ipv6: Add flow label to route get requests

The default IPv6 multipath hash policy takes the flow label into account
when calculating a multipath hash and previous patches added a flow
label selector to IPv6 FIB rules.

Allow user space to specify a flow label in route get requests by adding
a new netlink attribute and using its value to populate the "flowlabel"
field in the IPv6 flow info structure prior to a route lookup.

Deny the attribute in RTM_{NEW,DEL}ROUTE requests by checking for it in
rtm_to_fib6_config() and returning an error if present.

A subsequent patch will use this capability to test the new flow label
selector in IPv6 FIB rules.

Reviewed-by: Petr Machata <[e-mail]>
Signed-off-by: Ido Schimmel <[e-mail]>
Reviewed-by: Guillaume Nault <[e-mail]>
Signed-off-by: Paolo Abeni <[e-mail]>

include/uapi/linux/rtnetlink.h

···
 	RTA_SPORT,
 	RTA_DPORT,
 	RTA_NH_ID,
+	RTA_FLOWLABEL,
 	__RTA_MAX
 };
 

net/ipv6/route.c

···
 	[RTA_SPORT]		= { .type = NLA_U16 },
 	[RTA_DPORT]		= { .type = NLA_U16 },
 	[RTA_NH_ID]		= { .type = NLA_U32 },
+	[RTA_FLOWLABEL]		= { .type = NLA_BE32 },
 };
 
 static int rtm_to_fib6_config(struct sk_buff *skb, struct nlmsghdr *nlh,
···
 	if (rtm->rtm_tos) {
 		NL_SET_ERR_MSG(extack,
 			       "Invalid dsfield (tos): option not available for IPv6");
+		goto errout;
+	}
+
+	if (tb[RTA_FLOWLABEL]) {
+		NL_SET_ERR_MSG_ATTR(extack, tb[RTA_FLOWLABEL],
+				    "Flow label cannot be specified for this operation");
 		goto errout;
 	}
 
···
 		return -EINVAL;
 	}
 
+	if (tb[RTA_FLOWLABEL] &&
+	    (nla_get_be32(tb[RTA_FLOWLABEL]) & ~IPV6_FLOWLABEL_MASK)) {
+		NL_SET_ERR_MSG_ATTR(extack, tb[RTA_FLOWLABEL],
+				    "Invalid flow label");
+		return -EINVAL;
+	}
+
 	for (i = 0; i <= RTA_MAX; i++) {
 		if (!tb[i])
 			continue;
···
 		case RTA_SPORT:
 		case RTA_DPORT:
 		case RTA_IP_PROTO:
+		case RTA_FLOWLABEL:
 			break;
 		default:
 			NL_SET_ERR_MSG_MOD(extack, "Unsupported attribute in get route request");
···
 	struct sk_buff *skb;
 	struct rtmsg *rtm;
 	struct flowi6 fl6 = {};
+	__be32 flowlabel;
 	bool fibmatch;
 
 	err = inet6_rtm_valid_getroute_req(in_skb, nlh, tb, extack);
···
 
 	err = -EINVAL;
 	rtm = nlmsg_data(nlh);
-	fl6.flowlabel = ip6_make_flowinfo(rtm->rtm_tos, 0);
 	fibmatch = !!(rtm->rtm_flags & RTM_F_FIB_MATCH);
 
 	if (tb[RTA_SRC]) {
···
 		if (err)
 			goto errout;
 	}
+
+	flowlabel = nla_get_be32_default(tb[RTA_FLOWLABEL], 0);
+	fl6.flowlabel = ip6_make_flowinfo(rtm->rtm_tos, flowlabel);
 
 	if (iif) {
 		struct net_device *dev;