[PATCH -next] netfilter: nfnetlink: work around wrong endianess with old nft userspace

[Florian Westphal <fw@strlen.de>]

The nfgenmsg res_id is __be16.  Unfortunately nftables batch support uses
host byte order.

This adds a compat workaround for old nft userspace.

Suggested-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Florian Westphal <fw@strlen.de>
---
 net/netfilter/nfnetlink.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/net/netfilter/nfnetlink.c b/net/netfilter/nfnetlink.c
index 0c0e8ec..2e255ad 100644
--- a/net/netfilter/nfnetlink.c
+++ b/net/netfilter/nfnetlink.c
@@ -276,18 +276,24 @@ enum {
 };
 
 static void nfnetlink_rcv_batch(struct sk_buff *skb, struct nlmsghdr *nlh,
-				u_int16_t subsys_id)
+				__be16 __subsys_id)
 {
 	struct sk_buff *oskb = skb;
 	struct net *net = sock_net(skb->sk);
 	const struct nfnetlink_subsystem *ss;
 	const struct nfnl_callback *nc;
 	static LIST_HEAD(err_list);
+	u16 subsys_id = ntohs(__subsys_id);
 	u32 status;
 	int err;
 
-	if (subsys_id >= NFNL_SUBSYS_COUNT)
-		return netlink_ack(skb, nlh, -EINVAL);
+	if (subsys_id >= NFNL_SUBSYS_COUNT) {
+		/* Work around old nft using host byte order */
+		if (NFNL_SUBSYS_NFTABLES != (__force __u16) __subsys_id)
+			return netlink_ack(skb, nlh, -EINVAL);
+
+		subsys_id = (__force __u16) __subsys_id;
+	}
 replay:
 	status = 0;
 
-- 
2.0.5