net: fix improper mtu calculation with lwtunnelv5.9.8-exp3ky/pu-5.9.8

3 files changed, 9 insertions, 6 deletions

diff --git a/include/net/ip6_route.h b/include/net/ip6_route.h
index 2a5277758379..a54b2ece5ef7 100644
--- a/include/net/ip6_route.h
+++ b/include/net/ip6_route.h
@@ -326,7 +326,7 @@ static inline unsigned int ip6_dst_mtu_forward(const struct dst_entry *dst)
 		mtu = idev->cnf.mtu6;
 	rcu_read_unlock();
 
-	return mtu;
+	return mtu - lwtunnel_headroom(dst->lwtstate, mtu);
 }
 
 u32 ip6_mtu_from_fib6(const struct fib6_result *res,
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 9bd30fd4de4b..8bd74d5c4a44 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1407,8 +1407,11 @@ u32 ip_mtu_from_fib_result(struct fib_result *res, __be32 daddr)
 	u32 mtu = 0;
 
 	if (dev_net(dev)->ipv4.sysctl_ip_fwd_use_pmtu ||
-	    fi->fib_metrics->metrics[RTAX_LOCK - 1] & (1 << RTAX_MTU))
+	    fi->fib_metrics->metrics[RTAX_LOCK - 1] & (1 << RTAX_MTU)) {
 		mtu = fi->fib_mtu;
+		if (mtu)
+			return mtu;
+	}
 
 	if (likely(!mtu)) {
 		struct fib_nh_exception *fnhe;
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index fb075d9545b9..f7f0e830b596 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -1587,7 +1587,7 @@ static unsigned int fib6_mtu(const struct fib6_result *res)
 	unsigned int mtu;
 
 	if (res->f6i->fib6_pmtu) {
-		mtu = res->f6i->fib6_pmtu;
+		return min_t(unsigned int, res->f6i->fib6_pmtu, IP6_MAX_MTU);
 	} else {
 		struct net_device *dev = nh->fib_nh_dev;
 		struct inet6_dev *idev;
@@ -3095,7 +3095,7 @@ static unsigned int ip6_mtu(const struct dst_entry *dst)
 
 	mtu = dst_metric_raw(dst, RTAX_MTU);
 	if (mtu)
-		goto out;
+		return min_t(unsigned int, mtu, IP6_MAX_MTU);
 
 	mtu = IPV6_MIN_MTU;
 
@@ -3132,12 +3132,12 @@ u32 ip6_mtu_from_fib6(const struct fib6_result *res,
 	if (unlikely(fib6_metric_locked(f6i, RTAX_MTU))) {
 		mtu = f6i->fib6_pmtu;
 		if (mtu)
-			goto out;
+			return mtu;
 	}
 
 	rt = rt6_find_cached_rt(res, daddr, saddr);
 	if (unlikely(rt)) {
-		mtu = dst_metric_raw(&rt->dst, RTAX_MTU);
+		return dst_metric_raw(&rt->dst, RTAX_MTU);
 	} else {
 		struct net_device *dev = nh->fib_nh_dev;