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authorThomas Gleixner <tglx@linutronix.de>2009-12-10 00:52:51 +0000
committerThomas Gleixner <tglx@linutronix.de>2009-12-10 23:04:11 +0100
commitd4581a239a40319205762b76c01eb6363f277efa (patch)
treed05b5f7103c9585e8485b581dc90f5a4ed9d18e3 /kernel/sys.c
parent7cf7db8df0b78076eafa4ead47559344ca7b7a43 (diff)
downloadlinux-d4581a239a40319205762b76c01eb6363f277efa.tar.bz2
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 <tglx@linutronix.de> LKML-Reference: <20091210004703.029784964@linutronix.de> Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'kernel/sys.c')
-rw-r--r--kernel/sys.c2
1 files changed, 2 insertions, 0 deletions
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;
}