[PATCH] nbd: Fix hung when signal interrupts nbd_start_device_ioctl()

[PATCH] nbd: Fix hung when signal interrupts nbd_start_device_ioctl()

[Shigeru Yoshida]

syzbot reported hung task [1].  The following program is a simplified
version of the reproducer:

int main(void)
{
	int sv[2], fd;

	if (socketpair(AF_UNIX, SOCK_STREAM, 0, sv) < 0)
		return 1;
	if ((fd = open("/dev/nbd0", 0)) < 0)
		return 1;
	if (ioctl(fd, NBD_SET_SIZE_BLOCKS, 0x81) < 0)
		return 1;
	if (ioctl(fd, NBD_SET_SOCK, sv[0]) < 0)
		return 1;
	if (ioctl(fd, NBD_DO_IT) < 0)
		return 1;
	return 0;
}

When signal interrupt nbd_start_device_ioctl() waiting the condition
atomic_read(&config->recv_threads) == 0, the task can hung because it
waits the completion of the inflight IOs.

This patch fixes the issue by clearing queue, not just shutdown, when
signal interrupt nbd_start_device_ioctl().

Link: https://syzkaller.appspot.com/bug?id=7d89a3ffacd2b83fdd39549bc4d8e0a89ef21239 [1]
Reported-by: syzbot+38e6c55d4969a14c1534@syzkaller.appspotmail.com
Signed-off-by: Shigeru Yoshida <syoshida@redhat.com>
---
 drivers/block/nbd.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 2a709daefbc4..2a2a1d996a57 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -1413,10 +1413,12 @@ static int nbd_start_device_ioctl(struct nbd_device *nbd)
 	mutex_unlock(&nbd->config_lock);
 	ret = wait_event_interruptible(config->recv_wq,
 					 atomic_read(&config->recv_threads) == 0);
-	if (ret)
+	if (ret) {
 		sock_shutdown(nbd);
-	flush_workqueue(nbd->recv_workq);
+		nbd_clear_que(nbd);
+	}
 
+	flush_workqueue(nbd->recv_workq);
 	mutex_lock(&nbd->config_lock);
 	nbd_bdev_reset(nbd);
 	/* user requested, ignore socket errors */
-- 
2.37.3

Re: [PATCH] nbd: Fix hung when signal interrupts nbd_start_device_ioctl()

[Josef Bacik]

On Thu, Sep 08, 2022 at 01:35:02AM +0900, Shigeru Yoshida wrote:
> syzbot reported hung task [1].  The following program is a simplified
> version of the reproducer:
> 
> int main(void)
> {
> 	int sv[2], fd;
> 
> 	if (socketpair(AF_UNIX, SOCK_STREAM, 0, sv) < 0)
> 		return 1;
> 	if ((fd = open("/dev/nbd0", 0)) < 0)
> 		return 1;
> 	if (ioctl(fd, NBD_SET_SIZE_BLOCKS, 0x81) < 0)
> 		return 1;
> 	if (ioctl(fd, NBD_SET_SOCK, sv[0]) < 0)
> 		return 1;
> 	if (ioctl(fd, NBD_DO_IT) < 0)
> 		return 1;
> 	return 0;
> }
> 
> When signal interrupt nbd_start_device_ioctl() waiting the condition
> atomic_read(&config->recv_threads) == 0, the task can hung because it
> waits the completion of the inflight IOs.
> 
> This patch fixes the issue by clearing queue, not just shutdown, when
> signal interrupt nbd_start_device_ioctl().
> 
> Link: https://syzkaller.appspot.com/bug?id=7d89a3ffacd2b83fdd39549bc4d8e0a89ef21239 [1]
> Reported-by: syzbot+38e6c55d4969a14c1534@syzkaller.appspotmail.com
> Signed-off-by: Shigeru Yoshida <syoshida@redhat.com>

Reviewed-by: Josef Bacik <josef@toxicpanda.com>

Thanks,

Josef

Re: [PATCH] nbd: Fix hung when signal interrupts nbd_start_device_ioctl()

[Jens Axboe]

On Thu, 8 Sep 2022 01:35:02 +0900, Shigeru Yoshida wrote:
> syzbot reported hung task [1].  The following program is a simplified
> version of the reproducer:
> 
> int main(void)
> {
> 	int sv[2], fd;
> 
> [...]

Applied, thanks!

[1/1] nbd: Fix hung when signal interrupts nbd_start_device_ioctl()
      commit: 1de7c3cf48fc41cd95adb12bd1ea9033a917798a

Best regards,
-- 
Jens Axboe