Code: static int get_siz(Jpeg2000DecoderContext *s)
{
    int i;
    int ncomponents;
    uint32_t log2_chroma_wh = 0;
    const enum AVPixelFormat *possible_fmts = NULL;
    int possible_fmts_nb = 0;

    if (bytestream2_get_bytes_left(&s->g) < 36)
        return AVERROR_INVALIDDATA;

    s->avctx->profile = bytestream2_get_be16u(&s->g); // Rsiz
    s->width          = bytestream2_get_be32u(&s->g); // Width
    s->height         = bytestream2_get_be32u(&s->g); // Height
    s->image_offset_x = bytestream2_get_be32u(&s->g); // X0Siz
    s->image_offset_y = bytestream2_get_be32u(&s->g); // Y0Siz
    s->tile_width     = bytestream2_get_be32u(&s->g); // XTSiz
    s->tile_height    = bytestream2_get_be32u(&s->g); // YTSiz
    s->tile_offset_x  = bytestream2_get_be32u(&s->g); // XT0Siz
    s->tile_offset_y  = bytestream2_get_be32u(&s->g); // YT0Siz
    ncomponents       = bytestream2_get_be16u(&s->g); // CSiz

    if (ncomponents <= 0) {
        av_log(s->avctx, AV_LOG_ERROR, "Invalid number of components: %d\n",
               s->ncomponents);
        return AVERROR_INVALIDDATA;
    }

    if (ncomponents > 4) {
        avpriv_request_sample(s->avctx, "Support for %d components",
                              s->ncomponents);
        return AVERROR_PATCHWELCOME;
    }

    s->ncomponents = ncomponents;

    if (s->tile_width <= 0 || s->tile_height <= 0) {
        av_log(s->avctx, AV_LOG_ERROR, "Invalid tile dimension %dx%d.\n",
               s->tile_width, s->tile_height);
        return AVERROR_INVALIDDATA;
    }

    if (bytestream2_get_bytes_left(&s->g) < 3 * s->ncomponents)
        return AVERROR_INVALIDDATA;

    for (i = 0; i < s->ncomponents; i++) { // Ssiz_i XRsiz_i, YRsiz_i
        uint8_t x    = bytestream2_get_byteu(&s->g);
        s->cbps[i]   = (x & 0x7f) + 1;
        s->precision = FFMAX(s->cbps[i], s->precision);
         s->sgnd[i]   = !!(x & 0x80);
         s->cdx[i]    = bytestream2_get_byteu(&s->g);
         s->cdy[i]    = bytestream2_get_byteu(&s->g);
        if (!s->cdx[i] || !s->cdy[i]) {
             av_log(s->avctx, AV_LOG_ERROR, "Invalid sample seperation\n");
             return AVERROR_INVALIDDATA;
         }
        log2_chroma_wh |= s->cdy[i] >> 1 << i * 4 | s->cdx[i] >> 1 << i * 4 + 2;
    }

    s->numXtiles = ff_jpeg2000_ceildiv(s->width  - s->tile_offset_x, s->tile_width);
    s->numYtiles = ff_jpeg2000_ceildiv(s->height - s->tile_offset_y, s->tile_height);

    if (s->numXtiles * (uint64_t)s->numYtiles > INT_MAX/sizeof(*s->tile)) {
        s->numXtiles = s->numYtiles = 0;
        return AVERROR(EINVAL);
    }

    s->tile = av_mallocz_array(s->numXtiles * s->numYtiles, sizeof(*s->tile));
    if (!s->tile) {
        s->numXtiles = s->numYtiles = 0;
        return AVERROR(ENOMEM);
    }

    for (i = 0; i < s->numXtiles * s->numYtiles; i++) {
        Jpeg2000Tile *tile = s->tile + i;

        tile->comp = av_mallocz(s->ncomponents * sizeof(*tile->comp));
        if (!tile->comp)
            return AVERROR(ENOMEM);
    }

    /* compute image size with reduction factor */
    s->avctx->width  = ff_jpeg2000_ceildivpow2(s->width  - s->image_offset_x,
                                               s->reduction_factor);
    s->avctx->height = ff_jpeg2000_ceildivpow2(s->height - s->image_offset_y,
                                               s->reduction_factor);

    if (s->avctx->profile == FF_PROFILE_JPEG2000_DCINEMA_2K ||
        s->avctx->profile == FF_PROFILE_JPEG2000_DCINEMA_4K) {
        possible_fmts = xyz_pix_fmts;
        possible_fmts_nb = FF_ARRAY_ELEMS(xyz_pix_fmts);
    } else {
        switch (s->colour_space) {
        case 16:
            possible_fmts = rgb_pix_fmts;
            possible_fmts_nb = FF_ARRAY_ELEMS(rgb_pix_fmts);
            break;
        case 17:
            possible_fmts = gray_pix_fmts;
            possible_fmts_nb = FF_ARRAY_ELEMS(gray_pix_fmts);
            break;
        case 18:
            possible_fmts = yuv_pix_fmts;
            possible_fmts_nb = FF_ARRAY_ELEMS(yuv_pix_fmts);
            break;
        default:
            possible_fmts = all_pix_fmts;
            possible_fmts_nb = FF_ARRAY_ELEMS(all_pix_fmts);
            break;
        }
    }
    for (i = 0; i < possible_fmts_nb; ++i) {
        if (pix_fmt_match(possible_fmts[i], ncomponents, s->precision, log2_chroma_wh, s->pal8)) {
            s->avctx->pix_fmt = possible_fmts[i];
            break;
        }
    }
    if (s->avctx->pix_fmt == AV_PIX_FMT_NONE) {
        av_log(s->avctx, AV_LOG_ERROR,
               "Unknown pix_fmt, profile: %d, colour_space: %d, "
               "components: %d, precision: %d, "
               "cdx[1]: %d, cdy[1]: %d, cdx[2]: %d, cdy[2]: %d\n",
               s->avctx->profile, s->colour_space, ncomponents, s->precision,
               ncomponents > 2 ? s->cdx[1] : 0,
               ncomponents > 2 ? s->cdy[1] : 0,
               ncomponents > 2 ? s->cdx[2] : 0,
               ncomponents > 2 ? s->cdy[2] : 0);
    }
    return 0;
}

Vulnerability Type: DoS Overflow 
CWE ID: CWE-119
Summary: The get_siz function in libavcodec/jpeg2000dec.c in FFmpeg before 2.1 does not ensure the expected sample separation, which allows remote attackers to cause a denial of service (out-of-bounds array access) or possibly have unspecified other impact via crafted JPEG2000 data.
Commit Message: avcodec/jpeg2000dec: Check cdx/y values more carefully

Some invalid values where not handled correctly in the later pixel
format matching code.
Fixes out of array accesses
Fixes Ticket2848

Found-by: Piotr Bandurski <ami_stuff@o2.pl>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>