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Message-ID: <alpine.DEB.2.21.1804191551520.19539@nanos.tec.linutronix.de>
Date: Thu, 19 Apr 2018 16:08:30 +0200 (CEST)
From: Thomas Gleixner <tglx@...utronix.de>
To: Mike Snitzer <snitzer@...hat.com>
cc: NeilBrown <neilb@...e.com>, LKML <linux-kernel@...r.kernel.org>,
Kees Cook <keescook@...omium.org>,
Segher Boessenkool <segher@...nel.crashing.org>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Andrew Morton <akpm@...uxfoundation.org>,
Boris Brezillon <boris.brezillon@...e-electrons.com>,
Richard Weinberger <richard@....at>, David Woodhouse <dwmw2@...radead.org>,
Alasdair Kergon <agk@...hat.com>, Anton Vorontsov <anton@...msg.org>,
Colin Cross <ccross@...roid.com>, Tony Luck <tony.luck@...el.com>
Subject: Re: [patch V2 7/8] dm verity fec: Check result of init_rs()
On Thu, 19 Apr 2018, Mike Snitzer wrote:
> On Thu, Apr 19 2018 at 6:04am -0400,
> Thomas Gleixner <tglx@...utronix.de> wrote:
>
> > From: Thomas Gleixner <tglx@...utronix.de>
> >
> > The allocation of the reed solomon control structure can fail, but
> > fec_alloc_bufs() ignores that and subsequent operations in dm verity use
> > the potential NULL pointer unconditionally.
> >
> > Add a proper check and abort if init_rs() fails.
>
> This changelog makes little sense: init_rs() isn't in play relative to
> this patch.
fio->rs = mempool_alloc(v->fec->rs_pool, GFP_NOIO);
f->rs_pool = mempool_create(num_online_cpus(), fec_rs_alloc,
fec_rs_free, (void *) v);
static void *fec_rs_alloc(gfp_t gfp_mask, void *pool_data)
{
struct dm_verity *v = (struct dm_verity *)pool_data;
return init_rs(8, 0x11d, 0, 1, v->fec->roots);
}
So init_rs() is part of the chain, right?
Yes. I missed the NOIO part. But....
> And it runs counter to this commit's changelog:
>
> commit 34c96507e8f6be497c15497be05f489fb34c5880
> Author: NeilBrown <neilb@...e.com>
> Date: Mon Apr 10 12:13:00 2017 +1000
>
> dm verity fec: fix GFP flags used with mempool_alloc()
>
> mempool_alloc() cannot fail for GFP_NOIO allocation, so there is no
> point testing for failure.
>
> One place the code tested for failure was passing "0" as the GFP
> flags. This is most unusual and is probably meant to be GFP_NOIO,
> so that is changed.
>
> Also, allocation from ->extra_pool and ->prealloc_pool are repeated
> before releasing the previous allocation. This can deadlock if the code
> is servicing a write under high memory pressure. To avoid deadlocks,
> change these to use GFP_NOWAIT and leave the error handling in place.
>
> Signed-off-by: NeilBrown <neilb@...e.com>
> Signed-off-by: Mike Snitzer <snitzer@...hat.com>
>
> Seems there is no real need for this patch. Neil, what do you think?
The analysis above forgot to look at the mempool->alloc() callback. So yes,
while the NOIO is good at the mempool level, but init_rs() uses GPF_KERNEL
so there might be a different can of wurms lurking.
Thanks,
tglx
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