From 11c91ef98f37cd743098de26160fffd7f9bd40e1 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Mon, 27 Jul 2015 11:33:50 +0200 Subject: [PATCH] arp: filter NOARP neighbours for SIOCGARP When arp is off on a device, and ioctl(SIOCGARP) is queried, a buggy answer is given with MAC address of the device, instead of the mac address of the destination/gateway. We filter out NUD_NOARP neighbours for /proc/net/arp, we must do the same for SIOCGARP ioctl. Tested: lpaa23:~# ./arp 10.246.7.190 MAC=00:01:e8:22:cb:1d // correct answer lpaa23:~# ip link set dev eth0 arp off lpaa23:~# cat /proc/net/arp # check arp table is now 'empty' IP address HW type Flags HW address Mask Device lpaa23:~# ./arp 10.246.7.190 MAC=00:1a:11:c3:0d:7f // buggy answer before patch (this is eth0 mac) After patch : lpaa23:~# ip link set dev eth0 arp off lpaa23:~# ./arp 10.246.7.190 ioctl(SIOCGARP) failed: No such device or address Signed-off-by: Eric Dumazet Reported-by: Vytautas Valancius Cc: Willem de Bruijn Signed-off-by: David S. Miller --- net/ipv4/arp.c | 16 +++++++++------- 1 file changed, 9 insertions(+), 7 deletions(-) diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c index 933a92820d26..6c8b1fbafce8 100644 --- a/net/ipv4/arp.c +++ b/net/ipv4/arp.c @@ -1017,14 +1017,16 @@ static int arp_req_get(struct arpreq *r, struct net_device *dev) neigh = neigh_lookup(&arp_tbl, &ip, dev); if (neigh) { - read_lock_bh(&neigh->lock); - memcpy(r->arp_ha.sa_data, neigh->ha, dev->addr_len); - r->arp_flags = arp_state_to_flags(neigh); - read_unlock_bh(&neigh->lock); - r->arp_ha.sa_family = dev->type; - strlcpy(r->arp_dev, dev->name, sizeof(r->arp_dev)); + if (!(neigh->nud_state & NUD_NOARP)) { + read_lock_bh(&neigh->lock); + memcpy(r->arp_ha.sa_data, neigh->ha, dev->addr_len); + r->arp_flags = arp_state_to_flags(neigh); + read_unlock_bh(&neigh->lock); + r->arp_ha.sa_family = dev->type; + strlcpy(r->arp_dev, dev->name, sizeof(r->arp_dev)); + err = 0; + } neigh_release(neigh); - err = 0; } return err; }