Patchwork Undefined behaviour of connect(fd, NULL, 0);

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Submitter stephen hemminger
Date March 31, 2010, 6:49 p.m.
Message ID <20100331114936.3549ca90@s6510>
Download mbox | patch
Permalink /patch/49171/
State RFC
Delegated to: David Miller
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Comments

stephen hemminger - March 31, 2010, 6:49 p.m.
On Wed, 31 Mar 2010 22:36:37 +1100
Neil Brown <neilb@suse.de> 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.


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Neil Brown - March 31, 2010, 8:24 p.m.
On Wed, 31 Mar 2010 11:49:36 -0700
Stephen Hemminger <shemminger@vyatta.com> wrote:

> On Wed, 31 Mar 2010 22:36:37 +1100
> Neil Brown <neilb@suse.de> 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?

Does all other address manipulation code check the addr_len ?? (probably).

Thanks,
NeilBrown
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stephen hemminger - March 31, 2010, 9:14 p.m.
On Thu, 1 Apr 2010 07:24:12 +1100
Neil Brown <neilb@suse.de> wrote:

> On Wed, 31 Mar 2010 11:49:36 -0700
> Stephen Hemminger <shemminger@vyatta.com> wrote:
> 
> > On Wed, 31 Mar 2010 22:36:37 +1100
> > Neil Brown <neilb@suse.de> 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.
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David Miller - March 31, 2010, 9:17 p.m.
From: Neil Brown <neilb@suse.de>
Date: Thu, 1 Apr 2010 07:24:12 +1100

>> --- 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?

That's not how I read the patch, the result is that connect(fd, NULL...)
will now disconnect the socket.
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Neil Brown - March 31, 2010, 10:07 p.m.
On Wed, 31 Mar 2010 14:17:32 -0700 (PDT)
David Miller <davem@davemloft.net> wrote:

> From: Neil Brown <neilb@suse.de>
> Date: Thu, 1 Apr 2010 07:24:12 +1100
> 
> >> --- 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?
> 
> That's not how I read the patch, the result is that connect(fd, NULL...)
> will now disconnect the socket.

Yes, you are right - I read it upside-down.  Sorry.

Thanks,
NeilBrown
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Patch

--- 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;