Commit 11c91ef9 authored Jul 27, 2015 by Eric Dumazet Committed by David S. Miller Jul 28, 2015

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 <edumazet@google.com>
Reported-by: Vytautas Valancius <valas@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 865b8042

net/ipv4/arp.c

+9 −7

Original line number	Original line	Diff line number	Diff line
	@@ -1017,15 +1017,17 @@ static int arp_req_get(struct arpreq r, struct net_device dev)

	neigh = neigh_lookup(&arp_tbl, &ip, dev);		neigh = neigh_lookup(&arp_tbl, &ip, dev);
	if (neigh) {		if (neigh) {
			if (!(neigh->nud_state & NUD_NOARP)) {
	read_lock_bh(&neigh->lock);		read_lock_bh(&neigh->lock);
	memcpy(r->arp_ha.sa_data, neigh->ha, dev->addr_len);		memcpy(r->arp_ha.sa_data, neigh->ha, dev->addr_len);
	r->arp_flags = arp_state_to_flags(neigh);		r->arp_flags = arp_state_to_flags(neigh);
	read_unlock_bh(&neigh->lock);		read_unlock_bh(&neigh->lock);
	r->arp_ha.sa_family = dev->type;		r->arp_ha.sa_family = dev->type;
	strlcpy(r->arp_dev, dev->name, sizeof(r->arp_dev));		strlcpy(r->arp_dev, dev->name, sizeof(r->arp_dev));
	neigh_release(neigh);
	err = 0;		err = 0;
	}		}
			neigh_release(neigh);
			}
	return err;		return err;
	}		}