The key line is:
du[jpeg_zigzag_order[pos]] = val * (int) data->quan_table[qt][pos];
jpeg_zigzag_order is grub_uint8_t[64].
I don't understand JPEG decoders quite well enough to explain what's
going on here. However, I observe sometimes pos=64, which leads to an
OOB read of the jpeg_zigzag_order global then an OOB write to du.
That leads to various unpleasant memory corruption conditions.
Catch where pos >= ARRAY_SIZE(jpeg_zigzag_order) and bail.
Signed-off-by: Daniel Axtens <dja@axtens.net>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
34b85a6e07