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

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Message-ID: <20200903113141.GB8553@pc181009.grep.be>
Date:   Thu, 3 Sep 2020 13:31:41 +0200
From:   Wouter Verhelst <w@...r.be>
To:     Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:     syzbot <syzbot+e36f41d207137b5d12f7@...kaller.appspotmail.com>,
        Jon Maloy <jmaloy@...hat.com>,
        Ying Xue <ying.xue@...driver.com>,
        syzkaller-bugs@...glegroups.com,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        tipc-discussion@...ts.sourceforge.net
Subject: Re: [PATCH] tipc: fix shutdown() of connectionless socket

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.

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