From mboxrd@z Thu Jan 1 00:00:00 1970 From: =?utf-8?Q?Am=C3=A9rico?= Wang Subject: Re: [PATCH] sysctl: fix min/max handling in __do_proc_doulongvec_minmax() Date: Mon, 4 Oct 2010 18:35:45 +0800 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-Transfer-Encoding: QUOTED-PRINTABLE 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 To: Eric Dumazet Return-path: Content-Disposition: inline In-Reply-To: <1286187030.18293.33.camel@edumazet-laptop> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Mon, Oct 04, 2010 at 12:10:30PM +0200, Eric Dumazet wrote: >Le lundi 04 octobre 2010 =C3=A0 17:34 +0800, Am=C3=A9rico Wang a =C3=A9= crit : >> On Mon, Oct 04, 2010 at 11:04:18AM +0200, Eric Dumazet wrote: >> >Le lundi 04 octobre 2010 =C3=A0 03:59 -0500, Robin Holt a =C3=A9cri= t : >> >> 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. >> >> >=20 >> >> > Noticed while doing some changes in network stack for the "16TB= problem" >> >> >=20 >> >> > Signed-off-by: Eric Dumazet >> >> > --- >> >> > kernel/sysctl.c | 3 ++- >> >> > 1 file changed, 2 insertions(+), 1 deletion(-) >> >> >=20 >> >> > 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(vo= id *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)) >> >>=20 >> >> How about changing: >> >> for (; left && vleft--; i++, min++, max++, first=3D0) { >> >> into: >> >> for (; left && vleft--; i++, min =3D min ? min + 1 : NULL= , max =3D max ? max + 1: NULL, first=3D0) { >> >>=20 >> >> That would make min and max correct and reduce the chances somebo= dy in >> >> the future overlooks the fact they are currently filled with garb= age. >> > >> >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... >> > >>=20 >> 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. >>=20 >> I see no problem with the original code, or I must have missed somet= hing? > >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 =3D NULL, .extra2 =3D NULL (no range checks, thi= s is a >valid use case) > >First element, min =3D NULL OK. no problem so far. > >Second element, min =3D (long *)(NULL + sizeof(long)) -> BUG=20 > >Third element, min =3D (long *)(NULL + 2*sizeof(long)) -> BUG=20 > >After my patch, min/max increases normally (they are only pointers aft= er >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.