The scenario is the following: the user uses a raw socket to send an ipv6
packet, destinated to a not-connected network, and specify a connected nh.
Here is the corresponding python script to reproduce this scenario:
import socket
IPPROTO_RAW = 255
send_s = socket.socket(socket.AF_INET6, socket.SOCK_RAW, IPPROTO_RAW)
# scapy
# p = IPv6(src='fd00:100::1', dst='fd00:200::fa')/ICMPv6EchoRequest()
# str(p)
req =
b'`\x00\x00\x00\x00\x08:@\xfd\x00\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01\xfd\x00\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\xfa\x80\x00\x81\xc0\x00\x00\x00\x00'
send_s.sendto(req, ('fd00:175::2', 0, 0, 0))
fd00:175::/64 is a connected route and fd00:200::fa is not a connected
host.
With this scenario, the kernel starts by sending a NS to resolve
fd00:175::2. When it receives the NA, it flushes its queue and try to send
the initial packet. But instead of sending it, it sends another NS to
resolve fd00:200::fa, which obvioulsy fails, thus the packet is dropped. If
the user sends again the packet, it now uses the right nh (fd00:175::2).
The problem is that ip6_dst_lookup_neigh() uses the rt6i_gateway, which is
:: because the associated route is a connected route, thus it uses the dst
addr of the packet. Let's use rt6_nexthop() to choose the right nh.
Note that rt and in6addr_any are const in ip6_dst_lookup_neigh(), thus
let's constify rt6_nexthop() to avoid ugly cast.
Signed-off-by: Nicolas Dichtel <nicolas.dich...@6wind.com>
---
include/net/ip6_route.h | 4 ++--
net/ipv6/ip6_output.c | 2 +-
net/ipv6/route.c | 3 ++-
3 files changed, 5 insertions(+), 4 deletions(-)
diff --git a/include/net/ip6_route.h b/include/net/ip6_route.h
index 4790beaa86e0..ee7405e759ba 100644
--- a/include/net/ip6_route.h
+++ b/include/net/ip6_route.h
@@ -262,8 +262,8 @@ static inline bool ip6_sk_ignore_df(const struct sock *sk)
inet6_sk(sk)->pmtudisc == IPV6_PMTUDISC_OMIT;
}
-static inline struct in6_addr *rt6_nexthop(struct rt6_info *rt,
- struct in6_addr *daddr)
+static inline const struct in6_addr *rt6_nexthop(const struct rt6_info *rt,
+ const struct in6_addr *daddr)
{
if (rt->rt6i_flags & RTF_GATEWAY)
return &rt->rt6i_gateway;
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 834475717110..21efcd02f337 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -59,8 +59,8 @@ static int ip6_finish_output2(struct net *net, struct sock
*sk, struct sk_buff *
{
struct dst_entry *dst = skb_dst(skb);
struct net_device *dev = dst->dev;
+ const struct in6_addr *nexthop;
struct neighbour *neigh;
- struct in6_addr *nexthop;
int ret;
if (ipv6_addr_is_multicast(&ipv6_hdr(skb)->daddr)) {
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 11ad62effd56..b6449bc03f11 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -218,7 +218,8 @@ static struct neighbour *ip6_dst_neigh_lookup(const struct
dst_entry *dst,
{
const struct rt6_info *rt = container_of(dst, struct rt6_info, dst);
- return ip6_neigh_lookup(&rt->rt6i_gateway, dst->dev, skb, daddr);
+ return ip6_neigh_lookup(rt6_nexthop(rt, &in6addr_any),
+ dst->dev, skb, daddr);
}
static void ip6_confirm_neigh(const struct dst_entry *dst, const void *daddr)
--
2.21.0
