linux-kernel - Re: [PATCH] drm/radeon: fix NULL pointer dereference in UMS mode in radeon_cs_parser

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Date:	Wed, 23 Jan 2013 14:07:00 -0200
From:	Herton Ronaldo Krzesinski <herton.krzesinski@...onical.com>
To:	Shuah Khan <shuah.khan@...com>
Cc:	Ilija Hadzic <ihadzic@...earch.bell-labs.com>, airlied@...ux.ie,
	deathsimple@...afone.de, jglisse@...hat.com, airlied@...hat.com,
	"Deucher, Alexander" <alexander.deucher@....com>,
	Greg KH <gregkh@...uxfoundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	dri-devel@...ts.freedesktop.org, shuahkhan@...il.com
Subject: Re: [PATCH] drm/radeon: fix NULL pointer dereference in UMS mode in
 radeon_cs_parser_fini()

On Thu, Jan 17, 2013 at 10:09:42AM -0700, Shuah Khan wrote:
> On Wed, 2013-01-16 at 21:06 -0600, Ilija Hadzic wrote:
> > Actually, the code path affected by your patch is not executed in UMS mode 
> > at all. Notice that radeon_cs_parser_fini is only called from 
> > radeon_cs_ioctl which is a KMS-only ioctl (see radeon_kms.c).
> > 
> > The equivalent of the fix you are trying to do is in
> > a6b7e1a02b77ab8fe8775d20a88c53d8ba55482e (function patched by that one is 
> > the one used by legacy-CS ioctl), which you should go together 
> > with ff4bd0827764e10a428a9d39e6814c5478863f94 if you are backporting UMS 
> > fixes to 3.7. Both are needed to prevent kernel crashes in UMS mode.
> > 
> > -- Ilija
> 
> Thanks. I will take a look at a6b7e1a02b77ab8fe8775d20a88c53d8ba55482e.
> I sent back-ported ff4bd0827764e10a428a9d39e6814c5478863f94 patch to
> stable and I will back-port and send
> a6b7e1a02b77ab8fe8775d20a88c53d8ba55482e as well.

While at it, also looks like commit
25d8999780f8c1f53928f4a24a09c01550423109 could also be added to stables.
But while looking at it, while the patch itself is correct, I noted that
there is a possibility of double free: if either of the
p->chunks[p->chunk_ib_idx].kpage[] items are non NULL, we will free it in
radeon_cs_parser_init and also when calling one of the fini functions
(radeon_cs_parser_fini or r600_cs_parser_fini). So either we need to set
kpage[n] to NULL after kfree, or just return the error.

> 
> -- Shuah

-- 
[]'s
Herton
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