Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758297AbaD2RWN (ORCPT ); Tue, 29 Apr 2014 13:22:13 -0400 Received: from www.linutronix.de ([62.245.132.108]:42939 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757795AbaD2RWL (ORCPT ); Tue, 29 Apr 2014 13:22:11 -0400 Date: Tue, 29 Apr 2014 19:22:25 +0200 (CEST) From: Thomas Gleixner To: Jiri Bohac cc: linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] timer: prevent overflow in apply_slack In-Reply-To: <20140429111356.GA23888@midget.suse.cz> Message-ID: References: <20140417194215.GA10494@midget.suse.cz> <20140418152310.GA13654@midget.suse.cz> <20140429111356.GA23888@midget.suse.cz> User-Agent: Alpine 2.02 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 29 Apr 2014, Jiri Bohac wrote: > Thomas, does this make sense now, with the new description? Yep, except > On Fri, Apr 18, 2014 at 05:23:11PM +0200, Jiri Bohac wrote: > > On architectures with sizeof(int) < sizeof (long), the > > computation of mask inside apply_slack() can be undefined if the > > computed bit is > 32. > > > > E.g. with: expires = 0xffffe6f5 and slack = 25, we get: > > > > expires_limit = 0x20000000e > > bit = 33 > > mask = (1 << 33) - 1 /* undefined */ > > > > On x86, mask becomes 1 and and the slack is not applied properly. > > On s390, mask is -1, expires is set to 0 and the timer fires immediately. > > > > Signed-off-by: Jiri Bohac > > Suggested-by: Deborah Townsend > > > > diff --git a/kernel/timer.c b/kernel/timer.c > > index 87bd529..4c36c91 100644 > > --- a/kernel/timer.c > > +++ b/kernel/timer.c > > @@ -838,7 +838,7 @@ unsigned long apply_slack(struct timer_list *timer, unsigned long expires) > > > > bit = find_last_bit(&mask, BITS_PER_LONG); > > > > - mask = (1 << bit) - 1; > > + mask = (1LL << bit) - 1; This should be 1UL, shouldn't it? > > expires_limit = expires_limit & ~(mask); > > > > Thanks, > > -- > Jiri Bohac > SUSE Labs, SUSE CZ > > -- 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/