CVE-2026-74359: configfs_lookup(): don't leave ->s_dentry dangling on failure

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

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

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

configfs_lookup(): don't leave ->s_dentry dangling on failure

Normally ->s_dentry is cleared when dentry it's pointing to becomes
negative (on eviction, realistically).  However, that only happens
if dentry gets to be positive in the first place; in case of inode
allocation failure dentry never becomes positive, so ->d_iput()
is not called at all.

We do part of what normally would've been done by configfs_d_iput()
(dropping the reference to configfs_dirent) manually, but we do
not clear ->s_dentry there.  Sloppy as it is, it does not matter in
case of configfs_create_{dir,link}() - there configfs_dirent does
not survive dropping the sole reference to it.

However, for configfs_lookup() it *does* survive, with a dangling
pointer to soon to be freed dentry sitting it its ->s_dentry.

Subsequent getdents(2) in that directory will end up dereferencing
that pointer in order to pick the inode number.  Use after free...

This is the minimal fix; the right approach is to set the linkage
between dentry and configfs_dirent only after we know that we have
an inode, but that takes more surgery and the bug had been there
since 2006, so...

The Linux kernel CVE team has assigned CVE-2026-74359 to this issue.


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

	Issue introduced in 2.6.16 with commit 3d0f89bb169482d26d5aa4e82e763077e7e9bc4d and fixed in 5.15.212 with commit 3e83b2203aa59bd279e4f677ec793d49dc9d019e
	Issue introduced in 2.6.16 with commit 3d0f89bb169482d26d5aa4e82e763077e7e9bc4d and fixed in 6.1.178 with commit b6e9c82522ddaa3ac0706b295ff4a71975d4f883
	Issue introduced in 2.6.16 with commit 3d0f89bb169482d26d5aa4e82e763077e7e9bc4d and fixed in 6.6.145 with commit eee07d769da5ac4e4f7bd0bc17828646a318d499
	Issue introduced in 2.6.16 with commit 3d0f89bb169482d26d5aa4e82e763077e7e9bc4d and fixed in 6.12.97 with commit 9c747dcee164ead300de90550ad9e4122f0d1bbb
	Issue introduced in 2.6.16 with commit 3d0f89bb169482d26d5aa4e82e763077e7e9bc4d and fixed in 6.18.40 with commit c3b073a209a9baa691b744318ac929fecdd8847c
	Issue introduced in 2.6.16 with commit 3d0f89bb169482d26d5aa4e82e763077e7e9bc4d and fixed in 7.1.5 with commit 57088b06109f3222963c639d8d743f42c2899b13
	Issue introduced in 2.6.16 with commit 3d0f89bb169482d26d5aa4e82e763077e7e9bc4d and fixed in 7.2-rc1 with commit 10da12d352b7b2bb330a8609fdda9a58bf0e9856

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-2026-74359
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/configfs/dir.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/3e83b2203aa59bd279e4f677ec793d49dc9d019e
	https://git.kernel.org/stable/c/b6e9c82522ddaa3ac0706b295ff4a71975d4f883
	https://git.kernel.org/stable/c/eee07d769da5ac4e4f7bd0bc17828646a318d499
	https://git.kernel.org/stable/c/9c747dcee164ead300de90550ad9e4122f0d1bbb
	https://git.kernel.org/stable/c/c3b073a209a9baa691b744318ac929fecdd8847c
	https://git.kernel.org/stable/c/57088b06109f3222963c639d8d743f42c2899b13
	https://git.kernel.org/stable/c/10da12d352b7b2bb330a8609fdda9a58bf0e9856