forked from pool/grub2
78 lines
2.5 KiB
Diff
78 lines
2.5 KiB
Diff
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From 9a6e9ad21eb2f414dce6eaedd41e146a28142101 Mon Sep 17 00:00:00 2001
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From: Daniel Axtens <dja@axtens.net>
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Date: Wed, 7 Jul 2021 15:38:19 +1000
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Subject: [PATCH 15/32] video/readers/jpeg: Block int underflow -> wild pointer
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write
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Certain 1 px wide images caused a wild pointer write in
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grub_jpeg_ycrcb_to_rgb(). This was caused because in grub_jpeg_decode_data(),
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we have the following loop:
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for (; data->r1 < nr1 && (!data->dri || rst);
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data->r1++, data->bitmap_ptr += (vb * data->image_width - hb * nc1) * 3)
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We did not check if vb * width >= hb * nc1.
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On a 64-bit platform, if that turns out to be negative, it will underflow,
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be interpreted as unsigned 64-bit, then be added to the 64-bit pointer, so
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we see data->bitmap_ptr jump, e.g.:
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0x6180_0000_0480 to
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0x6181_0000_0498
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^
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~--- carry has occurred and this pointer is now far away from
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any object.
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On a 32-bit platform, it will decrement the pointer, creating a pointer
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that won't crash but will overwrite random data.
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Catch the underflow and error out.
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Fixes: CVE-2021-3697
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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 | 10 +++++++++-
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1 file changed, 9 insertions(+), 1 deletion(-)
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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 1df1171d78..97a533b24f 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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@@ -23,6 +23,7 @@
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#include <grub/mm.h>
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#include <grub/misc.h>
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#include <grub/bufio.h>
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+#include <grub/safemath.h>
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GRUB_MOD_LICENSE ("GPLv3+");
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@@ -693,6 +694,7 @@ static grub_err_t
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grub_jpeg_decode_data (struct grub_jpeg_data *data)
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{
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unsigned c1, vb, hb, nr1, nc1;
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+ unsigned stride_a, stride_b, stride;
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int rst = data->dri;
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grub_err_t err = GRUB_ERR_NONE;
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@@ -705,8 +707,14 @@ grub_jpeg_decode_data (struct grub_jpeg_data *data)
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return grub_error (GRUB_ERR_BAD_FILE_TYPE,
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"jpeg: attempted to decode data before start of stream");
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+ if (grub_mul(vb, data->image_width, &stride_a) ||
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+ grub_mul(hb, nc1, &stride_b) ||
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+ grub_sub(stride_a, stride_b, &stride))
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+ return grub_error (GRUB_ERR_BAD_FILE_TYPE,
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+ "jpeg: cannot decode image with these dimensions");
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+
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for (; data->r1 < nr1 && (!data->dri || rst);
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- data->r1++, data->bitmap_ptr += (vb * data->image_width - hb * nc1) * 3)
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+ data->r1++, data->bitmap_ptr += stride * 3)
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for (c1 = 0; c1 < nc1 && (!data->dri || rst);
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c1++, rst--, data->bitmap_ptr += hb * 3)
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{
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--
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2.34.1
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