Subject: CVE-2024-49881: ext4: update orig_path in ext4_find_extent()

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

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

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

ext4: update orig_path in ext4_find_extent()

In ext4_find_extent(), if the path is not big enough, we free it and set
*orig_path to NULL. But after reallocating and successfully initializing
the path, we don't update *orig_path, in which case the caller gets a
valid path but a NULL ppath, and this may cause a NULL pointer dereference
or a path memory leak. For example:

ext4_split_extent
  path = *ppath = 2000
  ext4_find_extent
    if (depth > path[0].p_maxdepth)
      kfree(path = 2000);
      *orig_path = path = NULL;
      path = kcalloc() = 3000
  ext4_split_extent_at(*ppath = NULL)
    path = *ppath;
    ex = path[depth].p_ext;
    // NULL pointer dereference!

==================================================================
BUG: kernel NULL pointer dereference, address: 0000000000000010
CPU: 6 UID: 0 PID: 576 Comm: fsstress Not tainted 6.11.0-rc2-dirty #847
RIP: 0010:ext4_split_extent_at+0x6d/0x560
Call Trace:
 <TASK>
 ext4_split_extent.isra.0+0xcb/0x1b0
 ext4_ext_convert_to_initialized+0x168/0x6c0
 ext4_ext_handle_unwritten_extents+0x325/0x4d0
 ext4_ext_map_blocks+0x520/0xdb0
 ext4_map_blocks+0x2b0/0x690
 ext4_iomap_begin+0x20e/0x2c0
[...]
==================================================================

Therefore, *orig_path is updated when the extent lookup succeeds, so that
the caller can safely use path or *ppath.

The Linux kernel CVE team has assigned CVE-2024-49881 to this issue.

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

	Issue introduced in 3.18 with commit 10809df84a4d and fixed in 5.10.227 with commit 6766937d0327
	Issue introduced in 3.18 with commit 10809df84a4d and fixed in 5.15.168 with commit a9fcb1717d75
	Issue introduced in 3.18 with commit 10809df84a4d and fixed in 6.1.113 with commit 6801ed129820
	Issue introduced in 3.18 with commit 10809df84a4d and fixed in 6.6.55 with commit f55ecc58d07a
	Issue introduced in 3.18 with commit 10809df84a4d and fixed in 6.10.14 with commit b63481b3a388
	Issue introduced in 3.18 with commit 10809df84a4d and fixed in 6.11.3 with commit 11b230100d68
	Issue introduced in 3.18 with commit 10809df84a4d and fixed in 6.12-rc1 with commit 5b4b2dcace35

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-2024-49881
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
	fs/ext4/move_extent.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/6766937d0327000ac1b87c97bbecdd28b0dd6599
	https://git.kernel.org/stable/c/a9fcb1717d75061d3653ed69365c8d45331815cd
	https://git.kernel.org/stable/c/6801ed1298204d16a38571091e31178bfdc3c679
	https://git.kernel.org/stable/c/f55ecc58d07a6c1f6d6d5b5af125c25f8da0bda2
	https://git.kernel.org/stable/c/b63481b3a388ee2df9e295f97273226140422a42
	https://git.kernel.org/stable/c/11b230100d6801c014fab2afabc8bdea304c1b96
	https://git.kernel.org/stable/c/5b4b2dcace35f618fe361a87bae6f0d13af31bc1