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grub2/SOURCES/0435-video-readers-jpeg-Cat...

45 lines
1.5 KiB

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Daniel Axtens <dja@axtens.net>
Date: Fri, 15 Jan 2021 13:29:53 +1100
Subject: [PATCH] video/readers/jpeg: Catch OOB reads/writes in
grub_jpeg_decode_du()
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>
---
grub-core/video/readers/jpeg.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/grub-core/video/readers/jpeg.c b/grub-core/video/readers/jpeg.c
index 23f919aa0..e5148120f 100644
--- a/grub-core/video/readers/jpeg.c
+++ b/grub-core/video/readers/jpeg.c
@@ -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++;
}