From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Hemminger Subject: Re: Undefined behaviour of connect(fd, NULL, 0); Date: Wed, 31 Mar 2010 14:14:45 -0700 Message-ID: <20100331141445.031fc3fb@s6510> References: <20100331223637.31f5f6ed@notabene.brown> <20100331114936.3549ca90@s6510> <20100401072412.032aa8e6@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org To: Neil Brown Return-path: Received: from mail.vyatta.com ([76.74.103.46]:51345 "EHLO mail.vyatta.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932241Ab0CaVPN (ORCPT ); Wed, 31 Mar 2010 17:15:13 -0400 In-Reply-To: <20100401072412.032aa8e6@notabene.brown> Sender: netdev-owner@vger.kernel.org List-ID: On Thu, 1 Apr 2010 07:24:12 +1100 Neil Brown wrote: > On Wed, 31 Mar 2010 11:49:36 -0700 > Stephen Hemminger wrote: > > > On Wed, 31 Mar 2010 22:36:37 +1100 > > Neil Brown wrote: > > > > > > > > Hi Netdev. > > > > > > We have a customer who was reporting strangely unpredictable behaviour of an > > > in-house application that used networking. > > > > > > It called connect on a non-blocking socket and subsequently called > > > connect(fd, NULL, 0) > > > > > > to check if the connection had succeeded. > > > This would sometime "work" and sometimes close the connection. > > > > > > Looking at the code (sys_connect, move_addr_to_kernel, inet_stream_connect), > > > it seems that in this case an uninitialised on-stack address is passed > > > to inet_stream_connect and it makes a decision based on ->sa_family (which is > > > uninitialised). > > > > > > It seems clear that connect(fd, NULL, 0) is the wrong thing to do in this > > > circumstance, but I think it would be good if it failed consistently rather > > > than unpredictably. > > > > > > Would it be appropriate for move_addr_to_kernel to zero out the remainder of > > > the address? > > > memset(kaddr+ulen, 0, MAX_SOCK_ADDR-ulen); > > > ?? > > > > > > Then connect(fd, NULL, 0) would always break the connection. > > > > I think the problem is inet_stream_connect referencing past addr_len. > > > > --- a/net/ipv4/af_inet.c 2010-03-31 11:47:01.952910248 -0700 > > +++ b/net/ipv4/af_inet.c 2010-03-31 11:48:09.852938406 -0700 > > @@ -575,7 +575,7 @@ int inet_stream_connect(struct socket *s > > > > lock_sock(sk); > > > > - if (uaddr->sa_family == AF_UNSPEC) { > > + if (addr_len < sizeof(sa_family_t) || uaddr->sa_family == AF_UNSPEC) { > > err = sk->sk_prot->disconnect(sk, flags); > > sock->state = err ? SS_DISCONNECTING : SS_UNCONNECTED; > > goto out; > > Thanks for the reply. > > The implication of this patch is that > connect(fd, NULL, 0) > is actually a valid way to check if an in-progress connection has completed. > > Is that the intention? The rationale is that move_addr_to_kernel, explcitly allow addr=NULL with addr_len=0 so if it is allowed there why not let it through. The implication of this is that addr_len is the same as AF_UNSPEC. > Does all other address manipulation code check the addr_len ?? (probably). Not sure. Someone ought to check BSD/Solaris to see if there is some standard here.