avformat/mvdec: Check size in read_table() for validity

This check is redundant with the previous commit but it provides
better error messages and feedback while the previous commit
ensures that var_read_string() doesnt return uninitialized arrays
if it itself is feeded with an invalid size possibly through a
different future codepath.

Fixes: asan_heap-oob_49b1e5_12_011.movie
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/mvdec.c

@@ -223,7 +223,7 @@ static int parse_video_var(AVFormatContext *avctx, AVStream *st,
     return 0;
 }
 
-static void read_table(AVFormatContext *avctx, AVStream *st,
+static int read_table(AVFormatContext *avctx, AVStream *st,
                        int (*parse)(AVFormatContext *avctx, AVStream *st,
                                     const char *name, int size))
 {
@@ -238,11 +238,16 @@ static void read_table(AVFormatContext *avctx, AVStream *st,
         avio_read(pb, name, 16);
         name[sizeof(name) - 1] = 0;
         size = avio_rb32(pb);
+        if (size < 0) {
+            av_log(avctx, AV_LOG_ERROR, "entry size %d is invalid\n", size);
+            return AVERROR_INVALIDDATA;
+        }
         if (parse(avctx, st, name, size) < 0) {
             avpriv_request_sample(avctx, "Variable %s", name);
             avio_skip(pb, size);
         }
     }
+    return 0;
 }
 
 static void read_index(AVIOContext *pb, AVStream *st)
@@ -268,6 +273,7 @@ static int mv_read_header(AVFormatContext *avctx)
     AVIOContext *pb = avctx->pb;
     AVStream *ast = NULL, *vst = NULL; //initialization to suppress warning
     int version, i;
+    int ret;
 
     avio_skip(pb, 4);
 
@@ -340,7 +346,8 @@ static int mv_read_header(AVFormatContext *avctx)
     } else if (!version && avio_rb16(pb) == 3) {
         avio_skip(pb, 4);
 
-        read_table(avctx, NULL, parse_global_var);
+        if ((ret = read_table(avctx, NULL, parse_global_var)) < 0)
+            return ret;
 
         if (mv->nb_audio_tracks > 1) {
             avpriv_request_sample(avctx, "Multiple audio streams support");
@@ -350,7 +357,8 @@ static int mv_read_header(AVFormatContext *avctx)
             if (!ast)
                 return AVERROR(ENOMEM);
             ast->codec->codec_type = AVMEDIA_TYPE_AUDIO;
-            read_table(avctx, ast, parse_audio_var);
+            if ((read_table(avctx, ast, parse_audio_var)) < 0)
+                return ret;
             if (mv->acompression == 100 &&
                 mv->aformat == AUDIO_FORMAT_SIGNED &&
                 ast->codec->bits_per_coded_sample == 16) {
@@ -376,7 +384,8 @@ static int mv_read_header(AVFormatContext *avctx)
             if (!vst)
                 return AVERROR(ENOMEM);
             vst->codec->codec_type = AVMEDIA_TYPE_VIDEO;
-            read_table(avctx, vst, parse_video_var);
+            if ((ret = read_table(avctx, vst, parse_video_var))<0)
+                return ret;
         }
 
         if (mv->nb_audio_tracks)