Patch "net: mangle zero checksum in skb_checksum_help()" 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

net: mangle zero checksum in skb_checksum_help()

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:
net-mangle-zero-checksum-in-skb_checksum_help.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: Eric Dumazet <[email protected]>
Date: Sat, 29 Oct 2016 11:02:36 -0700
Subject: net: mangle zero checksum in skb_checksum_help()

From: Eric Dumazet <[email protected]>

[ Upstream commit 4f2e4ad56a65f3b7d64c258e373cb71e8d2499f4 ]

Sending zero checksum is ok for TCP, but not for UDP.

UDPv6 receiver should by default drop a frame with a 0 checksum, and UDPv4 would not verify the checksum and might accept a corrupted packet.

Simply replace such checksum by 0xffff, regardless of transport.

This error was caught on SIT tunnels, but seems generic.

---
 net/core/dev.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -2462,7 +2462,7 @@ int skb_checksum_help(struct sk_buff *sk
 			goto out;
 	}
 
-	*(__sum16 *)(skb->data + offset) = csum_fold(csum);
+	*(__sum16 *)(skb->data + offset) = csum_fold(csum) ?: CSUM_MANGLED_0;
 out_set_summed:
 	skb->ip_summed = CHECKSUM_NONE;
 out:

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

queue-4.4/net-__skb_flow_dissect-must-cap-its-return-value.patch queue-4.4/tcp-take-care-of-truncations-done-by-sk_filter.patch queue-4.4/net-clear-sk_err_soft-in-sk_clone_lock.patch queue-4.4/net-mangle-zero-checksum-in-skb_checksum_help.patch queue-4.4/ipv6-dccp-fix-out-of-bound-access-in-dccp_v6_err.patch queue-4.4/ipv6-dccp-add-missing-bind_conflict-to-dccp_ipv6_mapped.patch queue-4.4/tcp-fix-potential-memory-corruption.patch queue-4.4/dccp-do-not-send-reset-to-already-closed-sockets.patch queue-4.4/dccp-fix-out-of-bound-access-in-dccp_v4_err.patch queue-4.4/sock-fix-sendmmsg-for-partial-sendmsg.patch