linux-kernel - [PATCH] intel, gma500, lvds: Fix use after free on psb_intel_lvds

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Date:	Sat, 14 Jan 2012 20:59:33 +0100 (CET)
From:	Jesper Juhl <jj@...osbits.net>
To:	linux-kernel@...r.kernel.org
cc:	dri-devel@...ts.freedesktop.org,
	Octavian Purdila <octavian.purdila@...el.com>,
	Dave Airlie <airlied@...hat.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Alan Cox <alan@...ux.intel.com>,
	David Airlie <airlied@...ux.ie>, Eric Anholt <eric@...olt.net>,
	Jesse Barnes <jesse.barnes@...el.com>
Subject: [PATCH] intel, gma500, lvds: Fix use after free on
 psb_intel_lvds_init()

In psb_intel_lvds_init(), if we fail to allocate memory for
'psb_intel_connector' we free the memory we previously allocated for
'psb_intel_encoder', but we then proceed to use that free'd pointer
when we do 'psb_intel_encoder->dev_priv = lvds_priv;'.

I believe the proper way to handle this is to simply return after the
allocation for 'psb_intel_connector' has failed. That is what this
patch does.

While I was there anyway, I also removed the pointless 'if
(psb_intel_connector)' before freeing it at the 'failed_connector:'
label - kfree() deals gracefully with NULL pointers, so it is not
needed.

Signed-off-by: Jesper Juhl <jj@...osbits.net>
---
 drivers/gpu/drm/gma500/psb_intel_lvds.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

 I considered adding a new label at the end and use a goto instead, but
 settled on this minimal solution. If consolidating all exits from the 
 function is prefered then I can rework the patch to do that
 instead. Just let me know.

 Patch is compile tested only since I don't have the hardware to
 actually test it properly.

diff --git a/drivers/gpu/drm/gma500/psb_intel_lvds.c b/drivers/gpu/drm/gma500/psb_intel_lvds.c
index a25e4ca..7d23ef9 100644
--- a/drivers/gpu/drm/gma500/psb_intel_lvds.c
+++ b/drivers/gpu/drm/gma500/psb_intel_lvds.c
@@ -725,6 +725,7 @@ void psb_intel_lvds_init(struct drm_device *dev,
 	if (!psb_intel_connector) {
 		kfree(psb_intel_encoder);
 		dev_err(dev->dev, "psb_intel_connector allocation error\n");
+		return;
 	}

 	lvds_priv = kzalloc(sizeof(struct psb_intel_lvds_priv), GFP_KERNEL);
@@ -862,7 +863,6 @@ failed_blc_i2c:
 	drm_encoder_cleanup(encoder);
 	drm_connector_cleanup(connector);
 failed_connector:
-	if (psb_intel_connector)
-		kfree(psb_intel_connector);
+	kfree(psb_intel_connector);
 }

-- 
1.7.8.3

-- 
Jesper Juhl <jj@...osbits.net>       http://www.chaosbits.net/
Don't top-post http://www.catb.org/jargon/html/T/top-post.html
Plain text mails only, please.

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