[PATCH] sys: Fix missing rcu protection for sys_getpriority.

[Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>]

Oleg Nesterov wrote:
> This also fixes another bug here. find_task_by_vpid() is not safe
> without rcu_read_lock(). I do not mean it is not safe to use the
> result, just find_pid_ns() by itself is not safe.
> 
> Usually tasklist gives enough protection, but if copy_process() fails
> it calls free_pid() lockless and does call_rcu(delayed_put_pid().
> This means, without rcu lock find_pid_ns() can't scan the hash table
> safely.

This bug for sys_setpriority() was fixed, but not fixed for sys_getpriority().
Why not to add it as well?
--------------------
[PATCH] sys: Fix missing rcu protection for sys_setpriority.

find_task_by_vpid() is not safe without rcu_read_lock().
2.6.33-rc7 got RCU protection for sys_setpriority() but missed it for
sys_getpriority().

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
---
 kernel/sys.c |    2 ++
 1 file changed, 2 insertions(+)

--- linux-2.6.33-rc7.orig/kernel/sys.c
+++ linux-2.6.33-rc7/kernel/sys.c
@@ -222,6 +222,7 @@ SYSCALL_DEFINE2(getpriority, int, which,
 	if (which > PRIO_USER || which < PRIO_PROCESS)
 		return -EINVAL;
 
+	rcu_read_lock();
 	read_lock(&tasklist_lock);
 	switch (which) {
 		case PRIO_PROCESS:
@@ -267,6 +268,7 @@ SYSCALL_DEFINE2(getpriority, int, which,
 	}
 out_unlock:
 	read_unlock(&tasklist_lock);
+	rcu_read_unlock();
 
 	return retval;
 }