netfilter: ctnetlink: honor CTA_MARK_MASK when setting ctmark

Useful to only set a particular range of the conntrack mark while
leaving exisiting parts of the value alone, e.g. when setting
conntrack marks via NFQUEUE.

Follows same scheme as MARK/CONNMARK targets, i.e. the mask defines
those bits that should be altered.  No mask is equal to '~0', ie.
the old value is replaced by new one.
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_conntrack_netlink.c

@@ -2118,8 +2118,16 @@ ctnetlink_nfqueue_parse_ct(const struct nlattr *cda[], struct nf_conn *ct)
 			return err;
 	}
 #if defined(CONFIG_NF_CONNTRACK_MARK)
-	if (cda[CTA_MARK])
-		ct->mark = ntohl(nla_get_be32(cda[CTA_MARK]));
+	if (cda[CTA_MARK]) {
+		u32 mask = 0, mark, newmark;
+		if (cda[CTA_MARK_MASK])
+			mask = ~ntohl(nla_get_be32(cda[CTA_MARK_MASK]));
+
+		mark = ntohl(nla_get_be32(cda[CTA_MARK]));
+		newmark = (ct->mark & mask) ^ mark;
+		if (newmark != ct->mark)
+			ct->mark = newmark;
+	}
 #endif
 	return 0;
 }