[iptables PATCH 3/4] xshared: Prefer xtables_chain_protos lookup over getprotoent

[Phil Sutter <phil@nwl.cc>]

When dumping a large ruleset, common protocol matches such as for TCP
port number significantly slow down rule printing due to repeated calls
for getprotobynumber(). The latter does not involve any caching, so
/etc/protocols is consulted over and over again.

As a simple countermeasure, make functions converting between proto
number and name prefer the built-in list of "well-known" protocols. This
is not a perfect solution, repeated rules for protocol names libxtables
does not cache (e.g. igmp or dccp) will still be slow. Implementing
getprotoent() result caching could solve this.

As a side-effect, explicit check for pseudo-protocol "all" may be
dropped as it is contained in the built-in list and therefore immutable.

Also update xtables_chain_protos entries a bit to align with typical
/etc/protocols contents. The testsuite assumes those names, so the
preferred ones prior to this patch are indeed uncommon nowadays.

Signed-off-by: Phil Sutter <phil@nwl.cc>
---
 iptables/xshared.c   |  8 ++++----
 libxtables/xtables.c | 19 ++++++-------------
 2 files changed, 10 insertions(+), 17 deletions(-)

diff --git a/iptables/xshared.c b/iptables/xshared.c
index 50a1d48a55ebe..43321d3b5358c 100644
--- a/iptables/xshared.c
+++ b/iptables/xshared.c
@@ -53,16 +53,16 @@ proto_to_name(uint16_t proto, int nolookup)
 {
 	unsigned int i;
 
+	for (i = 0; xtables_chain_protos[i].name != NULL; ++i)
+		if (xtables_chain_protos[i].num == proto)
+			return xtables_chain_protos[i].name;
+
 	if (proto && !nolookup) {
 		struct protoent *pent = getprotobynumber(proto);
 		if (pent)
 			return pent->p_name;
 	}
 
-	for (i = 0; xtables_chain_protos[i].name != NULL; ++i)
-		if (xtables_chain_protos[i].num == proto)
-			return xtables_chain_protos[i].name;
-
 	return NULL;
 }
 
diff --git a/libxtables/xtables.c b/libxtables/xtables.c
index 87424d045466b..094cbd87ec1ed 100644
--- a/libxtables/xtables.c
+++ b/libxtables/xtables.c
@@ -2101,10 +2101,11 @@ const struct xtables_pprot xtables_chain_protos[] = {
 	{"udp",       IPPROTO_UDP},
 	{"udplite",   IPPROTO_UDPLITE},
 	{"icmp",      IPPROTO_ICMP},
-	{"icmpv6",    IPPROTO_ICMPV6},
 	{"ipv6-icmp", IPPROTO_ICMPV6},
+	{"icmpv6",    IPPROTO_ICMPV6},
 	{"esp",       IPPROTO_ESP},
 	{"ah",        IPPROTO_AH},
+	{"mobility-header", IPPROTO_MH},
 	{"ipv6-mh",   IPPROTO_MH},
 	{"mh",        IPPROTO_MH},
 	{"all",       0},
@@ -2120,23 +2121,15 @@ xtables_parse_protocol(const char *s)
 	if (xtables_strtoui(s, NULL, &proto, 0, UINT8_MAX))
 		return proto;
 
-	/* first deal with the special case of 'all' to prevent
-	 * people from being able to redefine 'all' in nsswitch
-	 * and/or provoke expensive [not working] ldap/nis/...
-	 * lookups */
-	if (strcmp(s, "all") == 0)
-		return 0;
+	for (i = 0; xtables_chain_protos[i].name != NULL; ++i) {
+		if (strcmp(s, xtables_chain_protos[i].name) == 0)
+			return xtables_chain_protos[i].num;
+	}
 
 	pent = getprotobyname(s);
 	if (pent != NULL)
 		return pent->p_proto;
 
-	for (i = 0; i < ARRAY_SIZE(xtables_chain_protos); ++i) {
-		if (xtables_chain_protos[i].name == NULL)
-			continue;
-		if (strcmp(s, xtables_chain_protos[i].name) == 0)
-			return xtables_chain_protos[i].num;
-	}
 	xt_params->exit_err(PARAMETER_PROBLEM,
 		"unknown protocol \"%s\" specified", s);
 	return -1;
-- 
2.34.1