Re: [PATCH net] net: ipv6: Fix a bug in ndisc_send_ns when netdev only has a global address

[David Ahern <dsahern@gmail.com>]

On 7/28/19 8:49 PM, Su Yanjun wrote:
> When we send mpls packets and the interface only has a
> manual global ipv6 address, then the two hosts cant communicate.
> I find that in ndisc_send_ns it only tries to get a ll address.
> In my case, the executive path is as below.
> ip6_output
>  ->ip6_finish_output
>   ->lwtunnel_xmit
>    ->mpls_xmit
>     ->neigh_resolve_output
>      ->neigh_probe
>       ->ndisc_solicit
>        ->ndisc_send_ns

for the archives, this is not an MPLS problem but a general IPv6
forwarding problem when the egress interface does not have a link local
address.

> 
> In RFC4861, 7.2.2 says
> "If the source address of the packet prompting the solicitation is the
> same as one of the addresses assigned to the outgoing interface, that
> address SHOULD be placed in the IP Source Address of the outgoing
> solicitation.  Otherwise, any one of the addresses assigned to the
> interface should be used."
> 
> In this patch we try get a global address if we get ll address failed.
> 
> Signed-off-by: Su Yanjun <suyj.fnst@cn.fujitsu.com>
> ---
>  include/net/addrconf.h |  4 ++++
>  net/ipv6/addrconf.c    | 34 ++++++++++++++++++++++++++++++++++
>  net/ipv6/ndisc.c       |  8 ++++++--
>  3 files changed, 44 insertions(+), 2 deletions(-)
> 
> diff --git a/include/net/addrconf.h b/include/net/addrconf.h
> index becdad5..006db8e 100644
> --- a/include/net/addrconf.h
> +++ b/include/net/addrconf.h
> @@ -107,6 +107,10 @@ int __ipv6_get_lladdr(struct inet6_dev *idev, struct in6_addr *addr,
>  		      u32 banned_flags);
>  int ipv6_get_lladdr(struct net_device *dev, struct in6_addr *addr,
>  		    u32 banned_flags);
> +int __ipv6_get_addr(struct inet6_dev *idev, struct in6_addr *addr,
> +		      u32 banned_flags);

no reason to export __ipv6_get_addr. I suspect you copied
__ipv6_get_lladdr but it has an external (to addrconf.c) user. In this
case only ipv6_get_addr needs to be exported.


> +int ipv6_get_addr(struct net_device *dev, struct in6_addr *addr,
> +		    u32 banned_flags);
>  bool inet_rcv_saddr_equal(const struct sock *sk, const struct sock *sk2,
>  			  bool match_wildcard);
>  bool inet_rcv_saddr_any(const struct sock *sk);
> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> index 521e320..4c0a43f 100644
> --- a/net/ipv6/addrconf.c
> +++ b/net/ipv6/addrconf.c
> @@ -1870,6 +1870,40 @@ int ipv6_get_lladdr(struct net_device *dev, struct in6_addr *addr,
>  	return err;
>  }
>  
> +int __ipv6_get_addr(struct inet6_dev *idev, struct in6_addr *addr,
> +		    u32 banned_flags)
> +{
> +	struct inet6_ifaddr *ifp;
> +	int err = -EADDRNOTAVAIL;
> +
> +	list_for_each_entry_reverse(ifp, &idev->addr_list, if_list) {

Addresses are ordered by scope. __ipv6_get_lladdr uses
list_for_each_entry_reverse because the LLA's are after the globals.
Since this is falling back to 'give an address' from this interface, I
think you can just use list_for_each_entry.


> +		if (ifp->scope == 0 &&
> +		    !(ifp->flags & banned_flags)) {
> +			*addr = ifp->addr;
> +			err = 0;
> +			break;
> +		}
> +	}
> +	return err;
> +}
> +
> +int ipv6_get_addr(struct net_device *dev, struct in6_addr *addr,
> +		  u32 banned_flags)
> +{
> +	struct inet6_dev *idev;
> +	int err = -EADDRNOTAVAIL;
> +
> +	rcu_read_lock();
> +	idev = __in6_dev_get(dev);
> +	if (idev) {
> +		read_lock_bh(&idev->lock);
> +		err = __ipv6_get_addr(idev, addr, banned_flags);
> +		read_unlock_bh(&idev->lock);
> +	}
> +	rcu_read_unlock();
> +	return err;
> +}
> +
>  static int ipv6_count_addresses(const struct inet6_dev *idev)
>  {
>  	const struct inet6_ifaddr *ifp;
> diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
> index 083cc1c..18ac2fb 100644
> --- a/net/ipv6/ndisc.c
> +++ b/net/ipv6/ndisc.c
> @@ -606,8 +606,12 @@ void ndisc_send_ns(struct net_device *dev, const struct in6_addr *solicit,
>  
>  	if (!saddr) {

And since you are going to do a v2, another nit - define a local banned
flags and use it for both lookups just to make it clear.

		u32 banned_flags = IFA_F_TENTATIVE | IFA_F_OPTIMISTIC;

>  		if (ipv6_get_lladdr(dev, &addr_buf,
> -				   (IFA_F_TENTATIVE|IFA_F_OPTIMISTIC)))
> -			return;
> +				   (IFA_F_TENTATIVE | IFA_F_OPTIMISTIC))) {
> +			/* try global address */
> +			if (ipv6_get_addr(dev, &addr_buf,
> +					  (IFA_F_TENTATIVE | IFA_F_OPTIMISTIC)))
> +				return;
> +		}
>  		saddr = &addr_buf;
>  	}
>  
>