Re: [PATCH net] ipv6: make DAD fail with enhanced DAD when nonce length differs

[David Miller <davem@davemloft.net>]

From: Sabrina Dubroca <sd@queasysnail.net>
Date: Fri, 13 Jul 2018 17:21:42 +0200

> Commit adc176c54722 ("ipv6 addrconf: Implemented enhanced DAD (RFC7527)")
> added enhanced DAD with a nonce length of 6 bytes. However, RFC7527
> doesn't specify the length of the nonce, other than being 6 + 8*k bytes,
> with integer k >= 0 (RFC3971 5.3.2). The current implementation simply
> assumes that the nonce will always be 6 bytes, but others systems are
> free to choose different sizes.
> 
> If another system sends a nonce of different length but with the same 6
> bytes prefix, it shouldn't be considered as the same nonce. Thus, check
> that the length of the received nonce is the same as the length we sent.
> 
> Ugly scapy test script running on veth0:
> 
> def loop():
>     pkt=sniff(iface="veth0", filter="icmp6", count=1)
>     pkt = pkt[0]
>     b = bytearray(pkt[Raw].load)
>     b[1] += 1
>     b += b'\xde\xad\xbe\xef\xde\xad\xbe\xef'
>     pkt[Raw].load = bytes(b)
>     pkt[IPv6].plen += 8
>     # fixup checksum after modifying the payload
>     pkt[IPv6].payload.cksum -= 0x3b44
>     if pkt[IPv6].payload.cksum < 0:
>         pkt[IPv6].payload.cksum += 0xffff
>     sendp(pkt, iface="veth0")
> 
> This should result in DAD failure for any address added to veth0's peer,
> but is currently ignored.
> 
> Fixes: adc176c54722 ("ipv6 addrconf: Implemented enhanced DAD (RFC7527)")
> Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
> Reviewed-by: Stefano Brivio <sbrivio@redhat.com>

Applied and queued up for -stable, thank you!