Re: git: 417b35a97b76 - main - netinet: Add a sysctl to allow disabling connections to INADDR_ANY

Hey Mark,

When I set the net.inet.ip.connect_inaddr_wild sysctl node to 0 and
try running `nc -vv 0.0.0.0 22` (this VM has sshd enabled), the
below-linked KASSERT fires:

https://cgit.freebsd.org/src/tree/sys/netinet/in_pcb.c#n2304

No KASSERT is tripped on the IPv6 code path--that works fine. Only
IPv4 is impacted.

Thanks,

-- 
Shawn Webb
Cofounder / Security Engineer
HardenedBSD

Tor-ified Signal: +1 303-901-1600 / shawn_webb_opsec.50
https://git.hardenedbsd.org/hardenedbsd/pubkeys/-/raw/master/Shawn_Webb/03A4CBEBB82EA5A67D9F3853FF2E67A277F8E1FA.pub.asc

On Tue, Aug 20, 2024 at 09:34:39PM UTC, Mark Johnston wrote:
> The branch main has been updated by markj:
> 
> URL: https://cgit.FreeBSD.org/src/commit/?id=417b35a97b7669eb0bf417b43e97cccbedbce6f9
> 
> commit 417b35a97b7669eb0bf417b43e97cccbedbce6f9
> Author:     Mark Johnston <markj@FreeBSD.org>
> AuthorDate: 2024-08-20 21:31:57 +0000
> Commit:     Mark Johnston <markj@FreeBSD.org>
> CommitDate: 2024-08-20 21:31:57 +0000
> 
>     netinet: Add a sysctl to allow disabling connections to INADDR_ANY
>     
>     See the discussion in Bugzilla PR 280705 for context.
>     
>     PR:             280705
>     MFC after:      1 week
>     Differential Revision:  https://reviews.freebsd.org/D46259
> ---
>  sys/netinet/in_pcb.c   |  8 +++++++-
>  sys/netinet6/in6_pcb.c | 12 +++++++++++-
>  2 files changed, 18 insertions(+), 2 deletions(-)
> 
> diff --git a/sys/netinet/in_pcb.c b/sys/netinet/in_pcb.c
> index 1a341d421f31..3fc90f1e12c2 100644
> --- a/sys/netinet/in_pcb.c
> +++ b/sys/netinet/in_pcb.c
> @@ -234,6 +234,12 @@ in_pcbhashseed_init(void)
>  VNET_SYSINIT(in_pcbhashseed_init, SI_SUB_PROTO_DOMAIN, SI_ORDER_FIRST,
>      in_pcbhashseed_init, 0);
>  
> +VNET_DEFINE_STATIC(int, connect_inaddr_wild) = 1;
> +#define	V_connect_inaddr_wild	VNET(connect_inaddr_wild)
> +SYSCTL_INT(_net_inet_ip, OID_AUTO, connect_inaddr_wild,
> +    CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(connect_inaddr_wild), 0,
> +    "Allow connecting to INADDR_ANY or INADDR_BROADCAST for connect(2)");
> +
>  static void in_pcbremhash(struct inpcb *);
>  
>  /*
> @@ -1309,7 +1315,7 @@ in_pcbconnect_setup(struct inpcb *inp, struct sockaddr_in *sin,
>  		inp->inp_flowtype = hash_type;
>  	}
>  #endif
> -	if (!CK_STAILQ_EMPTY(&V_in_ifaddrhead)) {
> +	if (V_connect_inaddr_wild && !CK_STAILQ_EMPTY(&V_in_ifaddrhead)) {
>  		/*
>  		 * If the destination address is INADDR_ANY,
>  		 * use the primary local address.
> diff --git a/sys/netinet6/in6_pcb.c b/sys/netinet6/in6_pcb.c
> index e6ec0f24c898..098b4e50483c 100644
> --- a/sys/netinet6/in6_pcb.c
> +++ b/sys/netinet6/in6_pcb.c
> @@ -83,6 +83,7 @@
>  #include <sys/socket.h>
>  #include <sys/socketvar.h>
>  #include <sys/sockio.h>
> +#include <sys/sysctl.h>
>  #include <sys/errno.h>
>  #include <sys/time.h>
>  #include <sys/priv.h>
> @@ -97,6 +98,7 @@
>  #include <net/if_types.h>
>  #include <net/route.h>
>  #include <net/route/nhop.h>
> +#include <net/vnet.h>
>  
>  #include <netinet/in.h>
>  #include <netinet/in_var.h>
> @@ -112,6 +114,14 @@
>  #include <netinet6/in6_fib.h>
>  #include <netinet6/scope6_var.h>
>  
> +SYSCTL_DECL(_net_inet6);
> +SYSCTL_DECL(_net_inet6_ip6);
> +VNET_DEFINE_STATIC(int, connect_in6addr_wild) = 1;
> +#define	V_connect_in6addr_wild	VNET(connect_in6addr_wild)
> +SYSCTL_INT(_net_inet6_ip6, OID_AUTO, connect_in6addr_wild,
> +    CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(connect_in6addr_wild), 0,
> +    "Allow connecting to the unspecified address for connect(2)");
> +
>  int
>  in6_pcbsetport(struct in6_addr *laddr, struct inpcb *inp, struct ucred *cred)
>  {
> @@ -351,7 +361,7 @@ in6_pcbladdr(struct inpcb *inp, struct sockaddr_in6 *sin6,
>  	if ((error = sa6_embedscope(sin6, V_ip6_use_defzone)) != 0)
>  		return(error);
>  
> -	if (!CK_STAILQ_EMPTY(&V_in6_ifaddrhead)) {
> +	if (V_connect_in6addr_wild && !CK_STAILQ_EMPTY(&V_in6_ifaddrhead)) {
>  		/*
>  		 * If the destination address is UNSPECIFIED addr,
>  		 * use the loopback addr, e.g ::1.
>