[PATCH net] net: fib_rules: add protocol check in rule_find

[Roopa Prabhu <roopa@cumulusnetworks.com>]

From: Roopa Prabhu <roopa@cumulusnetworks.com>

After commit f9d4b0c1e969 ("fib_rules: move common handling of newrule
delrule msgs into fib_nl2rule"), rule_find is strict about checking
for an existing rule. rule_find must check against all
user given attributes, else it may match against a subset
of attributes and return an existing rule.

In the below case, without support for protocol match, rule_find
will match only against 'table main' and return an existing rule.

$ip -4 rule add table main protocol boot
RTNETLINK answers: File exists

This patch adds protocol support to rule_find, forcing it to
check protocol match if given by the user.

Fixes: f9d4b0c1e969 ("fib_rules: move common handling of newrule delrule msgs into fib_nl2rule")
Signed-off-by: Roopa Prabhu <roopa@cumulusnetworks.com>
---
I spent some time looking at all match keys today and protocol
was the only missing one (protocol is not in a released kernel yet).
The only way this could be avoided is to move back to the old loose
rule_find. I am worried about this new strict checking surprising users,
but going back to the previous loose checking does not seem right either.
If there is a reason to believe that users did rely on the previous
behaviour, I will be happy to revert. Here is another example of old and
new behaviour.

old rule_find behaviour:
$ip -4 rule add table main protocol boot
$ip -4 rule add table main protocol boot
$ip -4 rule add table main protocol boot
$ip rule show
0:      from all lookup local 
32763:  from all lookup main  proto boot 
32764:  from all lookup main  proto boot 
32765:  from all lookup main  proto boot 
32766:  from all lookup main 
32767:  from all lookup default 

new rule_find behaviour (after this patch):
$ip -4 rule add table main protocol boot
$ip -4 rule add table main protocol boot
RTNETLINK answers: File exists

 net/core/fib_rules.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/core/fib_rules.c b/net/core/fib_rules.c
index bc8425d..5905567 100644
--- a/net/core/fib_rules.c
+++ b/net/core/fib_rules.c
@@ -444,6 +444,9 @@ static struct fib_rule *rule_find(struct fib_rules_ops *ops,
 		if (rule->ip_proto && r->ip_proto != rule->ip_proto)
 			continue;
 
+		if (rule->proto && r->proto != rule->proto)
+			continue;
+
 		if (fib_rule_port_range_set(&rule->sport_range) &&
 		    !fib_rule_port_range_compare(&r->sport_range,
 						 &rule->sport_range))
-- 
2.1.4