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

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