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>

1 files changed, 2 insertions, 2 deletions

diff --git a/kernel/capability.c b/kernel/capability.c
index 7f876e60521f..9e4697e9b276 100644
--- 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);