Re: [PATCH 5/7] netlink, pasta: Fetch link-local address from namespace interface once it's up

[David Gibson <david@gibson.dropbear.id.au>]

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On Thu, Aug 15, 2024 at 12:54:27AM +0200, Stefano Brivio wrote:
> As soon as we bring up the interface, the Linux kernel will set up a
> link-local address for it, so we can fetch it and start using right
> away, if we need a link-local address to communicate to the container
> before we see any traffic coming from it.
> 
> Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
> ---
>  netlink.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++
>  netlink.h |  1 +
>  pasta.c   |  7 +++++++
>  3 files changed, 55 insertions(+)
> 
> diff --git a/netlink.c b/netlink.c
> index 4b49de1..3b37087 100644
> --- a/netlink.c
> +++ b/netlink.c
> @@ -836,6 +836,53 @@ int nl_addr_get(int s, unsigned int ifi, sa_family_t af,
>  	return status;
>  }
>  
> +/**
> + * nl_addr_get_ll() - Get first IPv6 link-local address for a given interface
> + * @s:		Netlink socket
> + * @ifi:	Interface index in outer network namespace
> + * @addr:	Link-local address to fill
> + *
> + * Return: 0 on success, negative error code on failure
> + */
> +int nl_addr_get_ll(int s, unsigned int ifi, void *addr)

Given this is explicitly for IPv6, I don't see a reason not to use
(struct in6_addr *addr) for greater type safety.

> +{
> +	struct req_t {
> +		struct nlmsghdr nlh;
> +		struct ifaddrmsg ifa;
> +	} req = {
> +		.ifa.ifa_family		= AF_INET6,
> +		.ifa.ifa_index		= ifi,
> +	};
> +	struct nlmsghdr *nh;
> +	bool found = false;
> +	char buf[NLBUFSIZ];
> +	ssize_t status;
> +	uint32_t seq;
> +
> +	seq = nl_send(s, &req, RTM_GETADDR, NLM_F_DUMP, sizeof(req));
> +	nl_foreach_oftype(nh, status, s, buf, seq, RTM_NEWADDR) {
> +		struct ifaddrmsg *ifa = (struct ifaddrmsg *)NLMSG_DATA(nh);
> +		struct rtattr *rta;
> +		size_t na;
> +
> +		if (ifa->ifa_index != ifi || ifa->ifa_scope != RT_SCOPE_LINK ||
> +		    found)
> +			continue;
> +
> +		for (rta = IFA_RTA(ifa), na = IFA_PAYLOAD(nh); RTA_OK(rta, na);
> +		     rta = RTA_NEXT(rta, na)) {
> +			if (rta->rta_type != IFA_ADDRESS)
> +				continue;
> +
> +			if (!found) {
> +				memcpy(addr, RTA_DATA(rta), RTA_PAYLOAD(rta));
> +				found = true;
> +			}
> +		}
> +	}
> +	return status;
> +}
> +
>  /**
>   * nl_add_set() - Set IP addresses for given interface and address family
>   * @s:		Netlink socket
> diff --git a/netlink.h b/netlink.h
> index 66a44ad..bdfdef0 100644
> --- a/netlink.h
> +++ b/netlink.h
> @@ -19,6 +19,7 @@ int nl_addr_get(int s, unsigned int ifi, sa_family_t af,
>  		void *addr, int *prefix_len, void *addr_l);
>  int nl_addr_set(int s, unsigned int ifi, sa_family_t af,
>  		const void *addr, int prefix_len);
> +int nl_addr_get_ll(int s, unsigned int ifi, void *addr);
>  int nl_addr_set_ll_nodad(int s, unsigned int ifi);
>  int nl_addr_dup(int s_src, unsigned int ifi_src,
>  		int s_dst, unsigned int ifi_dst, sa_family_t af);
> diff --git a/pasta.c b/pasta.c
> index 838bbb3..cebf54f 100644
> --- a/pasta.c
> +++ b/pasta.c
> @@ -340,6 +340,13 @@ void pasta_ns_conf(struct ctx *c)
>  		}
>  
>  		if (c->ifi6) {
> +			rc = nl_addr_get_ll(nl_sock_ns, c->pasta_ifi,
> +					    &c->ip6.addr_ll_seen);
> +			if (rc < 0) {
> +				die("Can't fetch LL address from namespace: %s",
> +				    strerror(-rc));

Again, we can generally cope with not having an addr_ll_seen
initially, so I think a warn() would make more sense.

> +			}
> +
>  			rc = nl_addr_set_ll_nodad(nl_sock_ns, c->pasta_ifi);
>  			if (rc < 0) {
>  				die("Can't disable DAD for LL in namespace: %s",

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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