From 0c51e12e218f20b7d976158fdc18019627326f7a Mon Sep 17 00:00:00 2001 From: Ido Schimmel Date: Sat, 19 Feb 2022 17:45:19 +0200 Subject: ipv4: Invalidate neighbour for broadcast address upon address addition In case user space sends a packet destined to a broadcast address when a matching broadcast route is not configured, the kernel will create a unicast neighbour entry that will never be resolved [1]. When the broadcast route is configured, the unicast neighbour entry will not be invalidated and continue to linger, resulting in packets being dropped. Solve this by invalidating unresolved neighbour entries for broadcast addresses after routes for these addresses are internally configured by the kernel. This allows the kernel to create a broadcast neighbour entry following the next route lookup. Another possible solution that is more generic but also more complex is to have the ARP code register a listener to the FIB notification chain and invalidate matching neighbour entries upon the addition of broadcast routes. It is also possible to wave off the issue as a user space problem, but it seems a bit excessive to expect user space to be that intimately familiar with the inner workings of the FIB/neighbour kernel code. [1] https://lore.kernel.org/netdev/55a04a8f-56f3-f73c-2aea-2195923f09d1@huawei.com/ Reported-by: Wang Hai Signed-off-by: Ido Schimmel Tested-by: Wang Hai Signed-off-by: David S. Miller --- net/ipv4/arp.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) (limited to 'net/ipv4/arp.c') diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c index 4db0325f6e1a..dc28f0588e54 100644 --- a/net/ipv4/arp.c +++ b/net/ipv4/arp.c @@ -1116,13 +1116,18 @@ static int arp_req_get(struct arpreq *r, struct net_device *dev) return err; } -static int arp_invalidate(struct net_device *dev, __be32 ip) +int arp_invalidate(struct net_device *dev, __be32 ip, bool force) { struct neighbour *neigh = neigh_lookup(&arp_tbl, &ip, dev); int err = -ENXIO; struct neigh_table *tbl = &arp_tbl; if (neigh) { + if ((neigh->nud_state & NUD_VALID) && !force) { + neigh_release(neigh); + return 0; + } + if (neigh->nud_state & ~NUD_NOARP) err = neigh_update(neigh, NULL, NUD_FAILED, NEIGH_UPDATE_F_OVERRIDE| @@ -1169,7 +1174,7 @@ static int arp_req_delete(struct net *net, struct arpreq *r, if (!dev) return -EINVAL; } - return arp_invalidate(dev, ip); + return arp_invalidate(dev, ip, true); } /* -- cgit v1.2.3