So.

On Wed, Sep 02, 2020 at 08:09:54PM +0900, Tetsuo Handa wrote:
> syzbot is reporting hung task at nbd_ioctl() [1], for there are two
> problems regarding TIPC's connectionless socket's shutdown() operation.
> I found C reproducer for this problem (shown below) from "no output from
> test machine (2)" report.
> 
> ----------
> 
> int main(int argc, char *argv[])
> {
>         const int fd = open("/dev/nbd0", 3);
>         ioctl(fd, NBD_SET_SOCK, socket(PF_TIPC, SOCK_DGRAM, 0));

NBD expects a stream socket, not a datagram one.

>         ioctl(fd, NBD_DO_IT, 0);

This is supposed to sit and wait until someone disconnects the device
again (which you probably cna't do with datagram sockets). Changing that
changes a userspace API.

-- 
To the thief who stole my anti-depressants: I hope you're happy

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