From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Biggers Subject: Re: [PATCH net] KEYS: DNS: fix parsing multiple options Date: Mon, 11 Jun 2018 10:57:42 -0700 Message-ID: <20180611175742.GA33284@gmail.com> References: <20180608162037.129802-1-ebiggers3@gmail.com> <20180611094022.gvrefejktxzw44i7@netronome.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: netdev@vger.kernel.org, "David S . Miller" , keyrings@vger.kernel.org, David Howells , Wang Lei , Eric Biggers To: Simon Horman Return-path: Received: from mail-pf0-f196.google.com ([209.85.192.196]:35248 "EHLO mail-pf0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932292AbeFKR5p (ORCPT ); Mon, 11 Jun 2018 13:57:45 -0400 Content-Disposition: inline In-Reply-To: <20180611094022.gvrefejktxzw44i7@netronome.com> Sender: netdev-owner@vger.kernel.org List-ID: Hi Simon, On Mon, Jun 11, 2018 at 11:40:23AM +0200, Simon Horman wrote: > On Fri, Jun 08, 2018 at 09:20:37AM -0700, Eric Biggers wrote: > > From: Eric Biggers > > > > My recent fix for dns_resolver_preparse() printing very long strings was > > incomplete, as shown by syzbot which still managed to hit the > > WARN_ONCE() in set_precision() by adding a crafted "dns_resolver" key: > > > > precision 50001 too large > > WARNING: CPU: 7 PID: 864 at lib/vsprintf.c:2164 vsnprintf+0x48a/0x5a0 > > > > The bug this time isn't just a printing bug, but also a logical error > > when multiple options ("#"-separated strings) are given in the key > > payload. Specifically, when separating an option string into name and > > value, if there is no value then the name is incorrectly considered to > > end at the end of the key payload, rather than the end of the current > > option. This bypasses validation of the option length, and also means > > that specifying multiple options is broken -- which presumably has gone > > unnoticed as there is currently only one valid option anyway. > > > > Fix it by correctly calculating the length of the option name. > > > > Reproducer: > > > > perl -e 'print "#A#", "\x00" x 50000' | keyctl padd dns_resolver desc @s > > > > Fixes: 4a2d789267e0 ("DNS: If the DNS server returns an error, allow that to be cached [ver #2]") > > Signed-off-by: Eric Biggers > > --- > > net/dns_resolver/dns_key.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/net/dns_resolver/dns_key.c b/net/dns_resolver/dns_key.c > > index 40c851693f77e..d448823d4d2ed 100644 > > --- a/net/dns_resolver/dns_key.c > > +++ b/net/dns_resolver/dns_key.c > > @@ -97,7 +97,7 @@ dns_resolver_preparse(struct key_preparsed_payload *prep) > > return -EINVAL; > > } > > > > - eq = memchr(opt, '=', opt_len) ?: end; > > + eq = memchr(opt, '=', opt_len) ?: next_opt; > > opt_nlen = eq - opt; > > eq++; > > It seems risky to advance eq++ in the case there the value is empty. > Its not not pointing to the value but it may be accessed twice further on > in this loop. > Sure, that's a separate existing issue though, and it must be checked that the value is present before using it anyway, which the code already does, so it's not a "real" bug. I think I'll keep this patch simple and leave that part as-is for now. Eric