Patch "udplite: fix partial checksum initialization" 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

udplite: fix partial checksum initialization

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:
udplite-fix-partial-checksum-initialization.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: Alexey Kodanev <[email protected]>
Date: Thu, 15 Feb 2018 20:18:43 +0300
Subject: udplite: fix partial checksum initialization

From: Alexey Kodanev <[email protected]>

[ Upstream commit 15f35d49c93f4fa9875235e7bf3e3783d2dd7a1b ]

Since UDP-Lite is always using checksum, the following path is triggered when calculating pseudo header for it:

udp4_csum_init() or udp6_csum_init()
skb_checksum_init_zero_check()
__skb_checksum_validate_complete()

The problem can appear if skb->len is less than CHECKSUM_BREAK. In this particular case __skb_checksum_validate_complete() also invokes __skb_checksum_complete(skb). If UDP-Lite is using partial checksum that covers only part of a packet, the function will return bad checksum and the packet will be dropped.

It can be fixed if we skip skb_checksum_init_zero_check() and only set the required pseudo header checksum for UDP-Lite with partial checksum before udp4_csum_init()/udp6_csum_init() functions return.

---
 include/net/udplite.h   |    1 +
 net/ipv4/udp.c          |    5 +++++
 net/ipv6/ip6_checksum.c |    5 +++++
 3 files changed, 11 insertions(+)

@@ -62,6 +62,7 @@ static inline int udplite_checksum_init(
 		UDP_SKB_CB(skb)->cscov = cscov;
 		if (skb->ip_summed == CHECKSUM_COMPLETE)
 			skb->ip_summed = CHECKSUM_NONE;
+		skb->csum_valid = 0;
         }
 
 	return 0;

@@ -1713,6 +1713,11 @@ static inline int udp4_csum_init(struct
 		err = udplite_checksum_init(skb, uh);
 		if (err)
 			return err;
+
+		if (UDP_SKB_CB(skb)->partial_cov) {
+			skb->csum = inet_compute_pseudo(skb, proto);
+			return 0;
+		}
 	}
 
 	/* Note, we are only interested in != 0 or == 0, thus the

@@ -72,6 +72,11 @@ int udp6_csum_init(struct sk_buff *skb,
 		err = udplite_checksum_init(skb, uh);
 		if (err)
 			return err;
+
+		if (UDP_SKB_CB(skb)->partial_cov) {
+			skb->csum = ip6_compute_pseudo(skb, proto);
+			return 0;
+		}
 	}
 
 	/* To support RFC 6936 (allow zero checksum in UDP/IPV6 for tunnels)

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

queue-4.9/sctp-fix-dst-refcnt-leak-in-sctp_v6_get_dst.patch queue-4.9/udplite-fix-partial-checksum-initialization.patch queue-4.9/sctp-verify-size-of-a-new-chunk-in-_sctp_make_chunk.patch