Patch "net: avoid skb_warn_bad_offload false positives on UFO" has been added to the 4.9-stable tree

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

net: avoid skb_warn_bad_offload false positives on UFO

to the 4.9-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:
net-avoid-skb_warn_bad_offload-false-positives-on-ufo.patch
and it can be found in the queue-4.9 subdirectory.

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

From: Willem de Bruijn <[email protected]>
Date: Tue, 8 Aug 2017 14:22:55 -0400
Subject: net: avoid skb_warn_bad_offload false positives on UFO

From: Willem de Bruijn <[email protected]>

[ Upstream commit 8d63bee643f1fb53e472f0e135cae4eb99d62d19 ]

skb_warn_bad_offload triggers a warning when an skb enters the GSO stack at __skb_gso_segment that does not have CHECKSUM_PARTIAL checksum offload set.

Commit b2504a5dbef3 ("net: reduce skb_warn_bad_offload() noise") observed that SKB_GSO_DODGY producers can trigger the check and that passing those packets through the GSO handlers will fix it up. But, the software UFO handler will set ip_summed to CHECKSUM_NONE.

When __skb_gso_segment is called from the receive path, this triggers the warning again.

Make UFO set CHECKSUM_UNNECESSARY instead of CHECKSUM_NONE. On Tx these two are equivalent. On Rx, this better matches the skb state (checksum computed), as CHECKSUM_NONE here means no checksum computed.

See also this thread for context:
http://patchwork.ozlabs.org/patch/799015/

---
 net/core/dev.c         |    2 +-
 net/ipv4/udp_offload.c |    2 +-
 net/ipv6/udp_offload.c |    2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

@@ -2703,7 +2703,7 @@ static inline bool skb_needs_check(struc
 {
 	if (tx_path)
 		return skb->ip_summed != CHECKSUM_PARTIAL &&
-		       skb->ip_summed != CHECKSUM_NONE;
+		       skb->ip_summed != CHECKSUM_UNNECESSARY;
 
 	return skb->ip_summed == CHECKSUM_NONE;
 }

@@ -232,7 +232,7 @@ static struct sk_buff *udp4_ufo_fragment
 	if (uh->check == 0)
 		uh->check = CSUM_MANGLED_0;
 
-	skb->ip_summed = CHECKSUM_NONE;
+	skb->ip_summed = CHECKSUM_UNNECESSARY;
 
 	/* If there is no outer header we can fake a checksum offload
 	 * due to the fact that we have already done the checksum in

@@ -72,7 +72,7 @@ static struct sk_buff *udp6_ufo_fragment
 		if (uh->check == 0)
 			uh->check = CSUM_MANGLED_0;
 
-		skb->ip_summed = CHECKSUM_NONE;
+		skb->ip_summed = CHECKSUM_UNNECESSARY;
 
 		/* If there is no outer header we can fake a checksum offload
 		 * due to the fact that we have already done the checksum in

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

queue-4.9/net-avoid-skb_warn_bad_offload-false-positives-on-ufo.patch queue-4.9/packet-fix-tp_reserve-race-in-packet_set_ring.patch queue-4.9/udp-consistently-apply-ufo-or-fragmentation.patch