avcodec/truemotion2: Check huffman code max bits

Fixes: Timeout
Fixes: 10984/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_TRUEMOTION2_fuzzer-6643310750859264

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

libavcodec/truemotion2.c

@@ -112,9 +112,13 @@ typedef struct TM2Huff {
     int *lens; ///< codelengths
 } TM2Huff;
 
+/**
+ *
+ * @returns the length of the longest code or an AVERROR code
+ */
 static int tm2_read_tree(TM2Context *ctx, uint32_t prefix, int length, TM2Huff *huff)
 {
-    int ret;
+    int ret, ret2;
     if (length > huff->max_bits) {
         av_log(ctx->avctx, AV_LOG_ERROR, "Tree exceeded its given depth (%i)\n",
                huff->max_bits);
@@ -133,14 +137,14 @@ static int tm2_read_tree(TM2Context *ctx, uint32_t prefix, int length, TM2Huff *
         huff->bits[huff->num] = prefix;
         huff->lens[huff->num] = length;
         huff->num++;
-        return 0;
+        return length;
     } else { /* non-terminal node */
-        if ((ret = tm2_read_tree(ctx, prefix << 1, length + 1, huff)) < 0)
-            return ret;
+        if ((ret2 = tm2_read_tree(ctx, prefix << 1, length + 1, huff)) < 0)
+            return ret2;
         if ((ret = tm2_read_tree(ctx, (prefix << 1) | 1, length + 1, huff)) < 0)
             return ret;
     }
-    return 0;
+    return FFMAX(ret, ret2);
 }
 
 static int tm2_build_huff_table(TM2Context *ctx, TM2Codes *code)
@@ -183,6 +187,11 @@ static int tm2_build_huff_table(TM2Context *ctx, TM2Codes *code)
 
     res = tm2_read_tree(ctx, 0, 0, &huff);
 
+    if (res >= 0 && res != huff.max_bits) {
+        av_log(ctx->avctx, AV_LOG_ERROR, "Got less bits than expected: %i of %i\n",
+               res, huff.max_bits);
+        res = AVERROR_INVALIDDATA;
+    }
     if (huff.num != huff.max_num) {
         av_log(ctx->avctx, AV_LOG_ERROR, "Got less codes than expected: %i of %i\n",
                huff.num, huff.max_num);