linux-kernel - [PATCH 3.16 236/254] [media] V4L2: fix VIDIOC_CREATE_BUFS 32-bit compatibility mode data copy-back

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Message-ID: <lsq.1519831218.185997385@decadent.org.uk>
Date:   Wed, 28 Feb 2018 15:20:18 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Mauro Carvalho Chehab" <mchehab@....samsung.com>,
        "Laurent Pinchart" <laurent.pinchart@...asonboard.com>,
        "Guennadi Liakhovetski" <g.liakhovetski@....de>
Subject: [PATCH 3.16 236/254] [media] V4L2: fix VIDIOC_CREATE_BUFS 32-bit
 compatibility mode data copy-back

3.16.55-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Guennadi Liakhovetski <g.liakhovetski@....de>

commit 6ed9b28504326f8cf542e6b68245b2f7ce009216 upstream.

Similar to an earlier patch, fixing reading user-space data for the
VIDIOC_CREATE_BUFS ioctl() in 32-bit compatibility mode, this patch fixes
writing back of the possibly modified struct to the user. However, unlike
the former bug, this one is much less harmful, because it only results in
the kernel failing to write the .type field back to the user, but in fact
this is likely unneeded, because the kernel will hardly want to change
that field. Therefore this bug is more of a theoretical nature.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@....de>
Acked-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@....samsung.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/media/v4l2-core/v4l2-compat-ioctl32.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

--- a/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
+++ b/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
@@ -222,6 +222,9 @@ static int get_v4l2_create32(struct v4l2
 
 static int __put_v4l2_format32(struct v4l2_format *kp, struct v4l2_format32 __user *up)
 {
+	if (put_user(kp->type, &up->type))
+		return -EFAULT;
+
 	switch (kp->type) {
 	case V4L2_BUF_TYPE_VIDEO_CAPTURE:
 	case V4L2_BUF_TYPE_VIDEO_OUTPUT:
@@ -248,8 +251,7 @@ static int __put_v4l2_format32(struct v4
 
 static int put_v4l2_format32(struct v4l2_format *kp, struct v4l2_format32 __user *up)
 {
-	if (!access_ok(VERIFY_WRITE, up, sizeof(struct v4l2_format32)) ||
-		put_user(kp->type, &up->type))
+	if (!access_ok(VERIFY_WRITE, up, sizeof(struct v4l2_format32)))
 		return -EFAULT;
 	return __put_v4l2_format32(kp, up);
 }
@@ -257,8 +259,8 @@ static int put_v4l2_format32(struct v4l2
 static int put_v4l2_create32(struct v4l2_create_buffers *kp, struct v4l2_create_buffers32 __user *up)
 {
 	if (!access_ok(VERIFY_WRITE, up, sizeof(struct v4l2_create_buffers32)) ||
-	    copy_to_user(up, kp, offsetof(struct v4l2_create_buffers32, format.fmt)))
-			return -EFAULT;
+	    copy_to_user(up, kp, offsetof(struct v4l2_create_buffers32, format)))
+		return -EFAULT;
 	return __put_v4l2_format32(&kp->format, &up->format);
 }