nbd: Fix hung when signal interrupts nbd_start_device_ioctl()

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: nbd: Fix hung when signal interrupts nbd_start_device_ioctl() 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().

References

• https://git.kernel.org/stable/c/3ba3846cb3e2fb3c6fbf79e998472821b298419e
• https://git.kernel.org/stable/c/c7b4641bd2395c2f3cd3b0a0cbf292ed9d489398
• https://git.kernel.org/stable/c/3575949513ea3b387b30dac1e69468a923c86caf
• https://git.kernel.org/stable/c/b2700f98b3f4dd19fb4315b70581e5caff89eb49
• https://git.kernel.org/stable/c/c0d73be0af8c1310713bc39a8d7a22e35084e14f
• https://git.kernel.org/stable/c/62006a72b05e0d38727eef5188700f2488be5e89
• https://git.kernel.org/stable/c/35fb7d4a53d9e36d1b91161ea9870d9c6d57dccf
• https://git.kernel.org/stable/c/1de7c3cf48fc41cd95adb12bd1ea9033a917798a