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video/readers/jpeg: Catch OOB reads/writes in grub_jpeg_decode_du()

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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>
This commit is contained in:
Daniel Axtens 2021-01-15 13:29:53 +11:00 committed by Daniel Kiper
parent 693989598f
commit 34b85a6e07
1 changed files with 8 additions and 0 deletions
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8
grub-core/video/readers/jpeg.c
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@ -526,6 +526,14 @@ grub_jpeg_decode_du (struct grub_jpeg_data *data, int id, jpeg_data_unit_t du)
val = grub_jpeg_get_number (data, num & 0xF);
num >>= 4;
pos += num;
if (pos >= ARRAY_SIZE (jpeg_zigzag_order))
{
grub_error (GRUB_ERR_BAD_FILE_TYPE,
"jpeg: invalid position in zigzag order!?");
return;
}
du[jpeg_zigzag_order[pos]] = val * (int) data->quan_table[qt][pos];
pos++;
}