1bad507220
Details: https://lists.gnu.org/archive/html/grub-devel/2021-03/msg00007.html
As detailed in commit 7e64a050fb, it is
difficult to utilize the upstream patches directly, so a number of
patches include changes to generated files so that we don't need invoke
the gentpl.py script.
In addition to the security fixes, these required patches has been
backported:
f76a27996 efi: Make shim_lock GUID and protocol type public
04ae030d0 efi: Return grub_efi_status_t from grub_efi_get_variable()
ac5c93675 efi: Add a function to read EFI variables with attributes
d7e54b2e5 efi: Add secure boot detection
The following security issues are fixed:
CVE-2020-14372 grub2: The acpi command allows privileged user to load crafted
ACPI tables when Secure Boot is enabled
CWE-184
7.5/CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:H
GRUB2 enables the use of the command acpi even when Secure Boot is signaled by
the firmware. An attacker with local root privileges to can drop a small SSDT
in /boot/efi and modify grub.cfg to instruct grub to load said SSDT. The SSDT
then gets run by the kernel and it overwrites the kernel lock down configuration
enabling the attacker to load unsigned kernel modules and kexec unsigned code.
Reported-by: Máté Kukri
*******************************************************************************
CVE-2020-25632 grub2: Use-after-free in rmmod command
CWE-416
7.5/CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:H
The rmmod implementation for GRUB2 is flawed, allowing an attacker to unload
a module used as dependency without checking if any other dependent module is
still loaded. This leads to an use-after-free scenario possibly allowing an
attacker to execute arbitrary code and by-pass Secure Boot protections.
Reported-by: Chris Coulson (Canonical)
*******************************************************************************
CVE-2020-25647 grub2: Out-of-bound write in grub_usb_device_initialize()
CWE-787
6.9/CVSS:3.1/AV:P/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:H
grub_usb_device_initialize() is called to handle USB device initialization. It
reads out the descriptors it needs from the USB device and uses that data to
fill in some USB data structures. grub_usb_device_initialize() performs very
little bounds checking and simply assumes the USB device provides sane values.
This behavior can trigger memory corruption. If properly exploited, this would
lead to arbitrary code execution allowing the attacker to by-pass Secure Boot
mechanism.
Reported-by: Joseph Tartaro (IOActive) and Ilja van Sprundel (IOActive)
*******************************************************************************
CVE-2020-27749 grub2: Stack buffer overflow in grub_parser_split_cmdline
CWE-121
7.5/CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:H
grub_parser_split_cmdline() expands variable names present in the supplied
command line in to their corresponding variable contents and uses a 1kB stack
buffer for temporary storage without sufficient bounds checking. If the
function is called with a command line that references a variable with a
sufficiently large payload, it is possible to overflow the stack buffer,
corrupt the stack frame and control execution. An attacker may use this to
circumvent Secure Boot protections.
Reported-by: Chris Coulson (Canonical)
*******************************************************************************
CVE-2020-27779 grub2: The cutmem command allows privileged user to remove
memory regions when Secure Boot is enabled
CWE-285
7.5/CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:H
The GRUB2's cutmem command does not honor Secure Boot locking. This allows an
privileged attacker to remove address ranges from memory creating an
opportunity to circumvent Secure Boot protections after proper triage about
grub's memory layout.
Reported-by: Teddy Reed
*******************************************************************************
CVE-2021-3418 - grub2: GRUB 2.05 reintroduced CVE-2020-15705
CWE-281
6.4/CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
The GRUB2 upstream reintroduced the CVE-2020-15705. This refers to a distro
specific flaw which made upstream in the mentioned version.
If certificates that signed GRUB2 are installed into db, GRUB2 can be booted
directly. It will then boot any kernel without signature validation. The booted
kernel will think it was booted in Secure Boot mode and will implement lock
down, yet it could have been tampered.
This flaw only affects upstream and distributions using the shim_lock verifier.
Reported-by: Dimitri John Ledkov (Canonical)
*******************************************************************************
CVE-2021-20225 grub2: Heap out-of-bounds write in short form option parser
CWE-787
7.5/CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:H
The option parser in GRUB2 allows an attacker to write past the end of
a heap-allocated buffer by calling certain commands with a large number
of specific short forms of options.
Reported-by: Daniel Axtens (IBM)
*******************************************************************************
CVE-2021-20233 grub2: Heap out-of-bound write due to mis-calculation of
space required for quoting
CWE-787
7.5/CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:H
There's a flaw on GRUB2 menu rendering code setparam_prefix() in the menu
rendering code performs a length calculation on the assumption that expressing
a quoted single quote will require 3 characters, while it actually requires
4 characters. This allow an attacker to corrupt memory by one byte for each
quote in the input.
Reported-by: Daniel Axtens (IBM)
*******************************************************************************
Signed-off-by: Stefan Sørensen <stefan.sorensen@spectralink.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
88 lines
4.0 KiB
Diff
88 lines
4.0 KiB
Diff
From e346414725a70e5c74ee87ca14e580c66f517666 Mon Sep 17 00:00:00 2001
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From: Alex Burmashev <alexander.burmashev@oracle.com>
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Date: Tue, 16 Feb 2021 11:12:12 +0100
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Subject: [PATCH] templates: Disable the os-prober by default
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The os-prober is enabled by default what may lead to potentially
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dangerous use cases and borderline opening attack vectors. This
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patch disables the os-prober, adds warning messages and updates
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GRUB_DISABLE_OS_PROBER configuration option documentation. This
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way we make it clear that the os-prober usage is not recommended.
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Simplistic nature of this change allows downstream vendors, who
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really want os-prober to be enabled out of the box in their
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relevant products, easily revert to it's old behavior.
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Reported-by: NyankoSec (<nyanko@10x.moe>, https://twitter.com/NyankoSec),
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working with SSD Secure Disclosure
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Signed-off-by: Alex Burmashev <alexander.burmashev@oracle.com>
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Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
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Signed-off-by: Stefan Sørensen <stefan.sorensen@spectralink.com>
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---
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docs/grub.texi | 18 ++++++++++--------
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util/grub.d/30_os-prober.in | 5 ++++-
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2 files changed, 14 insertions(+), 9 deletions(-)
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diff --git a/docs/grub.texi b/docs/grub.texi
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index e302797..45a9f80 100644
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--- a/docs/grub.texi
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+++ b/docs/grub.texi
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@@ -1481,10 +1481,13 @@ boot sequence. If you have problems, set this option to @samp{text} and
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GRUB will tell Linux to boot in normal text mode.
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@item GRUB_DISABLE_OS_PROBER
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-Normally, @command{grub-mkconfig} will try to use the external
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-@command{os-prober} program, if installed, to discover other operating
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-systems installed on the same system and generate appropriate menu entries
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-for them. Set this option to @samp{true} to disable this.
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+The @command{grub-mkconfig} has a feature to use the external
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+@command{os-prober} program to discover other operating systems installed on
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+the same machine and generate appropriate menu entries for them. It is disabled
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+by default since automatic and silent execution of @command{os-prober}, and
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+creating boot entries based on that data, is a potential attack vector. Set
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+this option to @samp{false} to enable this feature in the
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+@command{grub-mkconfig} command.
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@item GRUB_OS_PROBER_SKIP_LIST
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List of space-separated FS UUIDs of filesystems to be ignored from os-prober
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@@ -1812,10 +1815,9 @@ than zero; otherwise 0.
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@section Multi-boot manual config
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Currently autogenerating config files for multi-boot environments depends on
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-os-prober and has several shortcomings. While fixing it is scheduled for the
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-next release, meanwhile you can make use of the power of GRUB syntax and do it
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-yourself. A possible configuration is detailed here, feel free to adjust to your
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-needs.
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+os-prober and has several shortcomings. Due to that it is disabled by default.
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+It is advised to use the power of GRUB syntax and do it yourself. A possible
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+configuration is detailed here, feel free to adjust to your needs.
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First create a separate GRUB partition, big enough to hold GRUB. Some of the
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following entries show how to load OS installer images from this same partition,
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diff --git a/util/grub.d/30_os-prober.in b/util/grub.d/30_os-prober.in
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index 515a68c..99de043 100644
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--- a/util/grub.d/30_os-prober.in
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+++ b/util/grub.d/30_os-prober.in
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@@ -26,7 +26,8 @@ export TEXTDOMAINDIR="@localedir@"
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. "$pkgdatadir/grub-mkconfig_lib"
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-if [ "x${GRUB_DISABLE_OS_PROBER}" = "xtrue" ]; then
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+if [ "x${GRUB_DISABLE_OS_PROBER}" = "xfalse" ]; then
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+ gettext_printf "os-prober will not be executed to detect other bootable partitions.\nSystems on them will not be added to the GRUB boot configuration.\nCheck GRUB_DISABLE_OS_PROBER documentation entry.\n"
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exit 0
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fi
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@@ -39,6 +40,8 @@ OSPROBED="`os-prober | tr ' ' '^' | paste -s -d ' '`"
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if [ -z "${OSPROBED}" ] ; then
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# empty os-prober output, nothing doing
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exit 0
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+else
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+ grub_warn "$(gettext_printf "os-prober was executed to detect other bootable partitions.\nIt's output will be used to detect bootable binaries on them and create new boot entries.")"
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fi
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osx_entry() {
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--
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2.14.2
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