drivers: video: sw_generator: modify video_sw_generator_fill_colorbar()

Add a check for the array size to avoid overwriting unrelated memory when
the buffer is too small for the full format. It first check if there is
enough buffer for one line, and fill it programmatically. Then, it will
try to duplicate that line over the entire buffer, in the limit of the
room available.

Signed-off-by: Josuah Demangeon <me@josuah.net>

Author: josuah

drivers/video/video_sw_generator.c

@@ -11,6 +11,7 @@
 #include <zephyr/drivers/video-controls.h>
 #include <zephyr/logging/log.h>
 #include <zephyr/sys/util.h>
+#include <zephyr/sys/byteorder.h>
 
 #include "video_ctrls.h"
 #include "video_device.h"
@@ -118,29 +119,50 @@ uint32_t xrgb32_colorbar_value[] = {
 	0xFF00FF00, 0xFF00FFFF, 0xFFFFFF00, 0xFFFFFFFF,
 };
 
+static inline int video_sw_generator_get_color_idx(uint16_t w, uint16_t width, bool hflip)
+{
+	/* If hflip is on, start from the right instead */
+	w = (hflip) ? (width - w - 1) : (w);
+
+	/* Downscale from w/width to #/8 */
+	return 8 * w / width;
+}
+
 static void video_sw_generator_fill_colorbar(struct video_sw_generator_data *data,
 					     struct video_buffer *vbuf)
 {
 	int bw = data->fmt.width / 8;
-	int h, w, i = 0;
-
-	for (h = 0; h < data->fmt.height; h++) {
-		for (w = 0; w < data->fmt.width; w++) {
-			int color_idx = data->ctrls.hflip.val ? 7 - w / bw : w / bw;
-			if (data->fmt.pixelformat == VIDEO_PIX_FMT_RGB565) {
-				uint16_t *pixel = (uint16_t *)&vbuf->buffer[i];
-				*pixel = rgb565_colorbar_value[color_idx];
-				i += 2;
-			} else if (data->fmt.pixelformat == VIDEO_PIX_FMT_XRGB32) {
-				uint32_t *pixel = (uint32_t *)&vbuf->buffer[i];
-				*pixel = xrgb32_colorbar_value[color_idx];
-				i += 4;
-			}
+	struct video_format *fmt = &data->fmt;
+	size_t pitch = fmt->width * video_bits_per_pixel(fmt->pixelformat) / BITS_PER_BYTE;
+	bool hflip = data->ctrls.hflip.val;
+
+	vbuf->bytesused = 0;
+
+	/* Generate the first line of data */
+	for (int w = 0, i = 0; w < data->fmt.width; w++) {
+		int color_idx = video_sw_generator_get_color_idx(w, width, hflip);
+
+		if (data->fmt.pixelformat == VIDEO_PIX_FMT_RGB565) {
+			uint16_t *pixel = (uint16_t *)&vbuf->buffer[i];
+			*pixel = sys_cpu_to_le16(rgb565_colorbar_value[color_idx]);
+		} else if (data->fmt.pixelformat == VIDEO_PIX_FMT_XRGB32) {
+			uint32_t *pixel = (uint32_t *)&vbuf->buffer[i];
+			*pixel = sys_cpu_to_le32(xrgb32_colorbar_value[color_idx]);
 		}
+		i += video_bits_per_pixel(data->fmt.pixelformat) / BITS_PER_BYTE;
+	}
+
+	/* Duplicate the first line all over the buffer */
+	for (int h = 1; h < data->fmt.height; h++) {
+		if (vbuf->size < vbuf->bytesused + pitch) {
+			break;
+		}
+
+		memcpy(vbuf->buffer + h * pitch, vbuf->buffer, pitch);
+		vbuf->bytesused += pitch;
 	}
 
 	vbuf->timestamp = k_uptime_get_32();
-	vbuf->bytesused = i;
 	vbuf->line_offset = 0;
 }