From d4581a239a40319205762b76c01eb6363f277efa Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Thu, 10 Dec 2009 00:52:51 +0000 Subject: [PATCH] sys: Fix missing rcu protection for __task_cred() access commit c69e8d9 (CRED: Use RCU to access another task's creds and to release a task's own creds) added non rcu_read_lock() protected access to task creds of the target task in set_prio_one(). The comment above the function says: * - the caller must hold the RCU read lock The calling code in sys_setpriority does read_lock(&tasklist_lock) but not rcu_read_lock(). This works only when CONFIG_TREE_PREEMPT_RCU=n. With CONFIG_TREE_PREEMPT_RCU=y the rcu_callbacks can run in the tick interrupt when they see no read side critical section. There is another instance of __task_cred() in sys_setpriority() itself which is equally unprotected. Wrap the whole code section into a rcu read side critical section to fix this quick and dirty. Will be revisited in course of the read_lock(&tasklist_lock) -> rcu crusade. Oleg noted further: 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. Signed-off-by: Thomas Gleixner LKML-Reference: <20091210004703.029784964@linutronix.de> Acked-by: Paul E. McKenney --- kernel/sys.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/kernel/sys.c b/kernel/sys.c index 9968c5fb55b9..bc1dc61c31ed 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -163,6 +163,7 @@ SYSCALL_DEFINE3(setpriority, int, which, int, who, int, niceval) if (niceval > 19) niceval = 19; + rcu_read_lock(); read_lock(&tasklist_lock); switch (which) { case PRIO_PROCESS: @@ -200,6 +201,7 @@ SYSCALL_DEFINE3(setpriority, int, which, int, who, int, niceval) } out_unlock: read_unlock(&tasklist_lock); + rcu_read_unlock(); out: return error; } -- 2.20.1