capabilities: Use RCU to protect task lookup in sys_capget

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>
Signed-off-by: James Morris <jmorris@namei.org>

diff --git a/kernel/capability.c b/kernel/capability.c
index 7f876e6..9e4697e 100644 (file)
--- a/kernel/capability.c
+++ b/kernel/capability.c
@@ -135,7 +135,7 @@ static inline int cap_get_target_pid(pid_t pid, kernel_cap_t *pEp,
        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_t pid, kernel_cap_t *pEp,
                else
                        ret = security_capget(target, pEp, pIp, pPp);
 
-               read_unlock(&tasklist_lock);
+               rcu_read_unlock();
        } else
                ret = security_capget(current, pEp, pIp, pPp);