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

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Date:   Fri, 27 Jul 2018 00:15:27 +0200
From:   Dominique Martinet <asmadeus@...ewreck.org>
To:     Tomas Bortoli <tomasbortoli@...il.com>
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

Tomas Bortoli wrote on Thu, Jul 26, 2018:
> > 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.

9p option parsing is all over the place, split in fs/9p/v9fs,
net/9p/client and net/9p/trans_*... Which is actually somewhat of a
problem because that means we can't warn on unused option as each parser
does not know the full subset of options used, so if someone makes a
typo they're on their own to figure it out :/

If you want to factor it in, v9fs_mount does not know which transport is
used, but p9_client_create does know - although the functions/structs
are all static so you need to check clnt->trans_mod->name with strcmp
and I'm honestly not sure that's better than checking in each function..

But, as usual I'm happy as long as it works, so pick your poison :)

-- 
Dominique Martinet