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

Official 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.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/91da70a2e5c6f54e1316d51e0e6911e78ef5e09a
• https://git.kernel.org/stable/c/856cb3f05b49d23dc1542f78696e20c4ea6dd7de
• https://git.kernel.org/stable/c/f29c1ec0e7d8c887a91df3f93bb4617c0ac95c6a
• https://git.kernel.org/stable/c/17c93bcd17755523c21abb22cbf2a41a6eb0caaf
• 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