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SubjectRe: patch: support long (above 14 bytes) HW addresses in arp_ioctl
Date
[netdev added to cc list]

> In arp_req_get() in net/arp.c, there is code:
>
> memcpy(r->arp_ha.sa_data, neigh->ha, dev->addr_len);
>
> dev->addr_len can be larger than size of
> r->arp_ha.sa_data. Inititally, I thought it would corrupt kernel
> stack. I was wrong, since r still has enough space not to overflow
> even for the largest HW address (32 bytes). It would corrupt the data
> structure though, and that corrupted reply would be propagated to
> user.
>
> There is a similar situation in arp_req_set(), where a "junk" arp
> entry will be set if dev->addr_len is larger that 14 bytes.
>
> At the very minimum, both arp_req_set() and arp_req_get() should
> return error (-EINVAL), and not return junk or set junk. Truncated
> /proc/net/arp output should also be fixed.

The EINVAL return makes sense; I'm not sure /proc/net/arp is important
enough to fix. I guess it depends on the impact of the fix.

> I was not aware that rtnetlink is capable of doing things like arp
> table or interface manipulation (like netdevice ioctls). My
> applications needs to be able to manipulate arp cache for large macs,
> and I do not mind recompiling by adding a flag. I do not mind fixing
> arp cli to use this either (venerable arp does use arp_ioctl). And
> there are many many legacy solutions that use arp_ioctl() in programs
> and arp utility in scripts. Consider porting those to infiniband.
>
> Will rtnetlink work for any net_device (like netdevice ioctls do) for
> ARP and interface configurations calls or does it require special
> support in net_device itself? Any possible problems with rtnetlink?

rtnetlink is the preferred modern interface between userspace and kernel
for networking information. There is also the "iproute2" package that
provides a good command line interface that is capable of handling IPoIB
addresses. For example:

$ ip addr show dev ib1
5: ib1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 2044 qdisc pfifo_fast state UP qlen 256
link/infiniband 80:00:00:48:fe:80:00:00:00:00:00:00:00:02:c9:03:00:00:01:65 brd 00:ff:ff:ff:ff:12:40:1b:ff:ff:00:00:00:00:00:00:ff:ff:ff:ff
inet 192.168.145.74/24 brd 192.168.145.255 scope global ib1
inet6 fe80::202:c903:0:165/64 scope link
valid_lft forever preferred_lft forever

$ ip neigh
192.168.145.73 dev ib1 lladdr 80:00:00:48:fe:80:00:00:00:00:00:00:00:02:c9:03:00:00:01:30 STALE
172.29.224.1 dev eth0 lladdr 00:00:0c:07:ac:e0 REACHABLE

and so on.

- R.


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