Subject: CVE-2024-49883: ext4: aovid use-after-free in ext4_ext_insert_extent()

From: Greg Kroah-Hartman <[email-masked]>

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

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

ext4: aovid use-after-free in ext4_ext_insert_extent()

As Ojaswin mentioned in Link, in ext4_ext_insert_extent(), if the path is
reallocated in ext4_ext_create_new_leaf(), we'll use the stale path and
cause UAF. Below is a sample trace with dummy values:

ext4_ext_insert_extent
  path = *ppath = 2000
  ext4_ext_create_new_leaf(ppath)
    ext4_find_extent(ppath)
      path = *ppath = 2000
      if (depth > path[0].p_maxdepth)
            kfree(path = 2000);
            *ppath = path = NULL;
      path = kcalloc() = 3000
      *ppath = 3000;
      return path;
  /* here path is still 2000, UAF! */
  eh = path[depth].p_hdr

==================================================================
BUG: KASAN: slab-use-after-free in ext4_ext_insert_extent+0x26d4/0x3330
Read of size 8 at addr ffff8881027bf7d0 by task kworker/u36:1/179
CPU: 3 UID: 0 PID: 179 Comm: kworker/u6:1 Not tainted 6.11.0-rc2-dirty #866
Call Trace:
 <TASK>
 ext4_ext_insert_extent+0x26d4/0x3330
 ext4_ext_map_blocks+0xe22/0x2d40
 ext4_map_blocks+0x71e/0x1700
 ext4_do_writepages+0x1290/0x2800
[...]

Allocated by task 179:
 ext4_find_extent+0x81c/0x1f70
 ext4_ext_map_blocks+0x146/0x2d40
 ext4_map_blocks+0x71e/0x1700
 ext4_do_writepages+0x1290/0x2800
 ext4_writepages+0x26d/0x4e0
 do_writepages+0x175/0x700
[...]

Freed by task 179:
 kfree+0xcb/0x240
 ext4_find_extent+0x7c0/0x1f70
 ext4_ext_insert_extent+0xa26/0x3330
 ext4_ext_map_blocks+0xe22/0x2d40
 ext4_map_blocks+0x71e/0x1700
 ext4_do_writepages+0x1290/0x2800
 ext4_writepages+0x26d/0x4e0
 do_writepages+0x175/0x700
[...]
==================================================================

So use *ppath to update the path to avoid the above problem.

The Linux kernel CVE team has assigned CVE-2024-49883 to this issue.

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

	Issue introduced in 3.18 with commit 10809df84a4d and fixed in 5.10.227 with commit 5e811066c5ab
	Issue introduced in 3.18 with commit 10809df84a4d and fixed in 5.15.168 with commit 9df59009dfc6
	Issue introduced in 3.18 with commit 10809df84a4d and fixed in 6.1.113 with commit 51db04892a99
	Issue introduced in 3.18 with commit 10809df84a4d and fixed in 6.6.55 with commit 8162ee5d94b8
	Issue introduced in 3.18 with commit 10809df84a4d and fixed in 6.10.14 with commit beb7b66fb489
	Issue introduced in 3.18 with commit 10809df84a4d and fixed in 6.11.3 with commit bfed082ce4b1
	Issue introduced in 3.18 with commit 10809df84a4d and fixed in 6.12-rc1 with commit a164f3a432aa

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-2024-49883
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:
	fs/ext4/extents.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/5e811066c5ab709b070659197dccfb80ab650ddd
	https://git.kernel.org/stable/c/9df59009dfc6d9fc1bd9ddf6c5ab6e56d6ed887a
	https://git.kernel.org/stable/c/51db04892a993cace63415be99848970a0f15ef2
	https://git.kernel.org/stable/c/8162ee5d94b8c0351be0a9321be134872a7654a1
	https://git.kernel.org/stable/c/beb7b66fb489041c50c6473100b383f7a51648fc
	https://git.kernel.org/stable/c/bfed082ce4b1ce6349b05c09a0fa4f3da35ecb1b
	https://git.kernel.org/stable/c/a164f3a432aae62ca23d03e6d926b122ee5b860d