4.17-stable review patch. If anyone has any objections, please let me know.
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From: Sabrina Dubroca sd@queasysnail.net
[ Upstream commit e66515999b627368892ccc9b3a13a506f2ea1357 ]
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 Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/ipv6/ndisc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/net/ipv6/ndisc.c +++ b/net/ipv6/ndisc.c @@ -811,7 +811,7 @@ static void ndisc_recv_ns(struct sk_buff return; } } - if (ndopts.nd_opts_nonce) + if (ndopts.nd_opts_nonce && ndopts.nd_opts_nonce->nd_opt_len == 1) memcpy(&nonce, (u8 *)(ndopts.nd_opts_nonce + 1), 6);
inc = ipv6_addr_is_multicast(daddr);