From 72dcac96c7f8320caf80dfaa559331174060a1ce Mon Sep 17 00:00:00 2001 From: Robert Shearman Date: Thu, 10 Dec 2015 19:30:49 +0000 Subject: [PATCH] mpls: don't dump RTA_VIA attribute if not specified The problem seen is that when adding a route with a nexthop with no via address specified, iproute2 generates bogus output: # ip -f mpls route add 100 dev lo # ip -f mpls route list 100 via inet 0.0.8.0 dev lo The reason for this is that the kernel generates an RTA_VIA attribute with the family set to AF_INET, but the via address data having zero length. The cause of family being AF_INET is that on route insert cfg->rc_via_table is left set to 0, which just happens to be NEIGH_ARP_TABLE which is then translated into AF_INET. iproute2 doesn't validate the length prior to printing and so prints garbage. Although it could be fixed to do the validation, I would argue that AF_INET addresses should always be exactly 4 bytes so the kernel is really giving userspace bogus data. Therefore, avoid generating the RTA_VIA attribute when dumping the route if the via address wasn't specified on add/modify. This is indicated by NEIGH_ARP_TABLE and a zero via address length - if the user specified a via address the address length would have been validated such that it was 4 bytes. Although this is a change in behaviour that is visible to userspace, I believe that what was generated before was invalid and as such userspace wouldn't be expecting it. Signed-off-by: Robert Shearman Signed-off-by: David S. Miller --- net/mpls/af_mpls.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/net/mpls/af_mpls.c b/net/mpls/af_mpls.c index 3be29cb1f658..ac1c116abaac 100644 --- a/net/mpls/af_mpls.c +++ b/net/mpls/af_mpls.c @@ -1235,7 +1235,9 @@ static int mpls_dump_route(struct sk_buff *skb, u32 portid, u32 seq, int event, nla_put_labels(skb, RTA_NEWDST, nh->nh_labels, nh->nh_label)) goto nla_put_failure; - if (nla_put_via(skb, nh->nh_via_table, mpls_nh_via(rt, nh), + if ((nh->nh_via_table != NEIGH_ARP_TABLE || + nh->nh_via_alen != 0) && + nla_put_via(skb, nh->nh_via_table, mpls_nh_via(rt, nh), nh->nh_via_alen)) goto nla_put_failure; dev = rtnl_dereference(nh->nh_dev); @@ -1323,7 +1325,9 @@ static inline size_t lfib_nlmsg_size(struct mpls_route *rt) if (nh->nh_dev) payload += nla_total_size(4); /* RTA_OIF */ - payload += nla_total_size(2 + nh->nh_via_alen); /* RTA_VIA */ + if (nh->nh_via_table != NEIGH_ARP_TABLE || + nh->nh_via_alen != 0) /* RTA_VIA */ + payload += nla_total_size(2 + nh->nh_via_alen); if (nh->nh_labels) /* RTA_NEWDST */ payload += nla_total_size(nh->nh_labels * 4); } else {