net: core: add missing check for uid_range in rule_exists.

Without this check, it is not possible to create two rules that
are identical except for their UID ranges. For example:

root@net-test:/# ip rule add prio 1000 lookup 300
root@net-test:/# ip rule add prio 1000 uidrange 100-200 lookup 300
RTNETLINK answers: File exists
root@net-test:/# ip rule add prio 1000 uidrange 100-199 lookup 100
root@net-test:/# ip rule add prio 1000 uidrange 200-299 lookup 200
root@net-test:/# ip rule add prio 1000 uidrange 300-399 lookup 100
RTNETLINK answers: File exists

Tested: https://android-review.googlesource.com/#/c/299980/Signed-off-by: NLorenzo Colitti <lorenzo@google.com>
Acked-by: NMaciej Żenczykowski <maze@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/fib_rules.c

@@ -343,6 +343,10 @@ static int rule_exists(struct fib_rules_ops *ops, struct fib_rule_hdr *frh,
 		if (r->l3mdev != rule->l3mdev)
 			continue;
 
+		if (!uid_eq(r->uid_range.start, rule->uid_range.start) ||
+		    !uid_eq(r->uid_range.end, rule->uid_range.end))
+			continue;
+
 		if (!ops->compare(r, frh, tb))
 			continue;
 		return 1;