UBUNTU-CVE-2026-99226: Use After Free
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
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Compensating control
Update find_keyring_by_name() to use keyring->uid for the namespace mapping check instead of dereferencing keyring->user->uid.
Event History
Frequently Asked Questions
What conditions are required to trigger this issue?
The race requires a named session-keyring join to run concurrently with a privileged KEYCTL_CHOWN operation against a keyring. The ownership change must replace the keyring's last reference to its old dynamic key_user, allowing that account structure to be freed while lookup still reads its UID.
Who is realistically exposed?
Systems using the affected Ubuntu Linux kernel variants are exposed where users can perform named keyring joins and a privileged actor can issue KEYCTL_CHOWN concurrently. The provided information does not identify a specific default configuration or affected package version range.
What is the security impact of a successful race?
A successful race causes named keyring lookup to read freed memory, resulting in a use-after-free condition in the kernel key management subsystem. The provided data does not state whether this can be used for privilege escalation, information disclosure, or denial of service.
How does the resolved code avoid the race?
The fix uses the keyring's inline owner UID, keyring->uid, for the namespace mapping check rather than dereferencing keyring->user->uid. This avoids accessing the separately allocated key_user structure after it may have been released.