From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754708Ab0JDKKm (ORCPT ); Mon, 4 Oct 2010 06:10:42 -0400 Received: from mail-fx0-f46.google.com ([209.85.161.46]:61909 "EHLO mail-fx0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754286Ab0JDKKk (ORCPT ); Mon, 4 Oct 2010 06:10:40 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=subject:from:to:cc:in-reply-to:references:content-type:date :message-id:mime-version:x-mailer:content-transfer-encoding; b=XnSAbj1wBs3TSMWCOO2XuQx4tK7BcQRqjrpvuykZNhHRLq6anhFHOxzBNbyRPyFwl2 OBbCJmcmhqN0BfN03hFS5IUklAD8liimt/30pssyW+NpJpj1EyqAbpGJ0Va9nP6j+2MR clqhRhSNMXrQUjYwxPlfyE97daGlBFGM9OVMQ= Subject: Re: [PATCH] sysctl: fix min/max handling in __do_proc_doulongvec_minmax() From: Eric Dumazet To: =?ISO-8859-1?Q?Am=E9rico?= Wang Cc: 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 In-Reply-To: <20101004093439.GG5189@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> Content-Type: text/plain; charset="UTF-8" Date: Mon, 04 Oct 2010 12:10:30 +0200 Message-ID: <1286187030.18293.33.camel@edumazet-laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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)