From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753858Ab0H3TvN (ORCPT ); Mon, 30 Aug 2010 15:51:13 -0400 Received: from mail-bw0-f46.google.com ([209.85.214.46]:41630 "EHLO mail-bw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751911Ab0H3TvM (ORCPT ); Mon, 30 Aug 2010 15:51:12 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=sender:message-id:date:from:user-agent:mime-version:to:cc:subject :references:in-reply-to:x-enigmail-version:content-type :content-transfer-encoding; b=jWZBU7est91TlpIBq8kVNezwqjwyWLtFd1CEdMV0aDnYw0sKGDoVZVNsR6CHY9rstA TR5BtPu6u1ng5hia8M5eEoBr7QNQOgw/2nK1dvIuxP9H1FVjovTd1xuoUp47B4M2bWqD E6RvARbERKEfQhgTt04xcmVd/T2I2kyTVaY6w= Message-ID: <4C7C0BAB.3000709@suse.cz> Date: Mon, 30 Aug 2010 21:51:07 +0200 From: Jiri Slaby User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; cs-CZ; rv:1.9.2.8) Gecko/20100802 SUSE/3.1.2 Thunderbird/3.1.2 MIME-Version: 1.0 To: paulmck@linux.vnet.ibm.com 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 References: <20100830172631.GA11868@linux.vnet.ibm.com> In-Reply-To: <20100830172631.GA11868@linux.vnet.ibm.com> X-Enigmail-Version: 1.1.2 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. regards, -- js suse labs