From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755773Ab0H3Ucn (ORCPT ); Mon, 30 Aug 2010 16:32:43 -0400 Received: from e6.ny.us.ibm.com ([32.97.182.146]:46723 "EHLO e6.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755495Ab0H3Ucm (ORCPT ); Mon, 30 Aug 2010 16:32:42 -0400 Date: Mon, 30 Aug 2010 13:32:33 -0700 From: "Paul E. McKenney" To: Jiri Slaby Cc: linux-kernel@vger.kernel.org, mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca, josh@joshtriplett.org, dvhltc@us.ibm.com, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, jmorris@namei.org, Oleg Nesterov Subject: Re: [PATCH RFC] pid: make setpgid() system call use RCU read-side critical section Message-ID: <20100830203233.GK2420@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20100830172631.GA11868@linux.vnet.ibm.com> <4C7C0BAB.3000709@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4C7C0BAB.3000709@suse.cz> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Aug 30, 2010 at 09:51:07PM +0200, Jiri Slaby wrote: > Ccing Oleg. > > On 08/30/2010 07:26 PM, Paul E. McKenney wrote: > > [ 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. > > > > Located-by: Andrew Morton > > Signed-off-by: Paul E. McKenney > > --- > > > > sys.c | 2 ++ > > 1 file changed, 2 insertions(+) > > > > diff --git a/kernel/sys.c b/kernel/sys.c > > index e9ad444..05a4b0c 100644 > > --- a/kernel/sys.c > > +++ b/kernel/sys.c > > @@ -938,6 +938,7 @@ SYSCALL_DEFINE2(setpgid, pid_t, pid, pid_t, pgid) > > write_lock_irq(&tasklist_lock); > > > > err = -ESRCH; > > + rcu_read_lock(); > > p = find_task_by_vpid(pid); > > AFAICT the missing lock doesn't harm due to the write_lock of tasklist > above. But is probably a good thing to do anyway. Or we can add the tasklist lock to the rcu_dereference_check() condition. Thanx, Paul > regards, > -- > js > suse labs > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/