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Fix a segfault in grub2-editenv when attempting to shrink a variable

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Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
This commit is contained in:
Javier Martinez Canillas 2020-05-12 20:16:59 +02:00
parent b914a7e168
commit 107dc9a693
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3 changed files with 65 additions and 1 deletions
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60
0213-envblk-Fix-buffer-overrun-when-attempting-to-shrink-.patch Normal file
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@ -0,0 +1,60 @@
From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Javier Martinez Canillas <javierm@redhat.com>
Date: Tue, 12 May 2020 01:00:51 +0200
Subject: [PATCH] envblk: Fix buffer overrun when attempting to shrink a
variable value
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
If an existing variable is set with a value whose length is smaller than
the current value, a memory corruption can happen due copying padding '#'
characters outside of the environment block buffer.
This is caused by a wrong calculation of the previous free space position
after moving backward the characters that followed the old variable value.
That position is calculated to fill the remaining of the buffer with the
padding '#' characters. But since isn't calculated correctly, it can lead
to copies outside of the buffer.
The issue can be reproduced by creating a variable with a large value and
then try to set a new value that is much smaller:
$ grub2-editenv --version
grub2-editenv (GRUB) 2.04
$ grub2-editenv env create
$ grub2-editenv env set a="$(for i in {1..500}; do var="b$var"; done; echo $var)"
$ wc -c env
1024 grubenv
$ grub2-editenv env set a="$(for i in {1..50}; do var="b$var"; done; echo $var)"
malloc(): corrupted top size
Aborted (core dumped)
$ wc -c env
0 grubenv
Reported-by: Renaud Métrich <rmetrich@redhat.com>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Patch-cc: Daniel Kiper <daniel.kiper@oracle.com>
---
grub-core/lib/envblk.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/grub-core/lib/envblk.c b/grub-core/lib/envblk.c
index f89d86d4e8d..874506da169 100644
--- a/grub-core/lib/envblk.c
+++ b/grub-core/lib/envblk.c
@@ -143,7 +143,7 @@ grub_envblk_set (grub_envblk_t envblk, const char *name, const char *value)
/* Move the following characters backward, and fill the new
space with harmless characters. */
grub_memmove (p + vl, p + len, pend - (p + len));
- grub_memset (space + len - vl, '#', len - vl);
+ grub_memset (space - (len - vl), '#', len - vl);
}
else
/* Move the following characters forward. */

1
grub.patches
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@ -210,3 +210,4 @@ Patch0209: 0209-10_linux.in-Enable-BLS-configuration-if-new-kernel-p.patch
Patch0210: 0210-efi-Set-image-base-address-before-jumping-to-the-PE-.patch
Patch0211: 0211-blscfg-Lookup-default_kernelopts-variable-as-fallbac.patch
Patch0212: 0212-10_linux.in-fix-early-exit-due-error-when-reading-pe.patch
Patch0213: 0213-envblk-Fix-buffer-overrun-when-attempting-to-shrink-.patch

5
grub2.spec
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@ -9,7 +9,7 @@
Name: grub2
Epoch: 1
Version: 2.04
Release: 15%{?dist}
Release: 16%{?dist}
Summary: Bootloader with support for Linux, Multiboot and more
License: GPLv3+
URL: http://www.gnu.org/software/grub/
@ -504,6 +504,9 @@ rm -r /boot/grub2.tmp/ || :
%endif
%changelog
* Tue May 12 2020 Javier Martinez Canillas <javierm@redhat.com> - 2.04-16
- Fix a segfault in grub2-editenv when attempting to shrink a variable
* Thu Apr 30 2020 Javier Martinez Canillas <javierm@redhat.com> - 2.04-15
- blscfg: Lookup default_kernelopts variable as fallback for options
Related: rhbz#1765297