[PATCH 3.16 104/294] net: avoid skb_warn_bad_offload false positives on UFO

[Ben Hutchings]

3.16.50-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Willem de Bruijn <willemb@xxxxxxxxxx>

commit 8d63bee643f1fb53e472f0e135cae4eb99d62d19 upstream.

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/

Fixes: b2504a5dbef3 ("net: reduce skb_warn_bad_offload() noise")
Signed-off-by: Willem de Bruijn <willemb@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 net/core/dev.c         | 2 +-
 net/ipv4/udp_offload.c | 2 +-
 net/ipv6/udp_offload.c | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2414,7 +2414,7 @@ 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;
 }
--- a/net/ipv4/udp_offload.c
+++ b/net/ipv4/udp_offload.c
@@ -93,7 +93,7 @@ static struct sk_buff *udp4_ufo_fragment
 	csum = skb_checksum(skb, offset, skb->len - offset, 0);
 	offset += skb->csum_offset;
 	*(__sum16 *)(skb->data + offset) = csum_fold(csum);
-	skb->ip_summed = CHECKSUM_NONE;
+	skb->ip_summed = CHECKSUM_UNNECESSARY;
 
 	/* Fragment the skb. IP headers of the fragments are updated in
 	 * inet_gso_segment()
--- a/net/ipv6/udp_offload.c
+++ b/net/ipv6/udp_offload.c
@@ -90,7 +90,7 @@ static struct sk_buff *udp6_ufo_fragment
 		csum = skb_checksum(skb, offset, skb->len - offset, 0);
 		offset += skb->csum_offset;
 		*(__sum16 *)(skb->data + offset) = csum_fold(csum);
-		skb->ip_summed = CHECKSUM_NONE;
+		skb->ip_summed = CHECKSUM_UNNECESSARY;
 
 		/* Check if there is enough headroom to insert fragment header. */
 		tnl_hlen = skb_tnl_header_len(skb);