netdev - [PATCH 2/2] net/ipv6: ensure ip6_dst_mtu_forward() returns at least IPV6_MIN

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Message-Id: <20201008033102.623894-2-zenczykowski@gmail.com>
Date:   Wed,  7 Oct 2020 20:31:02 -0700
From:   Maciej Żenczykowski <zenczykowski@...il.com>
To:     Maciej Żenczykowski <maze@...gle.com>,
        "David S . Miller" <davem@...emloft.net>
Cc:     Linux Network Development Mailing List <netdev@...r.kernel.org>
Subject: [PATCH 2/2] net/ipv6: ensure ip6_dst_mtu_forward() returns at least IPV6_MIN_MTU

From: Maciej Żenczykowski <maze@...gle.com>

This is basically just a refactor.

But it does affect (a presumably buggy) call site in:
  net/netfilter/nf_flow_table_core.c
  flow_offload_fill_route()

Signed-off-by: Maciej Żenczykowski <maze@...gle.com>
---
 include/net/ip6_route.h | 4 ++--
 net/ipv6/ip6_output.c   | 2 --
 2 files changed, 2 insertions(+), 4 deletions(-)

diff --git a/include/net/ip6_route.h b/include/net/ip6_route.h
index 598415743f46..25c113dd88ea 100644
--- a/include/net/ip6_route.h
+++ b/include/net/ip6_route.h
@@ -313,14 +313,14 @@ static inline unsigned int ip6_dst_mtu_forward(const struct dst_entry *dst)
 	struct inet6_dev *idev;
 	unsigned int mtu = dst_metric_raw(dst, RTAX_MTU);
 	if (mtu)
-		return mtu;
+		return max(mtu, (unsigned)IPV6_MIN_MTU);
 
 	rcu_read_lock();
 	idev = __in6_dev_get(dst->dev);
 	mtu = idev ? idev->cnf.mtu6 : IPV6_MIN_MTU;
 	rcu_read_unlock();
 
-	return mtu;
+	return max(mtu, (unsigned)IPV6_MIN_MTU);
 }
 
 u32 ip6_mtu_from_fib6(const struct fib6_result *res,
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index c78e67d7747f..bc85f92adaf9 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -540,8 +540,6 @@ int ip6_forward(struct sk_buff *skb)
 	}
 
 	mtu = ip6_dst_mtu_forward(dst);
-	if (mtu < IPV6_MIN_MTU)
-		mtu = IPV6_MIN_MTU;
 
 	if (ip6_pkt_too_big(skb, mtu)) {
 		/* Again, force OUTPUT device used as source address */
-- 
2.28.0.806.g8561365e88-goog