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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Eli Cooper <elicooper@gmx.com>,
        Pablo Neira Ayuso <pablo@netfilter.org>
Subject: [PATCH 4.20 180/183] netfilter: ipv6: Dont preserve original oif for loopback address
Date:   Mon, 25 Feb 2019 22:12:33 +0100
Message-Id: <20190225195125.477175237@linuxfoundation.org>
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4.20-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eli Cooper <elicooper@gmx.com>

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@gmx.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 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) &
+		      (IPV6_ADDR_MULTICAST | IPV6_ADDR_LINKLOCAL));
 	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,