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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Daniel Axtens <dja@axtens.net>
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Date: Fri, 15 Jan 2021 13:29:53 +1100
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Subject: [PATCH] video/readers/jpeg: Catch OOB reads/writes in
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grub_jpeg_decode_du()
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The key line is:
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du[jpeg_zigzag_order[pos]] = val * (int) data->quan_table[qt][pos];
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jpeg_zigzag_order is grub_uint8_t[64].
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I don't understand JPEG decoders quite well enough to explain what's
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going on here. However, I observe sometimes pos=64, which leads to an
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OOB read of the jpeg_zigzag_order global then an OOB write to du.
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That leads to various unpleasant memory corruption conditions.
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Catch where pos >= ARRAY_SIZE(jpeg_zigzag_order) and bail.
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Signed-off-by: Daniel Axtens <dja@axtens.net>
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Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
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---
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grub-core/video/readers/jpeg.c | 8 ++++++++
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1 file changed, 8 insertions(+)
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diff --git a/grub-core/video/readers/jpeg.c b/grub-core/video/readers/jpeg.c
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index 23f919aa0..e5148120f 100644
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--- a/grub-core/video/readers/jpeg.c
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+++ b/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)
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val = grub_jpeg_get_number (data, num & 0xF);
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num >>= 4;
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pos += num;
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+
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+ if (pos >= ARRAY_SIZE (jpeg_zigzag_order))
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+ {
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+ grub_error (GRUB_ERR_BAD_FILE_TYPE,
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+ "jpeg: invalid position in zigzag order!?");
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+ return;
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+ }
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+
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du[jpeg_zigzag_order[pos]] = val * (int) data->quan_table[qt][pos];
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pos++;
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}
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