[PATCH] capabilities: Use RCU to protect task lookup in sys_capget

[PATCH] capabilities: Use RCU to protect task lookup in sys_capget

[Thomas Gleixner]

cap_get_target_pid() protects the task lookup with tasklist_lock.
security_capget() is called under tasklist_lock as well but
tasklist_lock does not protect anything there. The capabilities are
protected by RCU already.

So tasklist_lock only protects the lookup and prevents the task going
away, which can be done with rcu_read_lock() as well.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 kernel/capability.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Index: linux-2.6-tip/kernel/capability.c
===================================================================
--- linux-2.6-tip.orig/kernel/capability.c
+++ linux-2.6-tip/kernel/capability.c
@@ -135,7 +135,7 @@ static inline int cap_get_target_pid(pid
 	if (pid && (pid != task_pid_vnr(current))) {
 		struct task_struct *target;
 
-		read_lock(&tasklist_lock);
+		rcu_read_lock();
 
 		target = find_task_by_vpid(pid);
 		if (!target)
@@ -143,7 +143,7 @@ static inline int cap_get_target_pid(pid
 		else
 			ret = security_capget(target, pEp, pIp, pPp);
 
-		read_unlock(&tasklist_lock);
+		rcu_read_unlock();
 	} else
 		ret = security_capget(current, pEp, pIp, pPp);
 

Re: [PATCH] capabilities: Use RCU to protect task lookup in sys_capget

[James Morris]

On Wed, 9 Dec 2009, Thomas Gleixner wrote:

> cap_get_target_pid() protects the task lookup with tasklist_lock.
> security_capget() is called under tasklist_lock as well but
> tasklist_lock does not protect anything there. The capabilities are
> protected by RCU already.
> 
> So tasklist_lock only protects the lookup and prevents the task going
> away, which can be done with rcu_read_lock() as well.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>


Applied to
git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/security-testing-2.6#next


-- 
James Morris
<jmorris@namei.org>