From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933258Ab0IXQpI (ORCPT ); Fri, 24 Sep 2010 12:45:08 -0400 Received: from kroah.org ([198.145.64.141]:37146 "EHLO coco.kroah.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932985Ab0IXQfK (ORCPT ); Fri, 24 Sep 2010 12:35:10 -0400 X-Mailbox-Line: From gregkh@clark.site Fri Sep 24 09:33:46 2010 Message-Id: <20100924163346.188310596@clark.site> User-Agent: quilt/0.48-11.2 Date: Fri, 24 Sep 2010 09:31:48 -0700 From: Greg KH To: linux-kernel@vger.kernel.org, stable@kernel.org Cc: stable-review@kernel.org, torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, "Paul E. McKenney" , David Howells , Jiri Slaby , Oleg Nesterov Subject: [24/68] pid: make setpgid() system call use RCU read-side critical section In-Reply-To: <20100924163357.GA15741@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2.6.32-stable review patch. If anyone has any objections, please let us know. ------------------ From: Paul E. McKenney commit 950eaaca681c44aab87a46225c9e44f902c080aa upstream. [ 23.584719] [ 23.584720] =================================================== [ 23.585059] [ INFO: suspicious rcu_dereference_check() usage. ] [ 23.585176] --------------------------------------------------- [ 23.585176] kernel/pid.c:419 invoked rcu_dereference_check() without protection! [ 23.585176] [ 23.585176] other info that might help us debug this: [ 23.585176] [ 23.585176] [ 23.585176] rcu_scheduler_active = 1, debug_locks = 1 [ 23.585176] 1 lock held by rc.sysinit/728: [ 23.585176] #0: (tasklist_lock){.+.+..}, at: [] sys_setpgid+0x5f/0x193 [ 23.585176] [ 23.585176] stack backtrace: [ 23.585176] Pid: 728, comm: rc.sysinit Not tainted 2.6.36-rc2 #2 [ 23.585176] Call Trace: [ 23.585176] [] lockdep_rcu_dereference+0x99/0xa2 [ 23.585176] [] find_task_by_pid_ns+0x50/0x6a [ 23.585176] [] find_task_by_vpid+0x1d/0x1f [ 23.585176] [] sys_setpgid+0x67/0x193 [ 23.585176] [] system_call_fastpath+0x16/0x1b [ 24.959669] type=1400 audit(1282938522.956:4): avc: denied { module_request } for pid=766 comm="hwclock" kmod="char-major-10-135" scontext=system_u:system_r:hwclock_t:s0 tcontext=system_u:system_r:kernel_t:s0 tclas It turns out that the setpgid() system call fails to enter an RCU read-side critical section before doing a PID-to-task_struct translation. This commit therefore does rcu_read_lock() before the translation, and also does rcu_read_unlock() after the last use of the returned pointer. Reported-by: Andrew Morton Signed-off-by: Paul E. McKenney Acked-by: David Howells Cc: Jiri Slaby Cc: Oleg Nesterov Signed-off-by: Greg Kroah-Hartman --- kernel/sys.c | 2 ++ 1 file changed, 2 insertions(+) --- a/kernel/sys.c +++ b/kernel/sys.c @@ -962,6 +962,7 @@ SYSCALL_DEFINE2(setpgid, pid_t, pid, pid pgid = pid; if (pgid < 0) return -EINVAL; + rcu_read_lock(); /* From this point forward we keep holding onto the tasklist lock * so that our parent does not change from under us. -DaveM @@ -1015,6 +1016,7 @@ SYSCALL_DEFINE2(setpgid, pid_t, pid, pid out: /* All paths lead to here, thus we are safe. -DaveM */ write_unlock_irq(&tasklist_lock); + rcu_read_unlock(); return err; }