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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>
This commit is contained in:
Eric Dumazet 2015-07-27 11:33:50 +02:00 committed by David S. Miller
parent 865b804244
commit 11c91ef98f
1 changed files with 9 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

16
net/ipv4/arp.c
View File

@ -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;
}