[PATCH net-next v2 1/2] l2tp: account for IP version in SKB headroom

[PATCH net-next v2 1/2] l2tp: account for IP version in SKB headroom

[David Bauer]

Account for the IP version of the tunnel when accounting skb headroom on
xmit. This avoids having to potentially copy the skb a second time down
the stack due to allocating not enough space for IPv6 headers in case
the tunnel uses IPv6.

Signed-off-by: David Bauer <mail@david-bauer.net>
---
 net/l2tp/l2tp_core.c | 3 ++-
 net/l2tp/l2tp_core.h | 1 +
 net/l2tp/l2tp_eth.c  | 9 ++-------
 3 files changed, 5 insertions(+), 8 deletions(-)

diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index 4712cc41881a3..d6fa0f7436629 100644
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -1237,7 +1237,7 @@ static int l2tp_xmit_core(struct l2tp_session *session, struct sk_buff *skb, uns
 	 * make room. Adjust truesize.
 	 */
 	uhlen = (tunnel->encap == L2TP_ENCAPTYPE_UDP) ? sizeof(*uh) : 0;
-	headroom = NET_SKB_PAD + sizeof(struct iphdr) + uhlen + session->hdr_len;
+	headroom = NET_SKB_PAD + tunnel->l3_overhead + uhlen + session->hdr_len;
 	if (skb_cow_head(skb, headroom)) {
 		kfree_skb(skb);
 		return NET_XMIT_DROP;
@@ -1688,6 +1688,7 @@ int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, struct net *net,
 	}
 
 	sk->sk_allocation = GFP_ATOMIC;
+	tunnel->l3_overhead = kernel_sock_ip_overhead(sk);
 	release_sock(sk);
 
 	sock_hold(sk);
diff --git a/net/l2tp/l2tp_core.h b/net/l2tp/l2tp_core.h
index ffd8ced3a51ff..aab574376d95f 100644
--- a/net/l2tp/l2tp_core.h
+++ b/net/l2tp/l2tp_core.h
@@ -167,6 +167,7 @@ struct l2tp_tunnel {
 	u32			tunnel_id;
 	u32			peer_tunnel_id;
 	int			version;	/* 2=>L2TPv2, 3=>L2TPv3 */
+	int			l3_overhead;	/* IP header overhead */
 
 	char			name[L2TP_TUNNEL_NAME_MAX]; /* for logging */
 	enum l2tp_encap_type	encap;
diff --git a/net/l2tp/l2tp_eth.c b/net/l2tp/l2tp_eth.c
index a4956ef9574cc..9e5f9deac08cf 100644
--- a/net/l2tp/l2tp_eth.c
+++ b/net/l2tp/l2tp_eth.c
@@ -188,7 +188,6 @@ static void l2tp_eth_adjust_mtu(struct l2tp_tunnel *tunnel,
 				struct net_device *dev)
 {
 	unsigned int overhead = 0;
-	u32 l3_overhead = 0;
 	u32 mtu;
 
 	/* if the encap is UDP, account for UDP header size */
@@ -197,11 +196,7 @@ static void l2tp_eth_adjust_mtu(struct l2tp_tunnel *tunnel,
 		dev->needed_headroom += sizeof(struct udphdr);
 	}
 
-	lock_sock(tunnel->sock);
-	l3_overhead = kernel_sock_ip_overhead(tunnel->sock);
-	release_sock(tunnel->sock);
-
-	if (l3_overhead == 0) {
+	if (tunnel->l3_overhead == 0) {
 		/* L3 Overhead couldn't be identified, this could be
 		 * because tunnel->sock was NULL or the socket's
 		 * address family was not IPv4 or IPv6,
@@ -212,7 +207,7 @@ static void l2tp_eth_adjust_mtu(struct l2tp_tunnel *tunnel,
 	/* Adjust MTU, factor overhead - underlay L3, overlay L2 hdr
 	 * UDP overhead, if any, was already factored in above.
 	 */
-	overhead += session->hdr_len + ETH_HLEN + l3_overhead;
+	overhead += session->hdr_len + ETH_HLEN + tunnel->l3_overhead;
 
 	mtu = l2tp_tunnel_dst_mtu(tunnel) - overhead;
 	if (mtu < dev->min_mtu || mtu > dev->max_mtu)
-- 
2.53.0

[PATCH net-next v2 2/2] l2tp: unify headroom calculation

[David Bauer]

Unify the calculation to determine the required headroom for each skb.
This was previously done inconsistently, resulting requesting more space
in the skb headroom when crafting the L2TP header than indicated with
needed_headroom.

Signed-off-by: David Bauer <mail@david-bauer.net>
---
 net/l2tp/l2tp_core.c |  8 +++-----
 net/l2tp/l2tp_core.h | 18 ++++++++++++++++++
 net/l2tp/l2tp_eth.c  | 14 +++-----------
 3 files changed, 24 insertions(+), 16 deletions(-)

diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index d6fa0f7436629..73361c46e6782 100644
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -1227,18 +1227,16 @@ static int l2tp_xmit_core(struct l2tp_session *session, struct sk_buff *skb, uns
 	struct l2tp_tunnel *tunnel = session->tunnel;
 	unsigned int data_len = skb->len;
 	struct sock *sk = tunnel->sock;
-	int headroom, uhlen, udp_len;
 	int ret = NET_XMIT_SUCCESS;
 	struct inet_sock *inet;
 	struct udphdr *uh;
+	int udp_len;
 
 	/* Check that there's enough headroom in the skb to insert IP,
 	 * UDP and L2TP headers. If not enough, expand it to
 	 * make room. Adjust truesize.
 	 */
-	uhlen = (tunnel->encap == L2TP_ENCAPTYPE_UDP) ? sizeof(*uh) : 0;
-	headroom = NET_SKB_PAD + tunnel->l3_overhead + uhlen + session->hdr_len;
-	if (skb_cow_head(skb, headroom)) {
+	if (skb_cow_head(skb, l2tp_session_skb_headroom(session, tunnel))) {
 		kfree_skb(skb);
 		return NET_XMIT_DROP;
 	}
@@ -1290,7 +1288,7 @@ static int l2tp_xmit_core(struct l2tp_session *session, struct sk_buff *skb, uns
 		uh = udp_hdr(skb);
 		uh->source = inet->inet_sport;
 		uh->dest = inet->inet_dport;
-		udp_len = uhlen + session->hdr_len + data_len;
+		udp_len = l2tp_tunnel_udp_hdrlen(tunnel) + session->hdr_len + data_len;
 		if (udp_len > U16_MAX) {
 			kfree_skb(skb);
 			ret = NET_XMIT_DROP;
diff --git a/net/l2tp/l2tp_core.h b/net/l2tp/l2tp_core.h
index aab574376d95f..9f24045695b61 100644
--- a/net/l2tp/l2tp_core.h
+++ b/net/l2tp/l2tp_core.h
@@ -335,6 +335,24 @@ static inline int l2tp_v3_ensure_opt_in_linear(struct l2tp_session *session, str
 	return 0;
 }
 
+static inline int l2tp_tunnel_udp_hdrlen(struct l2tp_tunnel *tunnel)
+{
+	return tunnel->encap == L2TP_ENCAPTYPE_UDP ?
+		sizeof(struct udphdr) : 0;
+}
+
+static inline int l2tp_session_overhead(struct l2tp_session *session, struct l2tp_tunnel *tunnel)
+{
+	return l2tp_tunnel_udp_hdrlen(tunnel) + session->hdr_len +
+		tunnel->l3_overhead;
+}
+
+static inline int l2tp_session_skb_headroom(struct l2tp_session *session,
+					    struct l2tp_tunnel *tunnel)
+{
+	return NET_SKB_PAD + l2tp_session_overhead(session, tunnel);
+}
+
 #define MODULE_ALIAS_L2TP_PWTYPE(type) \
 	MODULE_ALIAS("net-l2tp-type-" __stringify(type))
 
diff --git a/net/l2tp/l2tp_eth.c b/net/l2tp/l2tp_eth.c
index 9e5f9deac08cf..6f4516180c922 100644
--- a/net/l2tp/l2tp_eth.c
+++ b/net/l2tp/l2tp_eth.c
@@ -190,12 +190,6 @@ static void l2tp_eth_adjust_mtu(struct l2tp_tunnel *tunnel,
 	unsigned int overhead = 0;
 	u32 mtu;
 
-	/* if the encap is UDP, account for UDP header size */
-	if (tunnel->encap == L2TP_ENCAPTYPE_UDP) {
-		overhead += sizeof(struct udphdr);
-		dev->needed_headroom += sizeof(struct udphdr);
-	}
-
 	if (tunnel->l3_overhead == 0) {
 		/* L3 Overhead couldn't be identified, this could be
 		 * because tunnel->sock was NULL or the socket's
@@ -204,10 +198,8 @@ static void l2tp_eth_adjust_mtu(struct l2tp_tunnel *tunnel,
 		 */
 		return;
 	}
-	/* Adjust MTU, factor overhead - underlay L3, overlay L2 hdr
-	 * UDP overhead, if any, was already factored in above.
-	 */
-	overhead += session->hdr_len + ETH_HLEN + tunnel->l3_overhead;
+	/* Calculate required overhead */
+	overhead = ETH_HLEN + l2tp_session_overhead(session, tunnel);
 
 	mtu = l2tp_tunnel_dst_mtu(tunnel) - overhead;
 	if (mtu < dev->min_mtu || mtu > dev->max_mtu)
@@ -215,7 +207,7 @@ static void l2tp_eth_adjust_mtu(struct l2tp_tunnel *tunnel,
 	else
 		dev->mtu = mtu;
 
-	dev->needed_headroom += session->hdr_len;
+	dev->needed_headroom = l2tp_session_skb_headroom(session, tunnel);
 }
 
 static int l2tp_eth_create(struct net *net, struct l2tp_tunnel *tunnel,
-- 
2.53.0