linux-kernel - [PATCH 3.16 019/157] sctp: get sctphdr by offset in sctp_compute

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Message-ID: <lsq.1565469607.137194373@decadent.org.uk>
Date:   Sat, 10 Aug 2019 21:40:07 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Li Shuang" <shuali@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        "Xin Long" <lucien.xin@...il.com>
Subject: [PATCH 3.16 019/157] sctp: get sctphdr by offset in
 sctp_compute_cksum

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

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

From: Xin Long <lucien.xin@...il.com>

commit 273160ffc6b993c7c91627f5a84799c66dfe4dee upstream.

sctp_hdr(skb) only works when skb->transport_header is set properly.

But in Netfilter, skb->transport_header for ipv6 is not guaranteed
to be right value for sctphdr. It would cause to fail to check the
checksum for sctp packets.

So fix it by using offset, which is always right in all places.

v1->v2:
  - Fix the changelog.

Fixes: e6d8b64b34aa ("net: sctp: fix and consolidate SCTP checksumming code")
Reported-by: Li Shuang <shuali@...hat.com>
Signed-off-by: Xin Long <lucien.xin@...il.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 include/net/sctp/checksum.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/include/net/sctp/checksum.h
+++ b/include/net/sctp/checksum.h
@@ -61,7 +61,7 @@ static inline __wsum sctp_csum_combine(_
 static inline __le32 sctp_compute_cksum(const struct sk_buff *skb,
 					unsigned int offset)
 {
-	struct sctphdr *sh = sctp_hdr(skb);
+	struct sctphdr *sh = (struct sctphdr *)(skb->data + offset);
 	const struct skb_checksum_ops ops = {
 		.update  = sctp_csum_update,
 		.combine = sctp_csum_combine,