ipv4: fib: Fix metrics match when deleting a route

The recently added fib_metrics_match() causes a regression for routes
with both RTAX_FEATURES and RTAX_CC_ALGO if the latter has
TCP_CONG_NEEDS_ECN flag set:

| # ip link add d0 type dummy
| # ip link set d0 up
| # ip route add 172.29.29.0/24 dev d0 features ecn congctl dctcp
| # ip route del 172.29.29.0/24 dev d0 features ecn congctl dctcp
| RTNETLINK answers: No such process

During route insertion, fib_convert_metrics() detects that the given CC
algo requires ECN and hence sets DST_FEATURE_ECN_CA bit in
RTAX_FEATURES.

During route deletion though, fib_metrics_match() compares stored
RTAX_FEATURES value with that from userspace (which obviously has no
knowledge about DST_FEATURE_ECN_CA) and fails.

Fixes: 5f9ae3d9 ("ipv4: do metrics match when looking up and deleting a route")
Signed-off-by: NPhil Sutter <phil@nwl.cc>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/fib_semantics.c

@@ -698,7 +698,7 @@ bool fib_metrics_match(struct fib_config *cfg, struct fib_info *fi)
 
 	nla_for_each_attr(nla, cfg->fc_mx, cfg->fc_mx_len, remaining) {
 		int type = nla_type(nla);
-		u32 val;
+		u32 fi_val, val;
 
 		if (!type)
 			continue;
@@ -715,7 +715,11 @@ bool fib_metrics_match(struct fib_config *cfg, struct fib_info *fi)
 			val = nla_get_u32(nla);
 		}
 
-		if (fi->fib_metrics->metrics[type - 1] != val)
+		fi_val = fi->fib_metrics->metrics[type - 1];
+		if (type == RTAX_FEATURES)
+			fi_val &= ~DST_FEATURE_ECN_CA;
+
+		if (fi_val != val)
 			return false;
 	}