linux-kernel - Re: [V9fs-developer] [PATCH] 9p: fix NULL pointer dereferences

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Message-ID: <CAM104AUnMsQvH7VPMhZcGK+3UTiXT3MiahwfkGeN7Sj1CpQfCQ@mail.gmail.com>
Date:   Thu, 26 Jul 2018 22:48:50 +0800
From:   sqweek <sqweek@...il.com>
To:     Dominique Martinet <asmadeus@...ewreck.org>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller <syzkaller@...glegroups.com>,
        V9FS Developers <v9fs-developer@...ts.sourceforge.net>,
        Tomas Bortoli <tomasbortoli@...il.com>,
        David Miller <davem@...emloft.net>
Subject: Re: [V9fs-developer] [PATCH] 9p: fix NULL pointer dereferences

On 26 July 2018 at 17:48, Dominique Martinet <asmadeus@...ewreck.org> wrote:

> Dmitry Vyukov wrote on Thu, Jul 26, 2018:
> > > Let's refuse that at much higher level, like v9fs_mount() in
> > > fs/9p/vfs_super.c
> > >
> > > I can't think of any valid reason for dev_name to be NULL, it's the
> > > target IP or virtio handle.
> >
> > But I think trans=fd allows NULL addr today, no?
>
> Ah, right, I read the patch too fast and read unix_create as fd_create,
> I never realized there was a unix_create variant...
>
> fd legitimately doesn't need a name, you are correct.
>
> I'm really curious if anyone ever uses the unix/fd variants for "real"
> stuff though!

I definitely used the unix variant for mounting plan9port servers (which
all listen for 9p requests via unix sockets).

A long time ago I also experimented with mounting p9p servers from remote
machines and I think I might have combined socat with -o trans=fd at one
point. But I gave up on it in the end because having a process blocked in
read() was preventing my laptop from going to sleep for the duration. And
since I was trying to read /event type files the Tread could block for
quite some time if no events were posted.

I believe 9pfuse had the same issue, so the problem be deeper than v9fs.
But anyway I'm on quite a tangent already so I'll stop distracting you all
from the work at hand. It's been nice to see 9p still kicking recently! :)

> (not meaning syzbot isn't real, but I have yet to see
> anything take advantage of this, even if I could imagine some fun
> applications by piping the wmii libixp server socket..
>

Wait woahhhhh, there's another wmii user left? I thought I was the last one!
-sqweek

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