linux-kernel - [PATCH 56/93] drm/radeon: fix a rare case of double kfree

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Message-Id: <1360102042-10732-57-git-send-email-herton.krzesinski@canonical.com>
Date:	Tue,  5 Feb 2013 20:06:45 -0200
From:	Herton Ronaldo Krzesinski <herton.krzesinski@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Ilija Hadzic <ihadzic@...earch.bell-labs.com>,
	Herton Ronaldo Krzesinski <herton.krzesinski@...onical.com>,
	Alex Deucher <alexander.deucher@....com>
Subject: [PATCH 56/93] drm/radeon: fix a rare case of double kfree

3.5.7.5 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ilija Hadzic <ihadzic@...earch.bell-labs.com>

commit 1da80cfa8727abf404fcee44d04743febea54069 upstream.

If one (but not both) allocations of p->chunks[].kpage[]
in radeon_cs_parser_init fail, the error path will free
the successfully allocated page, but leave a stale pointer
value in the kpage[] field. This will later cause a
double-free when radeon_cs_parser_fini is called.
This patch fixes the issue by forcing both pointers to NULL
after kfree in the error path.

The circumstances under which the problem happens are very
rare. The card must be AGP and the system must run out of
kmalloc area just at the right time so that one allocation
succeeds, while the other fails.

Signed-off-by: Ilija Hadzic <ihadzic@...earch.bell-labs.com>
Cc: Herton Ronaldo Krzesinski <herton.krzesinski@...onical.com>
Signed-off-by: Alex Deucher <alexander.deucher@....com>
Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski@...onical.com>
---
 drivers/gpu/drm/radeon/radeon_cs.c |    2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/radeon/radeon_cs.c b/drivers/gpu/drm/radeon/radeon_cs.c
index c71652b..a0f3404 100644
--- a/drivers/gpu/drm/radeon/radeon_cs.c
+++ b/drivers/gpu/drm/radeon/radeon_cs.c
@@ -281,6 +281,8 @@ int radeon_cs_parser_init(struct radeon_cs_parser *p, void *data)
 			    p->chunks[p->chunk_ib_idx].kpage[1] == NULL) {
 				kfree(p->chunks[p->chunk_ib_idx].kpage[0]);
 				kfree(p->chunks[p->chunk_ib_idx].kpage[1]);
+				p->chunks[p->chunk_ib_idx].kpage[0] = NULL;
+				p->chunks[p->chunk_ib_idx].kpage[1] = NULL;
 				return -ENOMEM;
 			}
 		}
-- 
1.7.9.5

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