CVE-2026-97564: smb: client: reject userspace cifs.idmap descriptions

CVE-2026-97564: smb: client: reject userspace cifs.idmap descriptions

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

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

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

smb: client: reject userspace cifs.idmap descriptions

cifs.idmap key descriptions carry authority-bearing fields (owner and
group SIDs and uid/gid values in "os:"/"gs:"/"oi:"/"gi:" form) that the
cifs.idmap upcall helper treats as kernel-originating inputs.  Unlike
its sibling cifs.spnego, the cifs.idmap key type has no vet_description
hook, so userspace can create keys of this type through
request_key(2)/add_key(2) and supply those fields without CIFS origin.
A request_key(2) call with a non-NULL callout then drives a root
usermodehelper upcall (/sbin/request-key -> cifs.idmap) that consumes
the unvetted description in root context.

Only accept cifs.idmap descriptions while CIFS is using its private
root_cred to request the key.  id_to_sid()/sid_to_id() already run
under override_creds(root_cred), so the kernel-originated path is
unaffected.

This mirrors commit 3da1fdf4efbc ("smb: client: reject userspace
cifs.spnego descriptions"), which applied the same restriction to
cifs.spnego.

The Linux kernel CVE team has assigned CVE-2026-97564 to this issue.


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

	Issue introduced in 3.0 with commit 4d79dba0e00749fa40de8ef13a9b85ce57a1603b and fixed in 6.12.111 with commit e5964064e3fbe6325893408faff08ca33de0e2c3
	Issue introduced in 3.0 with commit 4d79dba0e00749fa40de8ef13a9b85ce57a1603b and fixed in 6.18.53 with commit 96751028c0d4dec785709ea3eb0ab38a4f2ded96
	Issue introduced in 3.0 with commit 4d79dba0e00749fa40de8ef13a9b85ce57a1603b and fixed in 7.2.7 with commit 1d3b24b16a0b013792e8f1e3ed060f0b46f537d1
	Issue introduced in 3.0 with commit 4d79dba0e00749fa40de8ef13a9b85ce57a1603b and fixed in 7.3-rc3 with commit d9d7eeb0cea5b55b82888f443622fd8d4ee064f3

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-2026-97564
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/smb/client/cifsacl.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/e5964064e3fbe6325893408faff08ca33de0e2c3
	https://git.kernel.org/stable/c/96751028c0d4dec785709ea3eb0ab38a4f2ded96
	https://git.kernel.org/stable/c/1d3b24b16a0b013792e8f1e3ed060f0b46f537d1
	https://git.kernel.org/stable/c/d9d7eeb0cea5b55b82888f443622fd8d4ee064f3