[PATCH 4.20 180/183] netfilter: ipv6: Dont preserve original oif for loopback address

From: Greg Kroah-Hartman
Date: Mon Feb 25 2019 - 16:38:00 EST

4.20-stable review patch. If anyone has any objections, please let me know.


From: Eli Cooper <elicooper@xxxxxxx>

commit 15df03c661cb362366ecfc3a21820cb934f3e4ca upstream.

Commit 508b09046c0f ("netfilter: ipv6: Preserve link scope traffic
original oif") made ip6_route_me_harder() keep the original oif for
link-local and multicast packets. However, it also affected packets
for the loopback address because it used rt6_need_strict().

REDIRECT rules in the OUTPUT chain rewrite the destination to loopback
address; thus its oif should not be preserved. This commit fixes the bug
that redirected local packets are being dropped. Actually the packet was
not exactly dropped; Instead it was sent out to the original oif rather
than lo. When a packet with daddr ::1 is sent to the router, it is
effectively dropped.

Fixes: 508b09046c0f ("netfilter: ipv6: Preserve link scope traffic original oif")
Signed-off-by: Eli Cooper <elicooper@xxxxxxx>
Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

net/ipv6/netfilter.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

--- a/net/ipv6/netfilter.c
+++ b/net/ipv6/netfilter.c
@@ -23,9 +23,11 @@ int ip6_route_me_harder(struct net *net,
struct sock *sk = sk_to_full_sk(skb->sk);
unsigned int hh_len;
struct dst_entry *dst;
+ int strict = (ipv6_addr_type(&iph->daddr) &
struct flowi6 fl6 = {
.flowi6_oif = sk && sk->sk_bound_dev_if ? sk->sk_bound_dev_if :
- rt6_need_strict(&iph->daddr) ? skb_dst(skb)->dev->ifindex : 0,
+ strict ? skb_dst(skb)->dev->ifindex : 0,
.flowi6_mark = skb->mark,
.flowi6_uid = sock_net_uid(net, sk),
.daddr = iph->daddr,