CVE-2026-99226: keys: Avoid the owner account dereference in named keyring lookup

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

keys: Avoid the owner account dereference in named keyring lookup

Named keyring lookup must keep the storage containing the owner UID alive through the namespace mapping check. findkeyringbyname() reads keyring->user->uid under keyringnamelock, but that lock protects the keyring's name entry and allocation, not its separate keyuser.

A named session-keyring join can overlap a privileged KEYCTLCHOWN on another CPU. If the keyring holds the last reference to its old dynamic keyuser and the ownership transfer succeeds, the following ordering is possible:

Named join Chown findkeyringbyname() keyctlchownkey() readlock(keyringnamelock) downwrite(key->sem) load old keyring->user replace key->user and key->uid upwrite(key->sem) keyput(key) keyuserput(old user): free read old user->uid readunlock(keyringnamelock)

Chown neither takes keyringnamelock nor keysessionmutex, so it can free the old account between the pointer load and the UID read. The lookup then reads freed memory even though the keyring itself is alive.

Use keyring->uid for the mapping check. keyalloc() initializes this inline owner UID and keyctlchownkey() updates it on chown. The existing name lock keeps its containing keyring allocated throughout the check, so lookup no longer depends on the account's lifetime. This also matches the owner UID used by the permission check.

KASAN report as below:

BUG: KASAN: slab-use-after-free in findkeyringbyname+0x577/0x5d0 Read of size 4 at addr ffff8881128ae2ec by task keycase/500