ipv4: ipv4_default_advmss() should use route mtu

edumazet · davem330 · commit 164a5e7ad531 · 2017-10-21T01:55:05.000+01:00
ipv4_default_advmss() incorrectly uses the device MTU instead
of the route provided one. IPv6 has the proper behavior,
lets harmonize the two protocols.

Signed-off-by: Eric Dumazet &lt;edumazet@google.com&gt;
Signed-off-by: David S. Miller &lt;davem@davemloft.net&gt;
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
@@ -1250,7 +1250,7 @@ static void set_class_tag(struct rtable *rt, u32 tag)
 static unsigned int ipv4_default_advmss(const struct dst_entry *dst)
 {
 	unsigned int header_size = sizeof(struct tcphdr) + sizeof(struct iphdr);
-	unsigned int advmss = max_t(unsigned int, dst->dev->mtu - header_size,
+	unsigned int advmss = max_t(unsigned int, ipv4_mtu(dst) - header_size,
 				    ip_rt_min_advmss);
 
 	return min(advmss, IPV4_MAX_PMTU - header_size);

Original file line number	Diff line number	Diff line change
`@@ -1250,7 +1250,7 @@ static void set_class_tag(struct rtable *rt, u32 tag)`
`1250`	`1250`	`static unsigned int ipv4_default_advmss(const struct dst_entry *dst)`
`1251`	`1251`	`{`
`1252`	`1252`	`unsigned int header_size = sizeof(struct tcphdr) + sizeof(struct iphdr);`
`1253`		`- unsigned int advmss = max_t(unsigned int, dst->dev->mtu - header_size,`
	`1253`	`+ unsigned int advmss = max_t(unsigned int, ipv4_mtu(dst) - header_size,`
`1254`	`1254`	`ip_rt_min_advmss);`
`1255`	`1255`
`1256`	`1256`	`return min(advmss, IPV4_MAX_PMTU - header_size);`