Subject: CVE-2024-40938: landlock: Fix d_parent walk

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

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

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

landlock: Fix d_parent walk

The WARN_ON_ONCE() in collect_domain_accesses() can be triggered when
trying to link a root mount point.  This cannot work in practice because
this directory is mounted, but the VFS check is done after the call to
security_path_link().

Do not use source directory's d_parent when the source directory is the
mount point.

[mic: Fix commit message]

The Linux kernel CVE team has assigned CVE-2024-40938 to this issue.

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

	Issue introduced in 5.19 with commit b91c3e4ea756 and fixed in 6.1.95 with commit b6e5e6964358
	Issue introduced in 5.19 with commit b91c3e4ea756 and fixed in 6.6.35 with commit cc30d05b34f9
	Issue introduced in 5.19 with commit b91c3e4ea756 and fixed in 6.9.6 with commit c7618c7b0b8c
	Issue introduced in 5.19 with commit b91c3e4ea756 and fixed in 6.10 with commit 88da52ccd66e

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-2024-40938
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:
	security/landlock/fs.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/b6e5e696435832b33e40775f060ef5c95f4fda1f
	https://git.kernel.org/stable/c/cc30d05b34f9a087a6928d09b131f7b491e9ab11
	https://git.kernel.org/stable/c/c7618c7b0b8c45bcef34410cc1d1e953eb17f8f6
	https://git.kernel.org/stable/c/88da52ccd66e65f2e63a6c35c9dff55d448ef4dc