avcodec/mpeg4video: Check time_incr

Fixes assertion failure
Fixes out of memory access

Fixes: test_casex.ivf
Found-by: Tyson Smith <twsmith@mozilla.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/mpeg4video.h

@@ -140,7 +140,7 @@ void ff_mpeg4_encode_mb(MpegEncContext *s,
 void ff_mpeg4_pred_ac(MpegEncContext *s, int16_t *block, int n,
                       int dir);
 void ff_set_mpeg4_time(MpegEncContext *s);
-void ff_mpeg4_encode_picture_header(MpegEncContext *s, int picture_number);
+int ff_mpeg4_encode_picture_header(MpegEncContext *s, int picture_number);
 
 int ff_mpeg4_decode_picture_header(Mpeg4DecContext *ctx, GetBitContext *gb);
 void ff_mpeg4_encode_video_packet_header(MpegEncContext *s);

libavcodec/mpeg4videoenc.c

@@ -1086,7 +1086,7 @@ static void mpeg4_encode_vol_header(MpegEncContext *s,
 }
 
 /* write mpeg4 VOP header */
-void ff_mpeg4_encode_picture_header(MpegEncContext *s, int picture_number)
+int ff_mpeg4_encode_picture_header(MpegEncContext *s, int picture_number)
 {
     int time_incr;
     int time_div, time_mod;
@@ -1112,6 +1112,12 @@ void ff_mpeg4_encode_picture_header(MpegEncContext *s, int picture_number)
     time_mod  = FFUMOD(s->time, s->avctx->time_base.den);
     time_incr = time_div - s->last_time_base;
     av_assert0(time_incr >= 0);
+
+    // This limits the frame duration to max 1 hour
+    if (time_incr > 3600) {
+        av_log(s->avctx, AV_LOG_ERROR, "time_incr %d too large\n", time_incr);
+        return AVERROR(EINVAL);
+    }
     while (time_incr--)
         put_bits(&s->pb, 1, 1);
 
@@ -1137,6 +1143,8 @@ void ff_mpeg4_encode_picture_header(MpegEncContext *s, int picture_number)
         put_bits(&s->pb, 3, s->f_code);  /* fcode_for */
     if (s->pict_type == AV_PICTURE_TYPE_B)
         put_bits(&s->pb, 3, s->b_code);  /* fcode_back */
+
+    return 0;
 }
 
 static av_cold void init_uni_dc_tab(void)

libavcodec/mpegvideo_enc.c

@@ -3836,9 +3836,11 @@ static int encode_picture(MpegEncContext *s, int picture_number)
             ff_wmv2_encode_picture_header(s, picture_number);
         else if (CONFIG_MSMPEG4_ENCODER && s->msmpeg4_version)
             ff_msmpeg4_encode_picture_header(s, picture_number);
-        else if (CONFIG_MPEG4_ENCODER && s->h263_pred)
-            ff_mpeg4_encode_picture_header(s, picture_number);
-        else if (CONFIG_RV10_ENCODER && s->codec_id == AV_CODEC_ID_RV10) {
+        else if (CONFIG_MPEG4_ENCODER && s->h263_pred) {
+            ret = ff_mpeg4_encode_picture_header(s, picture_number);
+            if (ret < 0)
+                return ret;
+        } else if (CONFIG_RV10_ENCODER && s->codec_id == AV_CODEC_ID_RV10) {
             ret = ff_rv10_encode_picture_header(s, picture_number);
             if (ret < 0)
                 return ret;