avcodec/dvdsubdec: fix out of bounds accesses

The code blindly trusted buffer offsets read from the file in the RLE
decoder. Explicitly check the offset. Also error out on other RLE
decoding errors.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

1 files changed, 9 insertions, 4 deletions

diff --git a/libavcodec/dvdsubdec.c b/libavcodec/dvdsubdec.c
index c7d85a6a1f..2423cadcaa 100644
--- a/libavcodec/dvdsubdec.c
+++ b/libavcodec/dvdsubdec.c
@@ -108,6 +108,9 @@ static int decode_rle(uint8_t *bitmap, int linesize, int w, int h,
     int x, y, len, color;
     uint8_t *d;
 
+    if (start >= buf_size)
+        return -1;
+
     bit_len = (buf_size - start) * 8;
     init_get_bits(&gb, buf + start, bit_len);
 
@@ -359,10 +362,12 @@ static int decode_dvd_subtitles(DVDSubContext *ctx, AVSubtitle *sub_header,
                 sub_header->rects[0] = av_mallocz(sizeof(AVSubtitleRect));
                 sub_header->num_rects = 1;
                 sub_header->rects[0]->pict.data[0] = bitmap;
-                decode_rle(bitmap, w * 2, w, (h + 1) / 2,
-                           buf, offset1, buf_size, is_8bit);
-                decode_rle(bitmap + w, w * 2, w, h / 2,
-                           buf, offset2, buf_size, is_8bit);
+                if (decode_rle(bitmap, w * 2, w, (h + 1) / 2,
+                               buf, offset1, buf_size, is_8bit) < 0)
+                    goto fail;
+                if (decode_rle(bitmap + w, w * 2, w, h / 2,
+                               buf, offset2, buf_size, is_8bit) < 0)
+                    goto fail;
                 sub_header->rects[0]->pict.data[1] = av_mallocz(AVPALETTE_SIZE);
                 if (is_8bit) {
                     if (!yuv_palette)