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Date:   Thu, 3 Sep 2020 20:57:01 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Wouter Verhelst <w@...r.be>
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

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

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 think that regardless of whether NBD expects only SOCK_STREAM sockets,
tipc_wait_for_rcvmsg() on a SOCK_DGRAM socket can't return is a bug.
David Miller already applied this patch and queued up for -stable.
Do we need to revert this patch?

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