linux-cve-announce - CVE-2024-46695: selinux,smack: don't bypass permissions check in inode

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Message-ID: <2024091340-CVE-2024-46695-affc@gregkh>
Date: Fri, 13 Sep 2024 07:30:56 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2024-46695: selinux,smack: don't bypass permissions check in inode_setsecctx hook

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

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

selinux,smack: don't bypass permissions check in inode_setsecctx hook

Marek Gresko reports that the root user on an NFS client is able to
change the security labels on files on an NFS filesystem that is
exported with root squashing enabled.

The end of the kerneldoc comment for __vfs_setxattr_noperm() states:

 *  This function requires the caller to lock the inode's i_mutex before it
 *  is executed. It also assumes that the caller will make the appropriate
 *  permission checks.

nfsd_setattr() does do permissions checking via fh_verify() and
nfsd_permission(), but those don't do all the same permissions checks
that are done by security_inode_setxattr() and its related LSM hooks do.

Since nfsd_setattr() is the only consumer of security_inode_setsecctx(),
simplest solution appears to be to replace the call to
__vfs_setxattr_noperm() with a call to __vfs_setxattr_locked().  This
fixes the above issue and has the added benefit of causing nfsd to
recall conflicting delegations on a file when a client tries to change
its security label.

The Linux kernel CVE team has assigned CVE-2024-46695 to this issue.

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

	Fixed in 6.6.49 with commit 459584258d47
	Fixed in 6.10.8 with commit f71ec019257b
	Fixed in 6.11-rc6 with commit 76a0e79bc84f

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-2024-46695
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/selinux/hooks.c
	security/smack/smack_lsm.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/459584258d47ec3cc6245a82e8a49c9d08eb8b57
	https://git.kernel.org/stable/c/f71ec019257ba4f7ab198bd948c5902a207bad96
	https://git.kernel.org/stable/c/76a0e79bc84f466999fa501fce5bf7a07641b8a7