Code: static int mv_read_header(AVFormatContext *avctx)
{
    MvContext *mv = avctx->priv_data;
    AVIOContext *pb = avctx->pb;
    AVStream *ast = NULL, *vst = NULL; //initialization to suppress warning
    int version, i;
    int ret;

    avio_skip(pb, 4);

    version = avio_rb16(pb);
    if (version == 2) {
        uint64_t timestamp;
        int v;
        avio_skip(pb, 22);

        /* allocate audio track first to prevent unnecessary seeking
         * (audio packet always precede video packet for a given frame) */
        ast = avformat_new_stream(avctx, NULL);
        if (!ast)
            return AVERROR(ENOMEM);

        vst = avformat_new_stream(avctx, NULL);
        if (!vst)
            return AVERROR(ENOMEM);
        avpriv_set_pts_info(vst, 64, 1, 15);
        vst->codecpar->codec_type = AVMEDIA_TYPE_VIDEO;
        vst->avg_frame_rate    = av_inv_q(vst->time_base);
        vst->nb_frames         = avio_rb32(pb);
        v = avio_rb32(pb);
        switch (v) {
        case 1:
            vst->codecpar->codec_id = AV_CODEC_ID_MVC1;
            break;
        case 2:
            vst->codecpar->format = AV_PIX_FMT_ARGB;
            vst->codecpar->codec_id = AV_CODEC_ID_RAWVIDEO;
            break;
        default:
            avpriv_request_sample(avctx, "Video compression %i", v);
            break;
        }
        vst->codecpar->codec_tag = 0;
        vst->codecpar->width     = avio_rb32(pb);
        vst->codecpar->height    = avio_rb32(pb);
        avio_skip(pb, 12);

        ast->codecpar->codec_type  = AVMEDIA_TYPE_AUDIO;
        ast->nb_frames          = vst->nb_frames;
        ast->codecpar->sample_rate = avio_rb32(pb);
        if (ast->codecpar->sample_rate <= 0) {
            av_log(avctx, AV_LOG_ERROR, "Invalid sample rate %d\n", ast->codecpar->sample_rate);
            return AVERROR_INVALIDDATA;
        }
        avpriv_set_pts_info(ast, 33, 1, ast->codecpar->sample_rate);
        if (set_channels(avctx, ast, avio_rb32(pb)) < 0)
            return AVERROR_INVALIDDATA;

        v = avio_rb32(pb);
        if (v == AUDIO_FORMAT_SIGNED) {
            ast->codecpar->codec_id = AV_CODEC_ID_PCM_S16BE;
        } else {
            avpriv_request_sample(avctx, "Audio compression (format %i)", v);
        }

        avio_skip(pb, 12);
        var_read_metadata(avctx, "title", 0x80);
        var_read_metadata(avctx, "comment", 0x100);
        avio_skip(pb, 0x80);

        timestamp = 0;
        for (i = 0; i < vst->nb_frames; i++) {
             uint32_t pos   = avio_rb32(pb);
             uint32_t asize = avio_rb32(pb);
             uint32_t vsize = avio_rb32(pb);
             avio_skip(pb, 8);
             av_add_index_entry(ast, pos, timestamp, asize, 0, AVINDEX_KEYFRAME);
             av_add_index_entry(vst, pos + asize, i, vsize, 0, AVINDEX_KEYFRAME);
            timestamp += asize / (ast->codecpar->channels * 2);
        }
    } else if (!version && avio_rb16(pb) == 3) {
        avio_skip(pb, 4);

        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");
            return AVERROR_PATCHWELCOME;
        } else if (mv->nb_audio_tracks) {
            ast = avformat_new_stream(avctx, NULL);
            if (!ast)
                return AVERROR(ENOMEM);
            ast->codecpar->codec_type = AVMEDIA_TYPE_AUDIO;
            if ((read_table(avctx, ast, parse_audio_var)) < 0)
                return ret;
            if (mv->acompression == 100 &&
                mv->aformat == AUDIO_FORMAT_SIGNED &&
                ast->codecpar->bits_per_coded_sample == 16) {
                ast->codecpar->codec_id = AV_CODEC_ID_PCM_S16BE;
            } else {
                avpriv_request_sample(avctx,
                                      "Audio compression %i (format %i, sr %i)",
                                      mv->acompression, mv->aformat,
                                      ast->codecpar->bits_per_coded_sample);
                ast->codecpar->codec_id = AV_CODEC_ID_NONE;
            }
            if (ast->codecpar->channels <= 0) {
                av_log(avctx, AV_LOG_ERROR, "No valid channel count found.\n");
                return AVERROR_INVALIDDATA;
            }
        }

        if (mv->nb_video_tracks > 1) {
            avpriv_request_sample(avctx, "Multiple video streams support");
            return AVERROR_PATCHWELCOME;
        } else if (mv->nb_video_tracks) {
            vst = avformat_new_stream(avctx, NULL);
            if (!vst)
                return AVERROR(ENOMEM);
            vst->codecpar->codec_type = AVMEDIA_TYPE_VIDEO;
            if ((ret = read_table(avctx, vst, parse_video_var))<0)
                return ret;
        }

        if (mv->nb_audio_tracks)
            read_index(pb, ast);

        if (mv->nb_video_tracks)
            read_index(pb, vst);
    } else {
        avpriv_request_sample(avctx, "Version %i", version);
        return AVERROR_PATCHWELCOME;
    }

    return 0;
}

Vulnerability Type: 
CWE ID: CWE-834
Summary: In libavformat/mvdec.c in FFmpeg 3.3.3, a DoS in mv_read_header() due to lack of an EOF (End of File) check might cause huge CPU and memory consumption. When a crafted MV file, which claims a large *nb_frames* field in the header but does not contain sufficient backing data, is provided, the loop over the frames would consume huge CPU and memory resources, since there is no EOF check inside the loop.
Commit Message: avformat/mvdec: Fix DoS due to lack of eof check

Fixes: loop.mv

Found-by: Xiaohei and Wangchu from Alibaba Security Team
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>