linux-kernel - [PATCH 4/4] drivers/media/video: Eliminate use after free

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Date:	Sat, 15 May 2010 11:46:54 +0200 (CEST)
From:	Julia Lawall <julia@...u.dk>
To:	Mauro Carvalho Chehab <mchehab@...radead.org>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: [PATCH 4/4] drivers/media/video: Eliminate use after free

From: Julia Lawall <julia@...u.dk>

The error value is saved in a new local variable err before freeing the
containing structure.

A simplified version of the semantic match that finds this problem is as
follows: (http://coccinelle.lip6.fr/)

// <smpl>
@free@
expression E;
position p;
@@
kfree@p(E)

@@
expression free.E, subE<=free.E, E1;
position free.p;
@@

  kfree@p(E)
  ...
(
  subE = E1
|
* E
)
// </smpl>

Signed-off-by: Julia Lawall <julia@...u.dk>

---
 drivers/media/video/mem2mem_testdev.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/media/video/mem2mem_testdev.c b/drivers/media/video/mem2mem_testdev.c
index baf211b..fb73f34 100644
--- a/drivers/media/video/mem2mem_testdev.c
+++ b/drivers/media/video/mem2mem_testdev.c
@@ -858,6 +858,7 @@ static int m2mtest_open(struct file *file)
 {
 	struct m2mtest_dev *dev = video_drvdata(file);
 	struct m2mtest_ctx *ctx = NULL;
+	int err;
 
 	ctx = kzalloc(sizeof *ctx, GFP_KERNEL);
 	if (!ctx)
@@ -871,8 +872,9 @@ static int m2mtest_open(struct file *file)
 
 	ctx->m2m_ctx = v4l2_m2m_ctx_init(ctx, dev->m2m_dev, queue_init);
 	if (IS_ERR(ctx->m2m_ctx)) {
+		err = PTR_ERR(ctx->m2m_ctx);
 		kfree(ctx);
-		return PTR_ERR(ctx->m2m_ctx);
+		return err;
 	}
 
 	atomic_inc(&dev->num_inst);
--
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