commit a846a1954b6397e844fe1e258af7598897ec6159
author Pavel Emelyanov <xemul@openvz.org> Mon Mar 24 12:29:52 2008 -0700
committer Linus Torvalds <torvalds@linux-foundation.org> Mon Mar 24 19:22:19 2008 -0700
tree a90b3a593d528c299fd90e9e84fe17a7cdb23733
parent 4dd4b920218326231156c7991ce5b94afad841c3

bsd_acct: plain current->real_parent access is not always safe

This is minor, but dereferencing even current real_parent is not safe on debug
kernels, since the memory, this points to, can be unmapped - RCU protection is
required.

Besides, the tgid field is deprecated and is to be replaced with task_tgid_xxx
call (the 2nd patch), so RCU will be required anyway.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/acct.c

diff --git a/kernel/acct.c b/kernel/acct.c
index 521dfa5..7ff5339 100644
--- a/kernel/acct.c
+++ b/kernel/acct.c
@@ -482,7 +482,9 @@
 #endif
 #if ACCT_VERSION==3
 	ac.ac_pid = current->tgid;
-	ac.ac_ppid = current->real_parent->tgid;
+	rcu_read_lock();
+	ac.ac_ppid = rcu_dereference(current->real_parent)->tgid;
+	rcu_read_unlock();
 #endif
 
 	spin_lock_irq(&current->sighand->siglock);