linux-kernel - Re: possible use-after-free in drivers/mtd/ubi/wl.c: erase

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Message-ID: <CA+5PVA7BowJwum9TLCdLUfS7b6ifRQtkw3vf0rhO4+TwyLD6jg@mail.gmail.com>
Date:	Wed, 4 Jan 2012 12:33:11 -0500
From:	Josh Boyer <jwboyer@...il.com>
To:	Emese Revfy <re.emese@...il.com>
Cc:	dedekind1@...il.com, dwmw2@...radead.org,
	linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: possible use-after-free in drivers/mtd/ubi/wl.c: erase_worker

On Tue, Jan 3, 2012 at 6:34 PM, Emese Revfy <re.emese@...il.com> wrote:
> Hi,
>
> I think I found a potential problem in drivers/mtd/ubi/wl.c in
> erase_worker():
>
> 1050         ubi_err("failed to erase PEB %d, error %d", pnum, err);
> 1051         kfree(wl_wrk);
> 1052         kmem_cache_free(ubi_wl_entry_slab, e);
> 1053
> 1054         if (err == -EINTR || err == -ENOMEM || err == -EAGAIN ||
> 1055             err == -EBUSY) {
> 1056                 int err1;
> 1057
> 1058                 /* Re-schedule the LEB for erasure */
> 1059                 err1 = schedule_erase(ubi, e, 0);
>
> The pointer e is freed at line 1052 (kmem_cache_free), but
> later it is passed to schedule_erase which will eventually call
> erase_worker where it will be dereferenced and/or freed again.

Yes.  That does seem to be a problem.  Care to create a patch that solves this
by deferring the frees until after the err variable is checked?

josh
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