[PATCH v2] media: uvcvideo: read bulk URBs after maxPayloadSize

[Julian Meyer <julianmeyer2000@gmail.com>]

This fixes a bug that caused certain Realtek cameras to crash.

The camera would send additional UVC payloads after the maxPayloadSize
was reached. This patch modifies uvc_video_decode_bulk such that it
continues reading payloads when it reaches the maxPayloadSize if there
is more data left.

Signed-off-by: Julian Meyer <julianmeyer2000@gmail.com>
---
 drivers/media/usb/uvc/uvc_video.c | 85 +++++++++++++++++++++++--------
 1 file changed, 63 insertions(+), 22 deletions(-)

diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
index 8fa77a81dd7f..9e07cc516796 100644
--- a/drivers/media/usb/uvc/uvc_video.c
+++ b/drivers/media/usb/uvc/uvc_video.c
@@ -1374,31 +1374,24 @@ static void uvc_video_decode_isoc(struct uvc_urb *uvc_urb,
 	}
 }
 
-static void uvc_video_decode_bulk(struct uvc_urb *uvc_urb,
-			struct uvc_buffer *buf, struct uvc_buffer *meta_buf)
+static int uvc_video_decode_bulk_single(struct uvc_streaming *stream,
+	struct uvc_buffer *buf, struct uvc_buffer *meta_buf,
+	struct uvc_urb *uvc_urb, u8 **mem, int *len)
 {
-	struct urb *urb = uvc_urb->urb;
-	struct uvc_streaming *stream = uvc_urb->stream;
-	u8 *mem;
-	int len, ret;
+	unsigned int bytes_left;
+	int ret;
 
-	/*
-	 * Ignore ZLPs if they're not part of a frame, otherwise process them
-	 * to trigger the end of payload detection.
-	 */
-	if (urb->actual_length == 0 && stream->bulk.header_size == 0)
-		return;
+	int length_removed = 0;
 
-	mem = urb->transfer_buffer;
-	len = urb->actual_length;
-	stream->bulk.payload_size += len;
+	struct urb *urb = uvc_urb->urb;
+	unsigned int max_size = stream->bulk.max_payload_size;
 
 	/* If the URB is the first of its payload, decode and save the
 	 * header.
 	 */
 	if (stream->bulk.header_size == 0 && !stream->bulk.skip_payload) {
 		do {
-			ret = uvc_video_decode_start(stream, buf, mem, len);
+			ret = uvc_video_decode_start(stream, buf, *mem, *len);
 			if (ret == -EAGAIN)
 				uvc_video_next_buffers(stream, &buf, &meta_buf);
 		} while (ret == -EAGAIN);
@@ -1407,13 +1400,15 @@ static void uvc_video_decode_bulk(struct uvc_urb *uvc_urb,
 		if (ret < 0 || buf == NULL) {
 			stream->bulk.skip_payload = 1;
 		} else {
-			memcpy(stream->bulk.header, mem, ret);
+			memcpy(stream->bulk.header, *mem, ret);
 			stream->bulk.header_size = ret;
 
-			uvc_video_decode_meta(stream, meta_buf, mem, ret);
+			uvc_video_decode_meta(stream, meta_buf, *mem, ret);
 
-			mem += ret;
-			len -= ret;
+			*mem += ret;
+			length_removed += ret;
+			*len -= ret;
+			stream->bulk.payload_size += ret;
 		}
 	}
 
@@ -1423,8 +1418,22 @@ static void uvc_video_decode_bulk(struct uvc_urb *uvc_urb,
 	 */
 
 	/* Prepare video data for processing. */
-	if (!stream->bulk.skip_payload && buf != NULL)
-		uvc_video_decode_data(uvc_urb, buf, mem, len);
+	if (!stream->bulk.skip_payload && buf != NULL) {
+		bytes_left = min((unsigned int) *len,
+			max_size - stream->bulk.payload_size);
+
+		stream->bulk.payload_size += bytes_left;
+
+		uvc_video_decode_data(uvc_urb, buf, *mem, bytes_left);
+
+		*len -= bytes_left;
+		*mem += bytes_left;
+		length_removed = bytes_left;
+	} else {
+		stream->bulk.payload_size += *len;
+		length_removed = *len;
+		*len = 0;
+	}
 
 	/* Detect the payload end by a URB smaller than the maximum size (or
 	 * a payload size equal to the maximum) and process the header again.
@@ -1442,6 +1451,38 @@ static void uvc_video_decode_bulk(struct uvc_urb *uvc_urb,
 		stream->bulk.skip_payload = 0;
 		stream->bulk.payload_size = 0;
 	}
+
+	return length_removed;
+}
+
+static void uvc_video_decode_bulk(struct uvc_urb *uvc_urb,
+			struct uvc_buffer *buf, struct uvc_buffer *meta_buf)
+{
+	struct urb *urb = uvc_urb->urb;
+	struct uvc_streaming *stream = uvc_urb->stream;
+	u8 *mem;
+	int len;
+	int len_processed;
+
+	/*
+	 * Ignore ZLPs if they're not part of a frame, otherwise process them
+	 * to trigger the end of payload detection.
+	 */
+	if (urb->actual_length == 0 && stream->bulk.header_size == 0)
+		return;
+
+	mem = urb->transfer_buffer;
+	len = urb->actual_length;
+
+	while (len > 0) {
+		len_processed = uvc_video_decode_bulk_single(stream, buf,
+			meta_buf, uvc_urb, &mem, &len);
+
+		// if we don't process anything, we break out of the decode loop
+		if (len_processed == 0) {
+			return
+		}
+	}
 }
 
 static void uvc_video_encode_bulk(struct uvc_urb *uvc_urb,
-- 
2.26.1