CVE-2026-68149: fs: preserve ACL_DONT_CACHE state in forget_cached_acl()

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

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

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

fs: preserve ACL_DONT_CACHE state in forget_cached_acl()

The ACL_DONT_CACHE state is meant to be a constant state for the inode
for filesystems that want to opt out of posix acl caching.

Commit facd61053cff1 ("fuse: fixes after adapting to new posix acl api")
used this facility to opt out of posix acl caching for fuse inodes with
fuse server that does not negotiate FUSE_POSIX_ACL (fc->posix_acl).

The commit also takes care to gate the forget_all_cached_acls() call in
fuse_set_acl() on fc->posix_acl because there is no need for it, but
there are other placed in fuse code which call forget_all_cached_acls()
unconditional to fc->posix_acl and those cause the loss of the
ACL_DONT_CACHE state.

This is not only a functional bug. Properly timed, a get_acl() from this
fuse filesystem can return a stale cached value, as was observed in tests,
because set_acl() does not invalidate the unintentional acl cache.

We could fix this in fuse, but it actually makes no sense for the vfs
helper forget_cached_acl() to invalidate the ACL_DONT_CACHE state, so
let it not do that to fix fuse and future users of ACL_DONT_CACHE.

The Linux kernel CVE team has assigned CVE-2026-68149 to this issue.


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

	Issue introduced in 6.2 with commit facd61053cff100973921d4d45d47cf53c747ec6 and fixed in 6.6.148 with commit b98fad81f1202b0eb26aacf3ff4cc7a21ed3b5bf
	Issue introduced in 6.2 with commit facd61053cff100973921d4d45d47cf53c747ec6 and fixed in 6.12.101 with commit 834ddf899484a2f23129080e8773bc04f4691d07
	Issue introduced in 6.2 with commit facd61053cff100973921d4d45d47cf53c747ec6 and fixed in 6.18.42 with commit a019b074903b3ad0a9726087efd0e8291452023b
	Issue introduced in 6.2 with commit facd61053cff100973921d4d45d47cf53c747ec6 and fixed in 7.1.6 with commit ca03a7984a34f48085fd013e0d2cf4e6420b4acf
	Issue introduced in 6.2 with commit facd61053cff100973921d4d45d47cf53c747ec6 and fixed in 7.2-rc5 with commit 4b9a5458d02e214ef2b384124ca626e3e381d778

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-2026-68149
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/posix_acl.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/b98fad81f1202b0eb26aacf3ff4cc7a21ed3b5bf
	https://git.kernel.org/stable/c/834ddf899484a2f23129080e8773bc04f4691d07
	https://git.kernel.org/stable/c/a019b074903b3ad0a9726087efd0e8291452023b
	https://git.kernel.org/stable/c/ca03a7984a34f48085fd013e0d2cf4e6420b4acf
	https://git.kernel.org/stable/c/4b9a5458d02e214ef2b384124ca626e3e381d778