netdev - [PATCH net 2/2] gtp: fix fragmentation needed check with gso

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Message-Id: <20231022202519.659526-3-pablo@netfilter.org>
Date: Sun, 22 Oct 2023 22:25:18 +0200
From: Pablo Neira Ayuso <pablo@...filter.org>
To: netdev@...r.kernel.org
Cc: osmocom-net-gprs@...ts.osmocom.org,
	davem@...emloft.net,
	kuba@...nel.org,
	pabeni@...hat.com,
	edumazet@...gle.com,
	laforge@...ocom.org,
	laforge@...monks.org
Subject: [PATCH net 2/2] gtp: fix fragmentation needed check with gso

Call skb_gso_validate_network_len() to check if packet is over PMTU.

Fixes: 459aa660eb1d ("gtp: add initial driver for datapath of GPRS Tunneling Protocol (GTP-U)")
Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
---
 drivers/net/gtp.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/net/gtp.c b/drivers/net/gtp.c
index 144ec626230d..b22596b18ee8 100644
--- a/drivers/net/gtp.c
+++ b/drivers/net/gtp.c
@@ -872,8 +872,9 @@ static int gtp_build_skb_ip4(struct sk_buff *skb, struct net_device *dev,
 
 	skb_dst_update_pmtu_no_confirm(skb, mtu);
 
-	if (!skb_is_gso(skb) && (iph->frag_off & htons(IP_DF)) &&
-	    mtu < ntohs(iph->tot_len)) {
+	if (iph->frag_off & htons(IP_DF) &&
+	    ((!skb_is_gso(skb) && skb->len > mtu) ||
+	     (skb_is_gso(skb) && !skb_gso_validate_network_len(skb, mtu)))) {
 		netdev_dbg(dev, "packet too big, fragmentation needed\n");
 		icmp_ndo_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED,
 			      htonl(mtu));
-- 
2.30.2