Patch "sched: act_csum: don't mangle TCP and UDP GSO packets" has been added to the 4.4-stable tree

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

sched: act_csum: don't mangle TCP and UDP GSO packets

to the 4.4-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:
sched-act_csum-don-t-mangle-tcp-and-udp-gso-packets.patch
and it can be found in the queue-4.4 subdirectory.

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

From: Davide Caratti <[email protected]>
Date: Thu, 23 Mar 2017 10:39:40 +0100
Subject: sched: act_csum: don't mangle TCP and UDP GSO packets

From: Davide Caratti <[email protected]>

[ Upstream commit add641e7dee31b36aee83412c29e39dd1f5e0c9c ]

after act_csum computes the checksum on skbs carrying GSO TCP/UDP packets, subsequent segmentation fails because skb_needs_check(skb, true) returns true. Because of that, skb_warn_bad_offload() is invoked and the following message is displayed:

WARNING: CPU: 3 PID: 28 at net/core/dev.c:2553 skb_warn_bad_offload+0xf0/0xfd

<...>

  [<ffffffff8171f486>] skb_warn_bad_offload+0xf0/0xfd
  [<ffffffff8161304c>] __skb_gso_segment+0xec/0x110
  [<ffffffff8161340d>] validate_xmit_skb+0x12d/0x2b0
  [<ffffffff816135d2>] validate_xmit_skb_list+0x42/0x70
  [<ffffffff8163c560>] sch_direct_xmit+0xd0/0x1b0
  [<ffffffff8163c760>] __qdisc_run+0x120/0x270
  [<ffffffff81613b3d>] __dev_queue_xmit+0x23d/0x690
  [<ffffffff81613fa0>] dev_queue_xmit+0x10/0x20

Since GSO is able to compute checksum on individual segments of such skbs, we can simply skip mangling the packet.

---
 net/sched/act_csum.c |   12 ++++++++++++
 1 file changed, 12 insertions(+)

@@ -175,6 +175,9 @@ static int tcf_csum_ipv4_tcp(struct sk_b
 	struct tcphdr *tcph;
 	const struct iphdr *iph;
 
+	if (skb_is_gso(skb) && skb_shinfo(skb)->gso_type & SKB_GSO_TCPV4)
+		return 1;
+
 	tcph = tcf_csum_skb_nextlayer(skb, ihl, ipl, sizeof(*tcph));
 	if (tcph == NULL)
 		return 0;

@@ -196,6 +199,9 @@ static int tcf_csum_ipv6_tcp(struct sk_b
 	struct tcphdr *tcph;
 	const struct ipv6hdr *ip6h;
 
+	if (skb_is_gso(skb) && skb_shinfo(skb)->gso_type & SKB_GSO_TCPV6)
+		return 1;
+
 	tcph = tcf_csum_skb_nextlayer(skb, ihl, ipl, sizeof(*tcph));
 	if (tcph == NULL)
 		return 0;

@@ -219,6 +225,9 @@ static int tcf_csum_ipv4_udp(struct sk_b
 	const struct iphdr *iph;
 	u16 ul;
 
+	if (skb_is_gso(skb) && skb_shinfo(skb)->gso_type & SKB_GSO_UDP)
+		return 1;
+
 	/*
 	 * Support both UDP and UDPLITE checksum algorithms, Don't use
 	 * udph->len to get the real length without any protocol check,

@@ -272,6 +281,9 @@ static int tcf_csum_ipv6_udp(struct sk_b
 	const struct ipv6hdr *ip6h;
 	u16 ul;
 
+	if (skb_is_gso(skb) && skb_shinfo(skb)->gso_type & SKB_GSO_UDP)
+		return 1;
+
 	/*
 	 * Support both UDP and UDPLITE checksum algorithms, Don't use
 	 * udph->len to get the real length without any protocol check,

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

queue-4.4/sched-act_csum-don-t-mangle-tcp-and-udp-gso-packets.patch