linux-kernel - Re: [PATCH] bttv: fix mutex use before init

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Date:	Mon, 13 Dec 2010 16:30:24 -0800
From:	Brandon Philips <brandon@...p.org>
To:	Torsten Kaiser <just.for.lkml@...glemail.com>
Cc:	Dave Young <hidave.darkstar@...il.com>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	Mauro Carvalho Chehab <mchehab@...radead.org>,
	Guennadi Liakhovetski <g.liakhovetski@....de>,
	Chris Clayton <chris2553@...glemail.com>
Subject: Re: [PATCH] bttv: fix mutex use before init

On 17:13 Sun 12 Dec 2010, Torsten Kaiser wrote:
>  * change &fh->cap.vb_lock in bttv_open() AND radio_open() to
> &btv->init.cap.vb_lock
>  * add a mutex_init(&btv->init.cap.vb_lock) to the setup of init in bttv_probe()

That seems like a reasonable suggestion. An openSUSE user submitted this
bug to our tracker too. Here is the patch I am having him test.

Would you mind testing it?

>From 456dc0ce36db523c4c0c8a269f4eec43a72de1dc Mon Sep 17 00:00:00 2001
From: Brandon Philips <bphilips@...e.de>
Date: Mon, 13 Dec 2010 16:21:55 -0800
Subject: [PATCH] bttv: fix locking for btv->init

Fix locking for the btv->init by using btv->init.cap.vb_lock and in the
process fix uninitialized deref introduced in c37db91fd0d.

Signed-off-by: Brandon Philips <bphilips@...e.de>
---
 drivers/media/video/bt8xx/bttv-driver.c |   24 +++++++++++++-----------
 1 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/drivers/media/video/bt8xx/bttv-driver.c b/drivers/media/video/bt8xx/bttv-driver.c
index a529619..e656424 100644
--- a/drivers/media/video/bt8xx/bttv-driver.c
+++ b/drivers/media/video/bt8xx/bttv-driver.c
@@ -2391,16 +2391,11 @@ static int setup_window_lock(struct bttv_fh *fh, struct bttv *btv,
 	fh->ov.field    = win->field;
 	fh->ov.setup_ok = 1;
 
-	/*
-	 * FIXME: btv is protected by btv->lock mutex, while btv->init
-	 *	  is protected by fh->cap.vb_lock. This seems to open the
-	 *	  possibility for some race situations. Maybe the better would
-	 *	  be to unify those locks or to use another way to store the
-	 *	  init values that will be consumed by videobuf callbacks
-	 */
+	mutex_lock(&btv->init.cap.vb_lock);
 	btv->init.ov.w.width   = win->w.width;
 	btv->init.ov.w.height  = win->w.height;
 	btv->init.ov.field     = win->field;
+	mutex_unlock(&btv->init.cap.vb_lock);
 
 	/* update overlay if needed */
 	retval = 0;
@@ -2620,9 +2615,11 @@ static int bttv_s_fmt_vid_cap(struct file *file, void *priv,
 	fh->cap.last         = V4L2_FIELD_NONE;
 	fh->width            = f->fmt.pix.width;
 	fh->height           = f->fmt.pix.height;
+	mutex_lock(&btv->init.cap.vb_lock);
 	btv->init.fmt        = fmt;
 	btv->init.width      = f->fmt.pix.width;
 	btv->init.height     = f->fmt.pix.height;
+	mutex_unlock(&btv->init.cap.vb_lock);
 	mutex_unlock(&fh->cap.vb_lock);
 
 	return 0;
@@ -2855,6 +2852,7 @@ static int bttv_s_fbuf(struct file *file, void *f,
 
 	retval = 0;
 	fh->ovfmt = fmt;
+	mutex_lock(&btv->init.cap.vb_lock);
 	btv->init.ovfmt = fmt;
 	if (fb->flags & V4L2_FBUF_FLAG_OVERLAY) {
 		fh->ov.w.left   = 0;
@@ -2876,6 +2874,7 @@ static int bttv_s_fbuf(struct file *file, void *f,
 			retval = bttv_switch_overlay(btv, fh, new);
 		}
 	}
+	mutex_unlock(&btv->init.cap.vb_lock);
 	mutex_unlock(&fh->cap.vb_lock);
 	return retval;
 }
@@ -3141,6 +3140,7 @@ static int bttv_s_crop(struct file *file, void *f, struct v4l2_crop *crop)
 	fh->do_crop = 1;
 
 	mutex_lock(&fh->cap.vb_lock);
+	mutex_lock(&btv->init.cap.vb_lock);
 
 	if (fh->width < c.min_scaled_width) {
 		fh->width = c.min_scaled_width;
@@ -3158,6 +3158,7 @@ static int bttv_s_crop(struct file *file, void *f, struct v4l2_crop *crop)
 		btv->init.height = c.max_scaled_height;
 	}
 
+	mutex_unlock(&btv->init.cap.vb_lock);
 	mutex_unlock(&fh->cap.vb_lock);
 
 	return 0;
@@ -3302,9 +3303,9 @@ static int bttv_open(struct file *file)
 	 * Let's first copy btv->init at fh, holding cap.vb_lock, and then work
 	 * with the rest of init, holding btv->lock.
 	 */
-	mutex_lock(&fh->cap.vb_lock);
+	mutex_lock(&btv->init.cap.vb_lock);
 	*fh = btv->init;
-	mutex_unlock(&fh->cap.vb_lock);
+	mutex_unlock(&btv->init.cap.vb_lock);
 
 	fh->type = type;
 	fh->ov.setup_ok = 0;
@@ -3502,9 +3503,9 @@ static int radio_open(struct file *file)
 	if (unlikely(!fh))
 		return -ENOMEM;
 	file->private_data = fh;
-	mutex_lock(&fh->cap.vb_lock);
+	mutex_lock(&btv->init.cap.vb_lock);
 	*fh = btv->init;
-	mutex_unlock(&fh->cap.vb_lock);
+	mutex_unlock(&btv->init.cap.vb_lock);
 
 	mutex_lock(&btv->lock);
 	v4l2_prio_open(&btv->prio, &fh->prio);
@@ -4489,6 +4490,7 @@ static int __devinit bttv_probe(struct pci_dev *dev,
 	btv->opt_coring     = coring;
 
 	/* fill struct bttv with some useful defaults */
+	mutex_init(&btv->init.cap.vb_lock);
 	btv->init.btv         = btv;
 	btv->init.ov.w.width  = 320;
 	btv->init.ov.w.height = 240;
-- 
1.7.3.1

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