linux-kernel - Re: [V9fs-developer] [PATCH 2/6] 9p: Replace the fidlist with an IDR

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Message-ID: <20180711130854.GB23640@bombadil.infradead.org>
Date:   Wed, 11 Jul 2018 06:08:54 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Dominique Martinet <asmadeus@...ewreck.org>
Cc:     v9fs-developer@...ts.sourceforge.net,
        Latchesar Ionkov <lucho@...kov.net>,
        Eric Van Hensbergen <ericvh@...il.com>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Ron Minnich <rminnich@...dia.gov>
Subject: Re: [V9fs-developer] [PATCH 2/6] 9p: Replace the fidlist with an IDR

On Wed, Jul 11, 2018 at 02:58:12PM +0200, Dominique Martinet wrote:
> > I don't understand your assertion that this is a change of behaviour.
> > The implementation of p9_idpool_get() uses idr_alloc(), not
> > idr_alloc_cyclic(), so I don't believe I've changed which FID would
> > be allocated.
> 
> Hmm, I just tried mounting something with ganesha and that broke because
> it received fid=1730858632 in a TATTACH request, so something in the
> patch series made some big fid happens.
> 
> If you say this isn't intented though this needs debugging, I'm glad I
> brought this up :P
> 
> (Note that it really should be fine if it is random within the pool, I
> have notified the current developpers of the problem)

Heh, unintended protocol fuzzing ;-)

I see the problem; need to initialise fid->fid to 0 before calling
idr_alloc_u32.  I'd misread:

        memset(&fid->qid, 0, sizeof(struct p9_qid));
as
        memset(fid, 0, sizeof(struct p9_fid));

so I thought fid->fid was already 0.  I'll fix that up, thanks!