Message-ID: <2024120609-CVE-2024-53142-b75e@gregkh>
Date: Fri,  6 Dec 2024 10:37:08 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2024-53142: initramfs: avoid filename buffer overrun

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

initramfs: avoid filename buffer overrun

The initramfs filename field is defined in
Documentation/driver-api/early-userspace/buffer-format.rst as:

 37 cpio_file := ALGN(4) + cpio_header + filename + "\0" + ALGN(4) + data
...
 55 ============= ================== =========================
 56 Field name    Field size         Meaning
 57 ============= ================== =========================
...
 70 c_namesize    8 bytes            Length of filename, including final \0

When extracting an initramfs cpio archive, the kernel's do_name() path
handler assumes a zero-terminated path at @collected, passing it
directly to filp_open() / init_mkdir() / init_mknod().

If a specially crafted cpio entry carries a non-zero-terminated filename
and is followed by uninitialized memory, then a file may be created with
trailing characters that represent the uninitialized memory. The ability
to create an initramfs entry would imply already having full control of
the system, so the buffer overrun shouldn't be considered a security
vulnerability.

Append the output of the following bash script to an existing initramfs
and observe any created /initramfs_test_fname_overrunAA* path. E.g.
  ./reproducer.sh | gzip >> /myinitramfs

It's easiest to observe non-zero uninitialized memory when the output is
gzipped, as it'll overflow the heap allocated @out_buf in __gunzip(),
rather than the initrd_start+initrd_size block.

---- reproducer.sh ----
nilchar="A"	# change to "\0" to properly zero terminate / pad
magic="070701"
ino=1
mode=$(( 0100777 ))
uid=0
gid=0
nlink=1
mtime=1
filesize=0
devmajor=0
devminor=1
rdevmajor=0
rdevminor=0
csum=0
fname="initramfs_test_fname_overrun"
namelen=$(( ${#fname} + 1 ))	# plus one to account for terminator

printf "%s%08x%08x%08x%08x%08x%08x%08x%08x%08x%08x%08x%08x%08x%s" \
	$magic $ino $mode $uid $gid $nlink $mtime $filesize \
	$devmajor $devminor $rdevmajor $rdevminor $namelen $csum $fname

termpadlen=$(( 1 + ((4 - ((110 + $namelen) & 3)) % 4) ))
printf "%.s${nilchar}" $(seq 1 $termpadlen)
---- reproducer.sh ----

Symlink filename fields handled in do_symlink() won't overrun past the
data segment, due to the explicit zero-termination of the symlink
target.

Fix filename buffer overrun by aborting the initramfs FSM if any cpio
entry doesn't carry a zero-terminator at the expected (name_len - 1)
offset.

The Linux kernel CVE team has assigned CVE-2024-53142 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 2.6.12 with commit 1da177e4c3f4 and fixed in 4.19.325 with commit bb7ac96670ab
	Issue introduced in 2.6.12 with commit 1da177e4c3f4 and fixed in 6.11.11 with commit 49d01e736c30
	Issue introduced in 2.6.12 with commit 1da177e4c3f4 and fixed in 6.12.2 with commit fb83b093f758
	Issue introduced in 2.6.12 with commit 1da177e4c3f4 and fixed in 6.13-rc1 with commit e017671f534d

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2024-53142
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	init/initramfs.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/bb7ac96670ab1d8d681015f9d66e45dad579af4d
	https://git.kernel.org/stable/c/49d01e736c3045319e030d1e75fb983011abaca7
	https://git.kernel.org/stable/c/fb83b093f75806333b6f4ae29b158d2e0e3ec971
	https://git.kernel.org/stable/c/e017671f534dd3f568db9e47b0583e853d2da9b5

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