[PATCH v2 1/1] v4l: compat: Prevent allocating excessive amounts of memory

[Sakari Ailus <sakari.ailus@linux.intel.com>]

get_v4l2_ext_controls32() is used to convert the 32-bit compat struct into
native 64-bit representation. The function multiplies the array length by
the entry length before validating size. Perform the size validation
first.

Also use unsigned values for size computation.

Make similar changes to get_v4l2_buffer32() for multi-plane buffers.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
---
since v1:

- Use unsigned loop variables.

- Count from zero upwards rather than downwards until zero.

 drivers/media/v4l2-core/v4l2-compat-ioctl32.c | 30 +++++++++++++++------------
 1 file changed, 17 insertions(+), 13 deletions(-)

diff --git a/drivers/media/v4l2-core/v4l2-compat-ioctl32.c b/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
index bacecbd..eac9565 100644
--- a/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
+++ b/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
@@ -409,7 +409,6 @@ static int get_v4l2_buffer32(struct v4l2_buffer *kp, struct v4l2_buffer32 __user
 	struct v4l2_plane32 __user *uplane32;
 	struct v4l2_plane __user *uplane;
 	compat_caddr_t p;
-	int num_planes;
 	int ret;
 
 	if (!access_ok(VERIFY_READ, up, sizeof(struct v4l2_buffer32)) ||
@@ -429,12 +428,15 @@ static int get_v4l2_buffer32(struct v4l2_buffer *kp, struct v4l2_buffer32 __user
 			return -EFAULT;
 
 	if (V4L2_TYPE_IS_MULTIPLANAR(kp->type)) {
-		num_planes = kp->length;
-		if (num_planes == 0) {
+		unsigned int num_planes;
+
+		if (kp->length == 0) {
 			kp->m.planes = NULL;
 			/* num_planes == 0 is legal, e.g. when userspace doesn't
 			 * need planes array on DQBUF*/
 			return 0;
+		} else if (kp->length > VIDEO_MAX_PLANES) {
+			return -EINVAL;
 		}
 
 		if (get_user(p, &up->m.planes))
@@ -442,16 +444,16 @@ static int get_v4l2_buffer32(struct v4l2_buffer *kp, struct v4l2_buffer32 __user
 
 		uplane32 = compat_ptr(p);
 		if (!access_ok(VERIFY_READ, uplane32,
-				num_planes * sizeof(struct v4l2_plane32)))
+				kp->length * sizeof(struct v4l2_plane32)))
 			return -EFAULT;
 
 		/* We don't really care if userspace decides to kill itself
 		 * by passing a very big num_planes value */
-		uplane = compat_alloc_user_space(num_planes *
-						sizeof(struct v4l2_plane));
+		uplane = compat_alloc_user_space(kp->length *
+						 sizeof(struct v4l2_plane));
 		kp->m.planes = (__force struct v4l2_plane *)uplane;
 
-		while (--num_planes >= 0) {
+		for (num_planes = 0; num_planes < kp->length; num_planes++) {
 			ret = get_v4l2_plane32(uplane, uplane32, kp->memory);
 			if (ret)
 				return ret;
@@ -665,7 +667,7 @@ static int get_v4l2_ext_controls32(struct v4l2_ext_controls *kp, struct v4l2_ext
 {
 	struct v4l2_ext_control32 __user *ucontrols;
 	struct v4l2_ext_control __user *kcontrols;
-	int n;
+	unsigned int n;
 	compat_caddr_t p;
 
 	if (!access_ok(VERIFY_READ, up, sizeof(struct v4l2_ext_controls32)) ||
@@ -675,20 +677,22 @@ static int get_v4l2_ext_controls32(struct v4l2_ext_controls *kp, struct v4l2_ext
 		copy_from_user(kp->reserved, up->reserved,
 			       sizeof(kp->reserved)))
 			return -EFAULT;
-	n = kp->count;
-	if (n == 0) {
+	if (kp->count == 0) {
 		kp->controls = NULL;
 		return 0;
+	} else if (kp->count > V4L2_CID_MAX_CTRLS) {
+		return -EINVAL;
 	}
 	if (get_user(p, &up->controls))
 		return -EFAULT;
 	ucontrols = compat_ptr(p);
 	if (!access_ok(VERIFY_READ, ucontrols,
-			n * sizeof(struct v4l2_ext_control32)))
+			kp->count * sizeof(struct v4l2_ext_control32)))
 		return -EFAULT;
-	kcontrols = compat_alloc_user_space(n * sizeof(struct v4l2_ext_control));
+	kcontrols = compat_alloc_user_space(kp->count *
+					    sizeof(struct v4l2_ext_control));
 	kp->controls = (__force struct v4l2_ext_control *)kcontrols;
-	while (--n >= 0) {
+	for (n = 0; n < kp->count; n++) {
 		u32 id;
 
 		if (copy_in_user(kcontrols, ucontrols, sizeof(*ucontrols)))
-- 
2.7.4