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

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Message-ID: <baa7368f-e149-ef3d-cf10-4fcd16dce0e6@gmail.com>
Date:   Thu, 26 Jul 2018 16:32:15 +0200
From:   Tomas Bortoli <tomasbortoli@...il.com>
To:     Dominique Martinet <asmadeus@...ewreck.org>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        David Miller <davem@...emloft.net>,
        v9fs-developer@...ts.sourceforge.net,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: [PATCH] 9p: fix NULL pointer dereferences

On 07/26/2018 04:21 PM, Dominique Martinet wrote:
> Tomas Bortoli wrote on Thu, Jul 26, 2018:
>>> But I think trans=fd allows NULL addr today, no?
>>
>> How ?
> 
> Just using the mount syscall with a NULL dev_name? I haven't checked
> this syzcaller reproducer but it's probably what it does.
> 
> p9_fd_create doesn't use 'addr' at all so it's safe to create a 9p mount
> for trans=fd with no device name, as Dmitry pointed out
> 

mmh, ok.

> 
>>> On the other hand, virtio, rdma and xen all have the same problem, so
>>> Thomas, please fix them instead :)
>>
>> So just by patching v9fs_mount ?
> 
> If we want to preserve the current behaviour for trans=fd (and I don't
> see why not) we just have to patch all the transports that use the
> device, that is all .create functions but p9_fd_create()
> 
> Basically exactly what you did, just for a few more functions - I
> apparently was a little bit too optimistic thinking we could share
> this check.
> 

Does v9fs_mount() knows the transport ahead? Because in that case it'd
be possible to check if addr!=NULL && trans!=fd then return error

Otherwise, patching all the .create, ok.