Code: static int g2m_init_buffers(G2MContext *c)
{
     int aligned_height;
 
     if (!c->framebuf || c->old_width < c->width || c->old_height < c->height) {
        c->framebuf_stride = FFALIGN(c->width * 3, 16);
        aligned_height     = FFALIGN(c->height,    16);
         av_free(c->framebuf);
         c->framebuf = av_mallocz(c->framebuf_stride * aligned_height);
         if (!c->framebuf)
            return AVERROR(ENOMEM);
    }
    if (!c->synth_tile || !c->jpeg_tile ||
        c->old_tile_w < c->tile_width ||
        c->old_tile_h < c->tile_height) {
        c->tile_stride = FFALIGN(c->tile_width, 16) * 3;
        aligned_height = FFALIGN(c->tile_height,    16);
        av_free(c->synth_tile);
        av_free(c->jpeg_tile);
        av_free(c->kempf_buf);
        av_free(c->kempf_flags);
        c->synth_tile  = av_mallocz(c->tile_stride      * aligned_height);
        c->jpeg_tile   = av_mallocz(c->tile_stride      * aligned_height);
        c->kempf_buf   = av_mallocz((c->tile_width + 1) * aligned_height
                                    + FF_INPUT_BUFFER_PADDING_SIZE);
        c->kempf_flags = av_mallocz( c->tile_width      * aligned_height);
        if (!c->synth_tile || !c->jpeg_tile ||
            !c->kempf_buf || !c->kempf_flags)
            return AVERROR(ENOMEM);
    }

    return 0;
}

Vulnerability Type: DoS Overflow 
CWE ID: CWE-119
Summary: The g2m_init_buffers function in libavcodec/g2meet.c in FFmpeg before 2.1 does not properly allocate memory for tiles, which allows remote attackers to cause a denial of service (out-of-bounds array access) or possibly have unspecified other impact via crafted Go2Webinar data.
Commit Message: avcodec/g2meet: Fix framebuf size

Currently the code can in some cases draw tiles that hang outside the
allocated buffer. This patch increases the buffer size to avoid out
of array accesses. An alternative would be to fail if such tiles are
encountered.
I do not know if any valid files use such hanging tiles.

Fixes Ticket2971
Found-by: ami_stuff
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>