poky/meta/recipes-bsp/grub/files/CVE-2021-3697.patch

From 4de9de9d14f4ac27229e45514627534e32cc4406 Mon Sep 17 00:00:00 2001
From: Hitendra Prajapati <hprajapati@mvista.com>
Date: Tue, 19 Jul 2022 11:13:02 +0530
Subject: [PATCH] CVE-2021-3697

Upstream-Status: Backport [https://git.savannah.gnu.org/gitweb/?p=grub.git;a=commit;h=22a3f97d39f6a10b08ad7fd1cc47c4dcd10413f6]
CVE: CVE-2021-3697
Signed-off-by: Hitendra Prajapati <hprajapati@mvista.com>

video/readers/jpeg: Block int underflow -> wild pointer write

Certain 1 px wide images caused a wild pointer write in
grub_jpeg_ycrcb_to_rgb(). This was caused because in grub_jpeg_decode_data(),
we have the following loop:

for (; data->r1 < nr1 && (!data->dri || rst);
     data->r1++, data->bitmap_ptr += (vb * data->image_width - hb * nc1) * 3)

We did not check if vb * width >= hb * nc1.

On a 64-bit platform, if that turns out to be negative, it will underflow,
be interpreted as unsigned 64-bit, then be added to the 64-bit pointer, so
we see data->bitmap_ptr jump, e.g.:

0x6180_0000_0480 to
0x6181_0000_0498
     ^
     ~--- carry has occurred and this pointer is now far away from
          any object.

On a 32-bit platform, it will decrement the pointer, creating a pointer
that won't crash but will overwrite random data.

Catch the underflow and error out.

Fixes: CVE-2021-3697

Signed-off-by: Daniel Axtens <dja@axtens.net>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
---
 grub-core/video/readers/jpeg.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/grub-core/video/readers/jpeg.c b/grub-core/video/readers/jpeg.c
index 31359a4..545a60b 100644
--- a/grub-core/video/readers/jpeg.c
+++ b/grub-core/video/readers/jpeg.c
@@ -23,6 +23,7 @@
 #include <grub/mm.h>
 #include <grub/misc.h>
 #include <grub/bufio.h>
+#include <grub/safemath.h>
 
 GRUB_MOD_LICENSE ("GPLv3+");
 
@@ -617,6 +618,7 @@ static grub_err_t
 grub_jpeg_decode_data (struct grub_jpeg_data *data)
 {
   unsigned c1, vb, hb, nr1, nc1;
+  unsigned stride_a, stride_b, stride;
   int rst = data->dri;
 
   vb = 8 << data->log_vs;
@@ -624,8 +626,14 @@ grub_jpeg_decode_data (struct grub_jpeg_data *data)
   nr1 = (data->image_height + vb - 1) >> (3 + data->log_vs);
   nc1 = (data->image_width + hb - 1)  >> (3 + data->log_hs);
 
+  if (grub_mul(vb, data->image_width, &stride_a) ||
+      grub_mul(hb, nc1, &stride_b) ||
+      grub_sub(stride_a, stride_b, &stride))
+    return grub_error (GRUB_ERR_BAD_FILE_TYPE,
+		       "jpeg: cannot decode image with these dimensions");
+
   for (; data->r1 < nr1 && (!data->dri || rst);
-       data->r1++, data->bitmap_ptr += (vb * data->image_width - hb * nc1) * 3)
+       data->r1++, data->bitmap_ptr += stride * 3)
     for (c1 = 0;  c1 < nc1 && (!data->dri || rst);
 	c1++, rst--, data->bitmap_ptr += hb * 3)
       {
-- 
2.25.1