Commit message: Do not attempt to decode APE file with no frames

This fixes invalid reads/writes with this sample:
http://packetstorm.linuxsecurity.com/1103-exploits/vlc105-dos.txt
CVE: CVE-2011-2161
CWE: CWE-399
Vulnerability description: The ape_read_header function in ape.c in libavformat in FFmpeg before 0.5.4, as used in MPlayer, VideoLAN VLC media player, and other products, allows remote attackers to cause a denial of service (application crash) via an APE (aka Monkey's Audio) file that contains a header but no frames.

Project: FFmpeg
File: ape.c

static int ape_read_header(AVFormatContext * s, AVFormatParameters * ap)
{
    AVIOContext *pb = s->pb;
    APEContext *ape = s->priv_data;
    AVStream *st;
    uint32_t tag;
    int i;
    int total_blocks;
    int64_t pts;

    /* TODO: Skip any leading junk such as id3v2 tags */
    ape->junklength = 0;

    tag = avio_rl32(pb);
    if (tag != MKTAG('M', 'A', 'C', ' '))
        return -1;

    ape->fileversion = avio_rl16(pb);

    if (ape->fileversion < APE_MIN_VERSION || ape->fileversion > APE_MAX_VERSION) {
        av_log(s, AV_LOG_ERROR, "Unsupported file version - %d.%02d\n", ape->fileversion / 1000, (ape->fileversion % 1000) / 10);
        return -1;
    }

    if (ape->fileversion >= 3980) {
        ape->padding1             = avio_rl16(pb);
        ape->descriptorlength     = avio_rl32(pb);
        ape->headerlength         = avio_rl32(pb);
        ape->seektablelength      = avio_rl32(pb);
        ape->wavheaderlength      = avio_rl32(pb);
        ape->audiodatalength      = avio_rl32(pb);
        ape->audiodatalength_high = avio_rl32(pb);
        ape->wavtaillength        = avio_rl32(pb);
        avio_read(pb, ape->md5, 16);

        /* Skip any unknown bytes at the end of the descriptor.
           This is for future compatibility */
        if (ape->descriptorlength > 52)
            avio_seek(pb, ape->descriptorlength - 52, SEEK_CUR);

        /* Read header data */
        ape->compressiontype      = avio_rl16(pb);
        ape->formatflags          = avio_rl16(pb);
        ape->blocksperframe       = avio_rl32(pb);
        ape->finalframeblocks     = avio_rl32(pb);
        ape->totalframes          = avio_rl32(pb);
        ape->bps                  = avio_rl16(pb);
        ape->channels             = avio_rl16(pb);
        ape->samplerate           = avio_rl32(pb);
    } else {
        ape->descriptorlength = 0;
        ape->headerlength = 32;

        ape->compressiontype      = avio_rl16(pb);
        ape->formatflags          = avio_rl16(pb);
        ape->channels             = avio_rl16(pb);
        ape->samplerate           = avio_rl32(pb);
        ape->wavheaderlength      = avio_rl32(pb);
        ape->wavtaillength        = avio_rl32(pb);
        ape->totalframes          = avio_rl32(pb);
        ape->finalframeblocks     = avio_rl32(pb);

        if (ape->formatflags & MAC_FORMAT_FLAG_HAS_PEAK_LEVEL) {
            avio_seek(pb, 4, SEEK_CUR); /* Skip the peak level */
            ape->headerlength += 4;
        }

        if (ape->formatflags & MAC_FORMAT_FLAG_HAS_SEEK_ELEMENTS) {
            ape->seektablelength = avio_rl32(pb);
            ape->headerlength += 4;
            ape->seektablelength *= sizeof(int32_t);
        } else
            ape->seektablelength = ape->totalframes * sizeof(int32_t);

        if (ape->formatflags & MAC_FORMAT_FLAG_8_BIT)
            ape->bps = 8;
        else if (ape->formatflags & MAC_FORMAT_FLAG_24_BIT)
            ape->bps = 24;
        else
            ape->bps = 16;

        if (ape->fileversion >= 3950)
            ape->blocksperframe = 73728 * 4;
        else if (ape->fileversion >= 3900 || (ape->fileversion >= 3800  && ape->compressiontype >= 4000))
            ape->blocksperframe = 73728;
        else
            ape->blocksperframe = 9216;

        /* Skip any stored wav header */
        if (!(ape->formatflags & MAC_FORMAT_FLAG_CREATE_WAV_HEADER))
             avio_seek(pb, ape->wavheaderlength, SEEK_CUR);
     }
 
     if(ape->totalframes > UINT_MAX / sizeof(APEFrame)){
         av_log(s, AV_LOG_ERROR, "Too many frames: %d\n", ape->totalframes);
         return -1;
    }
    ape->frames       = av_malloc(ape->totalframes * sizeof(APEFrame));
    if(!ape->frames)
        return AVERROR(ENOMEM);
    ape->firstframe   = ape->junklength + ape->descriptorlength + ape->headerlength + ape->seektablelength + ape->wavheaderlength;
    ape->currentframe = 0;


    ape->totalsamples = ape->finalframeblocks;
    if (ape->totalframes > 1)
        ape->totalsamples += ape->blocksperframe * (ape->totalframes - 1);

    if (ape->seektablelength > 0) {
        ape->seektable = av_malloc(ape->seektablelength);
        for (i = 0; i < ape->seektablelength / sizeof(uint32_t); i++)
            ape->seektable[i] = avio_rl32(pb);
    }

    ape->frames[0].pos     = ape->firstframe;
    ape->frames[0].nblocks = ape->blocksperframe;
    ape->frames[0].skip    = 0;
    for (i = 1; i < ape->totalframes; i++) {
        ape->frames[i].pos      = ape->seektable[i]; //ape->frames[i-1].pos + ape->blocksperframe;
        ape->frames[i].nblocks  = ape->blocksperframe;
        ape->frames[i - 1].size = ape->frames[i].pos - ape->frames[i - 1].pos;
        ape->frames[i].skip     = (ape->frames[i].pos - ape->frames[0].pos) & 3;
    }
    ape->frames[ape->totalframes - 1].size    = ape->finalframeblocks * 4;
    ape->frames[ape->totalframes - 1].nblocks = ape->finalframeblocks;

    for (i = 0; i < ape->totalframes; i++) {
        if(ape->frames[i].skip){
            ape->frames[i].pos  -= ape->frames[i].skip;
            ape->frames[i].size += ape->frames[i].skip;
        }
        ape->frames[i].size = (ape->frames[i].size + 3) & ~3;
    }


    ape_dumpinfo(s, ape);

    /* try to read APE tags */
    if (!url_is_streamed(pb)) {
        ff_ape_parse_tag(s);
        avio_seek(pb, 0, SEEK_SET);
    }

    av_log(s, AV_LOG_DEBUG, "Decoding file - v%d.%02d, compression level %d\n", ape->fileversion / 1000, (ape->fileversion % 1000) / 10, ape->compressiontype);

    /* now we are ready: build format streams */
    st = av_new_stream(s, 0);
    if (!st)
        return -1;

    total_blocks = (ape->totalframes == 0) ? 0 : ((ape->totalframes - 1) * ape->blocksperframe) + ape->finalframeblocks;

    st->codec->codec_type      = AVMEDIA_TYPE_AUDIO;
    st->codec->codec_id        = CODEC_ID_APE;
    st->codec->codec_tag       = MKTAG('A', 'P', 'E', ' ');
    st->codec->channels        = ape->channels;
    st->codec->sample_rate     = ape->samplerate;
    st->codec->bits_per_coded_sample = ape->bps;
    st->codec->frame_size      = MAC_SUBFRAME_SIZE;

    st->nb_frames = ape->totalframes;
    st->start_time = 0;
    st->duration  = total_blocks / MAC_SUBFRAME_SIZE;
    av_set_pts_info(st, 64, MAC_SUBFRAME_SIZE, ape->samplerate);

    st->codec->extradata = av_malloc(APE_EXTRADATA_SIZE);
    st->codec->extradata_size = APE_EXTRADATA_SIZE;
    AV_WL16(st->codec->extradata + 0, ape->fileversion);
    AV_WL16(st->codec->extradata + 2, ape->compressiontype);
    AV_WL16(st->codec->extradata + 4, ape->formatflags);

    pts = 0;
    for (i = 0; i < ape->totalframes; i++) {
        ape->frames[i].pts = pts;
        av_add_index_entry(st, ape->frames[i].pos, ape->frames[i].pts, 0, 0, AVINDEX_KEYFRAME);
        pts += ape->blocksperframe / MAC_SUBFRAME_SIZE;
    }

    return 0;
}