;