UBUNTU-CVE-2026-80928: High severity ubuntu/linux vulnerability

In the Linux kernel, the following vulnerability has been resolved: smack: fix cred UAF in smackfilesendsigiotask() When inspecting the credentials of another task, objective credentials (->realcred, accessed with taskcred()) must always be used. Accessing ->cred on a non-current task is forbidden unless that task is being created or destroyed; a task is allowed to change its own ->cred pointer with no synchronization, and changing ->cred should only affect the current syscall. smackfilesendsigiotask() was accessing both sets of credentials: First tsk->cred, then taskcred(tsk). Fix it, always access the objective credentials here. I have tested that this bug can lead to a KASAN-reported UAF of struct cred in smackfilesendsigiotask(), and that this fix prevents the race.