From: Mathieu Desnoyers mathieu.desnoyers@efficios.com
[ Upstream commit 272928d1cdacfc3b55f605cb0e9115832ecfb20c ]
As per RFC4443, the destination address field for ICMPv6 error messages is copied from the source address field of the invoking packet.
In configurations with Virtual Routing and Forwarding tables, looking up which routing table to use for sending ICMPv6 error messages is currently done by using the destination net_device.
If the source and destination interfaces are within separate VRFs, or one in the global routing table and the other in a VRF, looking up the source address of the invoking packet in the destination interface's routing table will fail if the destination interface's routing table contains no route to the invoking packet's source address.
One observable effect of this issue is that traceroute6 does not work in the following cases:
- Route leaking between global routing table and VRF - Route leaking between VRFs
Use the source device routing table when sending ICMPv6 error messages.
[ In the context of ipv4, it has been pointed out that a similar issue may exist with ICMP errors triggered when forwarding between network namespaces. It would be worthwhile to investigate whether ipv6 has similar issues, but is outside of the scope of this investigation. ]
[ Testing shows that similar issues exist with ipv6 unreachable / fragmentation needed messages. However, investigation of this additional failure mode is beyond this investigation's scope. ]
Link: https://tools.ietf.org/html/rfc4443 Signed-off-by: Mathieu Desnoyers mathieu.desnoyers@efficios.com Reviewed-by: David Ahern dsahern@gmail.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- net/ipv6/icmp.c | 7 +++++-- net/ipv6/ip6_output.c | 2 -- 2 files changed, 5 insertions(+), 4 deletions(-)
diff --git a/net/ipv6/icmp.c b/net/ipv6/icmp.c index c5f2b17b7ee1a..36c29df70fb6e 100644 --- a/net/ipv6/icmp.c +++ b/net/ipv6/icmp.c @@ -481,8 +481,11 @@ static void icmp6_send(struct sk_buff *skb, u8 type, u8 code, __u32 info, if (__ipv6_addr_needs_scope_id(addr_type)) { iif = icmp6_iif(skb); } else { - dst = skb_dst(skb); - iif = l3mdev_master_ifindex(dst ? dst->dev : skb->dev); + /* + * The source device is used for looking up which routing table + * to use for sending an ICMP error. + */ + iif = l3mdev_master_ifindex(skb->dev); }
/* diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c index 5198bc1232045..140fffe5358ba 100644 --- a/net/ipv6/ip6_output.c +++ b/net/ipv6/ip6_output.c @@ -470,8 +470,6 @@ int ip6_forward(struct sk_buff *skb) * check and decrement ttl */ if (hdr->hop_limit <= 1) { - /* Force OUTPUT device used as source address */ - skb->dev = dst->dev; icmpv6_send(skb, ICMPV6_TIME_EXCEED, ICMPV6_EXC_HOPLIMIT, 0); __IP6_INC_STATS(net, ip6_dst_idev(dst), IPSTATS_MIB_INHDRERRORS);