[PATCH bpf-next] net: core: Fix build with CONFIG_IPV6=m

[PATCH bpf-next] net: core: Fix build with CONFIG_IPV6=m

[Joe Stringer]

Stephen Rothwell reports the following link failure with IPv6 as module:

  x86_64-linux-gnu-ld: net/core/filter.o: in function `sk_lookup':
  (.text+0x19219): undefined reference to `__udp6_lib_lookup'

Fix the build by only enabling the IPv6 socket lookup if IPv6 support is
compiled into the kernel.

Signed-off-by: Joe Stringer <joe@wand.net.nz>
---
 net/core/filter.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index 591c698bc517..30c6b2d3ef16 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -4838,7 +4838,7 @@ struct sock *sk_lookup(struct net *net, struct bpf_sock_tuple *tuple,
 			sk = __udp4_lib_lookup(net, src4, tuple->ipv4.sport,
 					       dst4, tuple->ipv4.dport,
 					       dif, sdif, &udp_table, skb);
-#if IS_ENABLED(CONFIG_IPV6)
+#if IS_REACHABLE(CONFIG_IPV6)
 	} else {
 		struct in6_addr *src6 = (struct in6_addr *)&tuple->ipv6.saddr;
 		struct in6_addr *dst6 = (struct in6_addr *)&tuple->ipv6.daddr;
-- 
2.17.1

Re: [PATCH bpf-next] net: core: Fix build with CONFIG_IPV6=m

[Daniel Borkmann]

On 10/03/2018 07:32 AM, Joe Stringer wrote:
> Stephen Rothwell reports the following link failure with IPv6 as module:
> 
>   x86_64-linux-gnu-ld: net/core/filter.o: in function `sk_lookup':
>   (.text+0x19219): undefined reference to `__udp6_lib_lookup'
> 
> Fix the build by only enabling the IPv6 socket lookup if IPv6 support is
> compiled into the kernel.
> 
> Signed-off-by: Joe Stringer <joe@wand.net.nz>
> ---
>  net/core/filter.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 591c698bc517..30c6b2d3ef16 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -4838,7 +4838,7 @@ struct sock *sk_lookup(struct net *net, struct bpf_sock_tuple *tuple,
>  			sk = __udp4_lib_lookup(net, src4, tuple->ipv4.sport,
>  					       dst4, tuple->ipv4.dport,
>  					       dif, sdif, &udp_table, skb);
> -#if IS_ENABLED(CONFIG_IPV6)
> +#if IS_REACHABLE(CONFIG_IPV6)
>  	} else {
>  		struct in6_addr *src6 = (struct in6_addr *)&tuple->ipv6.saddr;
>  		struct in6_addr *dst6 = (struct in6_addr *)&tuple->ipv6.daddr;
> 

Applied as a quick fix, thanks Joe, but ideally this should also work when ipv6
is compiled as a module. There's the ipv6_bpf_stub, which does that job for other
helpers that would call into v6 code out of the builtin filter.c, so I think we
should follow the same approach here as well. See commit d74bad4e74ee ("bpf:
Hooks for sys_connect").

Thanks,
Daniel

Re: [PATCH bpf-next] net: core: Fix build with CONFIG_IPV6=m

[Joe Stringer]

On Thu, 4 Oct 2018 at 01:48, Daniel Borkmann <daniel@iogearbox.net> wrote:
>
> On 10/03/2018 07:32 AM, Joe Stringer wrote:
> > Stephen Rothwell reports the following link failure with IPv6 as module:
> >
> >   x86_64-linux-gnu-ld: net/core/filter.o: in function `sk_lookup':
> >   (.text+0x19219): undefined reference to `__udp6_lib_lookup'
> >
> > Fix the build by only enabling the IPv6 socket lookup if IPv6 support is
> > compiled into the kernel.
> >
> > Signed-off-by: Joe Stringer <joe@wand.net.nz>
> > ---
> >  net/core/filter.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/net/core/filter.c b/net/core/filter.c
> > index 591c698bc517..30c6b2d3ef16 100644
> > --- a/net/core/filter.c
> > +++ b/net/core/filter.c
> > @@ -4838,7 +4838,7 @@ struct sock *sk_lookup(struct net *net, struct bpf_sock_tuple *tuple,
> >                       sk = __udp4_lib_lookup(net, src4, tuple->ipv4.sport,
> >                                              dst4, tuple->ipv4.dport,
> >                                              dif, sdif, &udp_table, skb);
> > -#if IS_ENABLED(CONFIG_IPV6)
> > +#if IS_REACHABLE(CONFIG_IPV6)
> >       } else {
> >               struct in6_addr *src6 = (struct in6_addr *)&tuple->ipv6.saddr;
> >               struct in6_addr *dst6 = (struct in6_addr *)&tuple->ipv6.daddr;
> >
>
> Applied as a quick fix, thanks Joe, but ideally this should also work when ipv6
> is compiled as a module. There's the ipv6_bpf_stub, which does that job for other
> helpers that would call into v6 code out of the builtin filter.c, so I think we
> should follow the same approach here as well. See commit d74bad4e74ee ("bpf:
> Hooks for sys_connect").

Thanks for the pointers, I'll look into that.

To confirm my understanding, is it possible to unload the IPv6 module?
I don't see any code that uninitializes "ipv6_bpf_stub". Seems like a
simple conditional check on that variable should be enough to gate its
usage from packet paths where sk_lookup could be invoked (Given that
the system could receive any packets, including IPv6 when the module
is not loaded).

Cheers,
Joe

Re: [PATCH bpf-next] net: core: Fix build with CONFIG_IPV6=m

[Daniel Borkmann]

On 10/04/2018 08:33 PM, Joe Stringer wrote:
> On Thu, 4 Oct 2018 at 01:48, Daniel Borkmann <daniel@iogearbox.net> wrote:
>>
>> On 10/03/2018 07:32 AM, Joe Stringer wrote:
>>> Stephen Rothwell reports the following link failure with IPv6 as module:
>>>
>>>   x86_64-linux-gnu-ld: net/core/filter.o: in function `sk_lookup':
>>>   (.text+0x19219): undefined reference to `__udp6_lib_lookup'
>>>
>>> Fix the build by only enabling the IPv6 socket lookup if IPv6 support is
>>> compiled into the kernel.
>>>
>>> Signed-off-by: Joe Stringer <joe@wand.net.nz>
>>> ---
>>>  net/core/filter.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/net/core/filter.c b/net/core/filter.c
>>> index 591c698bc517..30c6b2d3ef16 100644
>>> --- a/net/core/filter.c
>>> +++ b/net/core/filter.c
>>> @@ -4838,7 +4838,7 @@ struct sock *sk_lookup(struct net *net, struct bpf_sock_tuple *tuple,
>>>                       sk = __udp4_lib_lookup(net, src4, tuple->ipv4.sport,
>>>                                              dst4, tuple->ipv4.dport,
>>>                                              dif, sdif, &udp_table, skb);
>>> -#if IS_ENABLED(CONFIG_IPV6)
>>> +#if IS_REACHABLE(CONFIG_IPV6)
>>>       } else {
>>>               struct in6_addr *src6 = (struct in6_addr *)&tuple->ipv6.saddr;
>>>               struct in6_addr *dst6 = (struct in6_addr *)&tuple->ipv6.daddr;
>>>
>>
>> Applied as a quick fix, thanks Joe, but ideally this should also work when ipv6
>> is compiled as a module. There's the ipv6_bpf_stub, which does that job for other
>> helpers that would call into v6 code out of the builtin filter.c, so I think we
>> should follow the same approach here as well. See commit d74bad4e74ee ("bpf:
>> Hooks for sys_connect").
> 
> Thanks for the pointers, I'll look into that.
> 
> To confirm my understanding, is it possible to unload the IPv6 module?
> I don't see any code that uninitializes "ipv6_bpf_stub". Seems like a
> simple conditional check on that variable should be enough to gate its
> usage from packet paths where sk_lookup could be invoked (Given that
> the system could receive any packets, including IPv6 when the module
> is not loaded).

No unload, this has been removed via 8ce440610357 ("ipv6: do not allow
ipv6 module to be removed").

Thanks,
Daniel