avcodec/wmv2dec: Check end of bitstream in parse_mb_skip() and ff_wmv2_decode_mb()

Fixes: Timeout
Fixes: 3200/clusterfuzz-testcase-5750022136135680

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/wmv2dec.c

@@ -30,7 +30,7 @@
 #include "wmv2.h"
 
 
-static void parse_mb_skip(Wmv2Context *w)
+static int parse_mb_skip(Wmv2Context *w)
 {
     int mb_x, mb_y;
     MpegEncContext *const s = &w->s;
@@ -45,6 +45,8 @@ static void parse_mb_skip(Wmv2Context *w)
                     MB_TYPE_16x16 | MB_TYPE_L0;
         break;
     case SKIP_TYPE_MPEG:
+        if (get_bits_left(&s->gb) < s->mb_height * s->mb_width)
+            return AVERROR_INVALIDDATA;
         for (mb_y = 0; mb_y < s->mb_height; mb_y++)
             for (mb_x = 0; mb_x < s->mb_width; mb_x++)
                 mb_type[mb_y * s->mb_stride + mb_x] =
@@ -52,6 +54,8 @@ static void parse_mb_skip(Wmv2Context *w)
         break;
     case SKIP_TYPE_ROW:
         for (mb_y = 0; mb_y < s->mb_height; mb_y++) {
+            if (get_bits_left(&s->gb) < 1)
+                return AVERROR_INVALIDDATA;
             if (get_bits1(&s->gb)) {
                 for (mb_x = 0; mb_x < s->mb_width; mb_x++)
                     mb_type[mb_y * s->mb_stride + mb_x] =
@@ -65,6 +69,8 @@ static void parse_mb_skip(Wmv2Context *w)
         break;
     case SKIP_TYPE_COL:
         for (mb_x = 0; mb_x < s->mb_width; mb_x++) {
+            if (get_bits_left(&s->gb) < 1)
+                return AVERROR_INVALIDDATA;
             if (get_bits1(&s->gb)) {
                 for (mb_y = 0; mb_y < s->mb_height; mb_y++)
                     mb_type[mb_y * s->mb_stride + mb_x] =
@@ -77,6 +83,7 @@ static void parse_mb_skip(Wmv2Context *w)
         }
         break;
     }
+    return 0;
 }
 
 static int decode_ext_header(Wmv2Context *w)
@@ -170,9 +177,12 @@ int ff_wmv2_decode_secondary_picture_header(MpegEncContext *s)
         }
     } else {
         int cbp_index;
+        int ret;
         w->j_type = 0;
 
-        parse_mb_skip(w);
+        ret = parse_mb_skip(w);
+        if (ret < 0)
+            return ret;
         cbp_index = decode012(&s->gb);
         w->cbp_table_index = wmv2_get_cbp_table_index(s, cbp_index);
 
@@ -359,6 +369,8 @@ int ff_wmv2_decode_mb(MpegEncContext *s, int16_t block[6][64])
             w->hshift      = 0;
             return 0;
         }
+        if (get_bits_left(&s->gb) <= 0)
+            return AVERROR_INVALIDDATA;
 
         code = get_vlc2(&s->gb, ff_mb_non_intra_vlc[w->cbp_table_index].table,
                         MB_NON_INTRA_VLC_BITS, 3);
@@ -369,6 +381,8 @@ int ff_wmv2_decode_mb(MpegEncContext *s, int16_t block[6][64])
         cbp = code & 0x3f;
     } else {
         s->mb_intra = 1;
+        if (get_bits_left(&s->gb) <= 0)
+            return AVERROR_INVALIDDATA;
         code = get_vlc2(&s->gb, ff_msmp4_mb_i_vlc.table, MB_INTRA_VLC_BITS, 2);
         if (code < 0) {
             av_log(s->avctx, AV_LOG_ERROR,