CVE-2022-50314: nbd: Fix hung when signal interrupts nbd_start_device_ioctl()

In the Linux kernel, the following vulnerability has been resolved:

nbd: Fix hung when signal interrupts nbdstartdeviceioctl()

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

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

if (socketpair(AFUNIX, SOCKSTREAM, 0, sv) < 0) return 1; if ((fd = open("/dev/nbd0", 0)) < 0) return 1; if (ioctl(fd, NBDSETSIZEBLOCKS, 0x81) < 0) return 1; if (ioctl(fd, NBDSETSOCK, sv[0]) < 0) return 1; if (ioctl(fd, NBDDOIT) < 0) return 1; return 0; }

When signal interrupt nbdstartdeviceioctl() waiting the condition atomicread(&config->recvthreads) == 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 nbdstartdeviceioctl().