Re: [PATCH] tipc: fix shutdown() of connectionless socket

On Thu, Sep 03, 2020 at 08:57:01PM +0900, Tetsuo Handa wrote:

On 2020/09/03 20:31, Wouter Verhelst wrote:

quoted

So.

On Wed, Sep 02, 2020 at 08:09:54PM +0900, Tetsuo Handa wrote:

quoted

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.

quoted

        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.

Excuse me, but other datagram sockets (e.g. socket(PF_INET, SOCK_DGRAM, 0)) does not
hit this problem. What do you want to do? Add a "whether the file descriptor passed
to ioctl(NBD_SET_SOCK) is a SOCK_STREAM socket" test to the NBD side?

I missed originally that you were checking whether the passed socket is
in fact a SOCK_DGRAM socket, and limiting the changes to that. That's
fine, because NBD doesn't deal with SOCK_DGRAM sockets anyway (i.e.,
passing a SOCK_DGRAM socket to the NBD device is undefined behavior). If
the behavior also changes for SOCK_STREAM sockets then that would be a
problem that would need to be reverted, but otherwise it's fine.

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