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Patch "ipv4: allow local fragmentation in ip_finish_output_gso()" has been added to the 4.8-stable tree

PATCH [email protected] 1 participant 1 message Nov 18, 2016

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This is a note to let you know that I've just added the patch titled

ipv4: allow local fragmentation in ip_finish_output_gso()

to the 4.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
ipv4-allow-local-fragmentation-in-ip_finish_output_gso.patch
and it can be found in the queue-4.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Quoted 1 line

From foo@baz Fri Nov 18 11:35:46 CET 2016

From: Lance Richardson <[email protected]>
Date: Wed, 2 Nov 2016 16:36:17 -0400
Subject: ipv4: allow local fragmentation in ip_finish_output_gso()

From: Lance Richardson <[email protected]>

[ Upstream commit 9ee6c5dc816aa8256257f2cd4008a9291ec7e985 ]

Some configurations (e.g. geneve interface with default MTU of 1500 over an ethernet interface with 1500 MTU) result in the transmission of packets that exceed the configured MTU. While this should be considered to be a "bad" configuration, it is still allowed and should not result in the sending of packets that exceed the configured MTU.

Fix by dropping the assumption in ip_finish_output_gso() that locally originated gso packets will never need fragmentation. Basic testing using iperf (observing CPU usage and bandwidth) have shown no measurable performance impact for traffic not requiring fragmentation.

Fixes c7ba65d7b649 ("net: ip: push gso skb forwarding handling down the stack")
Reported-by Jan Tluka <[email protected]>
Signed-off-by Lance Richardson <[email protected]>
Acked-by Hannes Frederic Sowa <[email protected]>
Signed-off-by David S. Miller <[email protected]>
Signed-off-by Greg Kroah-Hartman <[email protected]>
---
 include/net/ip.h          |    1 -
 net/ipv4/ip_forward.c     |    2 +-
 net/ipv4/ip_output.c      |    6 ++----
 net/ipv4/ip_tunnel_core.c |   11 -----------
 net/ipv4/ipmr.c           |    2 +-
 5 files changed, 4 insertions(+), 18 deletions(-)
include/net/ip.h +0 -1
@@ -47,7 +47,6 @@ struct inet_skb_parm {
 #define IPSKB_REROUTED		BIT(4)
 #define IPSKB_DOREDIRECT	BIT(5)
 #define IPSKB_FRAG_PMTU		BIT(6)
-#define IPSKB_FRAG_SEGS		BIT(7)
 
 	u16			frag_max_size;
 };
net/ipv4/ip_forward.c +1 -1
@@ -117,7 +117,7 @@ int ip_forward(struct sk_buff *skb)
 	if (opt->is_strictroute && rt->rt_uses_gateway)
 		goto sr_failed;
 
-	IPCB(skb)->flags |= IPSKB_FORWARDED | IPSKB_FRAG_SEGS;
+	IPCB(skb)->flags |= IPSKB_FORWARDED;
 	mtu = ip_dst_mtu_maybe_forward(&rt->dst, true);
 	if (ip_exceeds_mtu(skb, mtu)) {
 		IP_INC_STATS(net, IPSTATS_MIB_FRAGFAILS);
net/ipv4/ip_output.c +2 -4
@@ -223,11 +223,9 @@ static int ip_finish_output_gso(struct n
 	struct sk_buff *segs;
 	int ret = 0;
 
-	/* common case: fragmentation of segments is not allowed,
-	 * or seglen is <= mtu
+	/* common case: seglen is <= mtu
 	 */
-	if (((IPCB(skb)->flags & IPSKB_FRAG_SEGS) == 0) ||
-	      skb_gso_validate_mtu(skb, mtu))
+	if (skb_gso_validate_mtu(skb, mtu))
 		return ip_finish_output2(net, sk, skb);
 
 	/* Slowpath -  GSO segment length is exceeding the dst MTU.
net/ipv4/ip_tunnel_core.c +0 -11
@@ -63,7 +63,6 @@ void iptunnel_xmit(struct sock *sk, stru
 	int pkt_len = skb->len - skb_inner_network_offset(skb);
 	struct net *net = dev_net(rt->dst.dev);
 	struct net_device *dev = skb->dev;
-	int skb_iif = skb->skb_iif;
 	struct iphdr *iph;
 	int err;
 

@@ -73,16 +72,6 @@ void iptunnel_xmit(struct sock *sk, stru
 	skb_dst_set(skb, &rt->dst);
 	memset(IPCB(skb), 0, sizeof(*IPCB(skb)));
 
-	if (skb_iif && !(df & htons(IP_DF))) {
-		/* Arrived from an ingress interface, got encapsulated, with
-		 * fragmentation of encapulating frames allowed.
-		 * If skb is gso, the resulting encapsulated network segments
-		 * may exceed dst mtu.
-		 * Allow IP Fragmentation of segments.
-		 */
-		IPCB(skb)->flags |= IPSKB_FRAG_SEGS;
-	}
-
 	/* Push down and install the IP header. */
 	skb_push(skb, sizeof(struct iphdr));
 	skb_reset_network_header(skb);
net/ipv4/ipmr.c +1 -1
@@ -1749,7 +1749,7 @@ static void ipmr_queue_xmit(struct net *
 		vif->dev->stats.tx_bytes += skb->len;
 	}
 
-	IPCB(skb)->flags |= IPSKB_FORWARDED | IPSKB_FRAG_SEGS;
+	IPCB(skb)->flags |= IPSKB_FORWARDED;
 
 	/* RFC1584 teaches, that DVMRP/PIM router must deliver packets locally
 	 * not only before forwarding, but after forwarding on all output

Patches currently in stable-queue which might be from [email protected] are

queue-4.8/ipv4-allow-local-fragmentation-in-ip_finish_output_gso.patch