Re: [patch 1/9] sys: Fix missing rcu protection for __task_cred() access

David Howells
2009-12-11T13:42:36Z

Thomas Gleixner <tglx@linutronix.de> wrote:

> commit c69e8d9 (CRED: Use RCU to access another task's creds and to
> release a task's own creds) added non rcu_read_lock() protected access
> to task creds of the target task in set_prio_one().
>
> The comment above the function says:
> * - the caller must hold the RCU read lock
>
> The calling code in sys_setpriority does read_lock(&tasklist_lock) but
> not rcu_read_lock(). This works only when CONFIG_TREE_PREEMPT_RCU=n.
> With CONFIG_TREE_PREEMPT_RCU=y the rcu_callbacks can run in the tick
> interrupt when they see no read side critical section.
>
> There is another instance of __task_cred() in sys_setpriority() itself
> which is equally unprotected.
>
> Wrap the whole code section into a rcu read side critical section to
> fix this quick and dirty.
>
> Will be revisited in course of the read_lock(&tasklist_lock) -> rcu
> crusade.
>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Cc: James Morris <jmorris@namei.org>
> Cc: linux-security-module@vger.kernel.org

Acked-by: David Howells <dhowells@redhat.com>