From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754910Ab0JDKbN (ORCPT ); Mon, 4 Oct 2010 06:31:13 -0400 Received: from mail-px0-f174.google.com ([209.85.212.174]:45481 "EHLO mail-px0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754797Ab0JDKbL (ORCPT ); Mon, 4 Oct 2010 06:31:11 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:content-transfer-encoding :in-reply-to:user-agent; b=xi4NJbPNxjxtYe7QDtxhhnncgfoE58LVtB6qarXPYWn/nm+3qt0QZ+2jPBZO/UgqTE f80IfFudRo0F/3uVaxuqfbekGJR221W9nZh6vsrN2BsVQ42oWNadt3LBHajiLyFvJhzI Jb7jyCmpxf2xLFXYutkBc14AXndRvT/ELc9ic= Date: Mon, 4 Oct 2010 18:35:45 +0800 From: =?utf-8?Q?Am=C3=A9rico?= Wang To: Eric Dumazet Cc: =?utf-8?Q?Am=C3=A9rico?= Wang , Robin Holt , Andrew Morton , linux-kernel , Willy Tarreau , "David S. Miller" , netdev@vger.kernel.org, James Morris , Hideaki YOSHIFUJI , "Pekka Savola (ipv6)" , Patrick McHardy , Alexey Kuznetsov Subject: Re: [PATCH] sysctl: fix min/max handling in __do_proc_doulongvec_minmax() Message-ID: <20101004103545.GJ5189@cr0.nay.redhat.com> References: <1286025469.2582.1806.camel@edumazet-laptop> <20101004085913.GR14068@sgi.com> <1286183058.18293.26.camel@edumazet-laptop> <20101004093439.GG5189@cr0.nay.redhat.com> <1286187030.18293.33.camel@edumazet-laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1286187030.18293.33.camel@edumazet-laptop> 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, Oct 04, 2010 at 12:10:30PM +0200, Eric Dumazet wrote: >Le lundi 04 octobre 2010 à 17:34 +0800, Américo Wang a écrit : >> On Mon, Oct 04, 2010 at 11:04:18AM +0200, Eric Dumazet wrote: >> >Le lundi 04 octobre 2010 à 03:59 -0500, Robin Holt a écrit : >> >> On Sat, Oct 02, 2010 at 03:17:49PM +0200, Eric Dumazet wrote: >> >> > When proc_doulongvec_minmax() is used with an array of longs, >> >> > and no min/max check requested (.extra1 or .extra2 being NULL), we >> >> > dereference a NULL pointer for the second element of the array. >> >> > >> >> > Noticed while doing some changes in network stack for the "16TB problem" >> >> > >> >> > Signed-off-by: Eric Dumazet >> >> > --- >> >> > kernel/sysctl.c | 3 ++- >> >> > 1 file changed, 2 insertions(+), 1 deletion(-) >> >> > >> >> > diff --git a/kernel/sysctl.c b/kernel/sysctl.c >> >> > index f88552c..4fba86d 100644 >> >> > --- a/kernel/sysctl.c >> >> > +++ b/kernel/sysctl.c >> >> > @@ -2500,7 +2500,8 @@ static int __do_proc_doulongvec_minmax(void *data, struct ctl_table *table, int >> >> > break; >> >> > if (neg) >> >> > continue; >> >> > - if ((min && val < *min) || (max && val > *max)) >> >> > + if ((table->extra1 && val < *min) || >> >> > + (table->extra2 && val > *max)) >> >> >> >> How about changing: >> >> for (; left && vleft--; i++, min++, max++, first=0) { >> >> into: >> >> for (; left && vleft--; i++, min = min ? min + 1 : NULL, max = max ? max + 1: NULL, first=0) { >> >> >> >> That would make min and max correct and reduce the chances somebody in >> >> the future overlooks the fact they are currently filled with garbage. >> > >> >I prefer my solution, because the check is done only in the 'write' >> >case, while its done also for 'read' in your solution, not counting the >> >for (;;) is really ugly... >> > >> >> Sorry, I still don't get the point here, min and max >> are pointers, they are already checked before dereferenced. >> After your patch, min and max will be still increased, while >> you are still checking ->extra{1,2} which is wrong. >> >> I see no problem with the original code, or I must have missed something? > >Please re-read again. I had crashes, so original code is bugyy. > >Say you call __do_proc_doulongvec_minmax() with an array of three >elements. And .extra1 = NULL, .extra2 = NULL (no range checks, this is a >valid use case) > >First element, min = NULL OK. no problem so far. > >Second element, min = (long *)(NULL + sizeof(long)) -> BUG > >Third element, min = (long *)(NULL + 2*sizeof(long)) -> BUG > >After my patch, min/max increases normally (they are only pointers after >all) > >But they are _dereferenced_ only if they were _not_ NULL at the >beginning (extra1 not NULL for *min, extra2 not NULL for *max) > Hmm, I see, thanks for explanation. Your patch does fix the problem, but seems not a good solution, we should skip all min/max checking if ->extra(1|2) is NULL, instead of checking it every time within the loop. Thanks.