nftutils: add and use wrappers for getprotoby{name,number}_r(), getservbyport_r()

We should aim to use the thread-safe variants of getprotoby{name,number}
and getservbyport(). However, they may not be available with other libc,
so it requires a configure check. As that is cumbersome, add wrappers
that do that at one place.

These wrappers are thread-safe, if libc provides the reentrant versions.
Use them.

Signed-off-by: Thomas Haller <thaller@redhat.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

7 files changed, 161 insertions, 30 deletions

diff --git a/configure.ac b/configure.ac
index b0201ac3..42f0dc4c 100644
--- a/configure.ac
+++ b/configure.ac
@@ -108,6 +108,10 @@ AC_DEFINE([HAVE_LIBJANSSON], [1], [Define if you have libjansson])
 ])
 AM_CONDITIONAL([BUILD_JSON], [test "x$with_json" != xno])
 
+AC_CHECK_DECLS([getprotobyname_r, getprotobynumber_r, getservbyport_r], [], [], [[
+#include <netdb.h>
+]])
+
 AC_CONFIG_FILES([					\
 		Makefile				\
 		libnftables.pc				\
diff --git a/src/Makefile.am b/src/Makefile.am
index ace38bd7..ad22a918 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -64,6 +64,8 @@ libnftables_la_SOURCES =			\
 		segtree.c			\
 		gmputil.c			\
 		utils.c				\
+		nftutils.c			\
+		nftutils.h			\
 		erec.c				\
 		mnl.c				\
 		iface.c				\
diff --git a/src/datatype.c b/src/datatype.c
index da802a18..381320ea 100644
--- a/src/datatype.c
+++ b/src/datatype.c
@@ -29,6 +29,7 @@
 #include <netlink.h>
 #include <json.h>
 #include <misspell.h>
+#include "nftutils.h"
 
 #include <netinet/ip_icmp.h>
 
@@ -697,12 +698,11 @@ const struct datatype ip6addr_type = {
 static void inet_protocol_type_print(const struct expr *expr,
 				      struct output_ctx *octx)
 {
-	struct protoent *p;
-
 	if (!nft_output_numeric_proto(octx)) {
-		p = getprotobynumber(mpz_get_uint8(expr->value));
-		if (p != NULL) {
-			nft_print(octx, "%s", p->p_name);
+		char name[NFT_PROTONAME_MAXSIZE];
+
+		if (nft_getprotobynumber(mpz_get_uint8(expr->value), name, sizeof(name))) {
+			nft_print(octx, "%s", name);
 			return;
 		}
 	}
@@ -711,15 +711,15 @@ static void inet_protocol_type_print(const struct expr *expr,
 
 static void inet_protocol_type_describe(struct output_ctx *octx)
 {
-	struct protoent *p;
 	uint8_t protonum;
 
 	for (protonum = 0; protonum < UINT8_MAX; protonum++) {
-		p = getprotobynumber(protonum);
-		if (!p)
+		char name[NFT_PROTONAME_MAXSIZE];
+
+		if (!nft_getprotobynumber(protonum, name, sizeof(name)))
 			continue;
 
-		nft_print(octx, "\t%-30s\t%u\n", p->p_name, protonum);
+		nft_print(octx, "\t%-30s\t%u\n", name, protonum);
 	}
 }
 
@@ -727,7 +727,6 @@ static struct error_record *inet_protocol_type_parse(struct parse_ctx *ctx,
 						     const struct expr *sym,
 						     struct expr **res)
 {
-	struct protoent *p;
 	uint8_t proto;
 	uintmax_t i;
 	char *end;
@@ -740,11 +739,13 @@ static struct error_record *inet_protocol_type_parse(struct parse_ctx *ctx,
 
 		proto = i;
 	} else {
-		p = getprotobyname(sym->identifier);
-		if (p == NULL)
+		int r;
+
+		r = nft_getprotobyname(sym->identifier);
+		if (r < 0)
 			return error(&sym->location, "Could not resolve protocol name");
 
-		proto = p->p_proto;
+		proto = r;
 	}
 
 	*res = constant_expr_alloc(&sym->location, &inet_protocol_type,
@@ -768,12 +769,12 @@ const struct datatype inet_protocol_type = {
 static void inet_service_print(const struct expr *expr, struct output_ctx *octx)
 {
 	uint16_t port = mpz_get_be16(expr->value);
-	const struct servent *s = getservbyport(port, NULL);
+	char name[NFT_SERVNAME_MAXSIZE];
 
-	if (s == NULL)
+	if (!nft_getservbyport(port, NULL, name, sizeof(name)))
 		nft_print(octx, "%hu", ntohs(port));
 	else
-		nft_print(octx, "\"%s\"", s->s_name);
+		nft_print(octx, "\"%s\"", name);
 }
 
 void inet_service_type_print(const struct expr *expr, struct output_ctx *octx)
diff --git a/src/json.c b/src/json.c
index 366c0edf..31dd1856 100644
--- a/src/json.c
+++ b/src/json.c
@@ -15,6 +15,7 @@
 #include <netlink.h>
 #include <rule.h>
 #include <rt.h>
+#include "nftutils.h"
 
 #include <netdb.h>
 #include <netinet/icmp6.h>
@@ -298,10 +299,10 @@ static json_t *chain_print_json(const struct chain *chain)
 
 static json_t *proto_name_json(uint8_t proto)
 {
-	const struct protoent *p = getprotobynumber(proto);
+	char name[NFT_PROTONAME_MAXSIZE];
 
-	if (p)
-		return json_string(p->p_name);
+	if (nft_getprotobynumber(proto, name, sizeof(name)))
+		return json_string(name);
 	return json_integer(proto);
 }
 
@@ -1094,12 +1095,11 @@ json_t *boolean_type_json(const struct expr *expr, struct output_ctx *octx)
 json_t *inet_protocol_type_json(const struct expr *expr,
 				struct output_ctx *octx)
 {
-	struct protoent *p;
-
 	if (!nft_output_numeric_proto(octx)) {
-		p = getprotobynumber(mpz_get_uint8(expr->value));
-		if (p != NULL)
-			return json_string(p->p_name);
+		char name[NFT_PROTONAME_MAXSIZE];
+
+		if (nft_getprotobynumber(mpz_get_uint8(expr->value), name, sizeof(name)))
+			return json_string(name);
 	}
 	return integer_type_json(expr, octx);
 }
@@ -1107,13 +1107,13 @@ json_t *inet_protocol_type_json(const struct expr *expr,
 json_t *inet_service_type_json(const struct expr *expr, struct output_ctx *octx)
 {
 	uint16_t port = mpz_get_be16(expr->value);
-	const struct servent *s = NULL;
+	char name[NFT_SERVNAME_MAXSIZE];
 
 	if (!nft_output_service(octx) ||
-	    (s = getservbyport(port, NULL)) == NULL)
+	    !nft_getservbyport(port, NULL, name, sizeof(name)))
 		return json_integer(ntohs(port));
 
-	return json_string(s->s_name);
+	return json_string(name);
 }
 
 json_t *mark_type_json(const struct expr *expr, struct output_ctx *octx)
diff --git a/src/nftutils.c b/src/nftutils.c
new file mode 100644
index 00000000..13f879dd
--- /dev/null
+++ b/src/nftutils.c
@@ -0,0 +1,102 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#include <config.h>
+
+#include "nftutils.h"
+
+#include <netdb.h>
+#include <string.h>
+#include <stdint.h>
+
+/* Buffer size used for getprotobynumber_r() and similar. The manual comments
+ * that a buffer of 1024 should be sufficient "for most applications"(??), so
+ * let's double it.  It still fits reasonably on the stack, so no need to
+ * choose a smaller one. */
+#define NETDB_BUFSIZE 2048
+
+bool nft_getprotobynumber(int proto, char *out_name, size_t name_len)
+{
+	const struct protoent *result;
+
+#if HAVE_DECL_GETPROTOBYNUMBER_R
+	struct protoent result_buf;
+	char buf[NETDB_BUFSIZE];
+	int r;
+
+	r = getprotobynumber_r(proto,
+	                       &result_buf,
+	                       buf,
+	                       sizeof(buf),
+	                       (struct protoent **) &result);
+	if (r != 0 || result != &result_buf)
+		result = NULL;
+#else
+	result = getprotobynumber(proto);
+#endif
+
+	if (!result)
+		return false;
+
+	if (strlen(result->p_name) >= name_len)
+		return false;
+	strcpy(out_name, result->p_name);
+	return true;
+}
+
+int nft_getprotobyname(const char *name)
+{
+	const struct protoent *result;
+
+#if HAVE_DECL_GETPROTOBYNAME_R
+	struct protoent result_buf;
+	char buf[NETDB_BUFSIZE];
+	int r;
+
+	r = getprotobyname_r(name,
+	                     &result_buf,
+	                     buf,
+	                     sizeof(buf),
+	                     (struct protoent **) &result);
+	if (r != 0 || result != &result_buf)
+		result = NULL;
+#else
+	result = getprotobyname(name);
+#endif
+
+	if (!result)
+		return -1;
+
+	if (result->p_proto < 0 || result->p_proto > UINT8_MAX)
+		return -1;
+	return (uint8_t) result->p_proto;
+}
+
+bool nft_getservbyport(int port, const char *proto, char *out_name, size_t name_len)
+{
+	const struct servent *result;
+
+#if HAVE_DECL_GETSERVBYPORT_R
+	struct servent result_buf;
+	char buf[NETDB_BUFSIZE];
+	int r;
+
+	r = getservbyport_r(port,
+	                    proto,
+	                    &result_buf,
+	                    buf,
+	                    sizeof(buf),
+	                    (struct servent**) &result);
+	if (r != 0 || result != &result_buf)
+		result = NULL;
+#else
+	result = getservbyport(port, proto);
+#endif
+
+	if (!result)
+		return false;
+
+	if (strlen(result->s_name) >= name_len)
+		return false;
+	strcpy(out_name, result->s_name);
+	return true;
+}
diff --git a/src/nftutils.h b/src/nftutils.h
new file mode 100644
index 00000000..cb584b9c
--- /dev/null
+++ b/src/nftutils.h
@@ -0,0 +1,21 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef NFTUTILS_H
+#define NFTUTILS_H
+
+#include <stdbool.h>
+#include <stddef.h>
+
+/* The maximum buffer size for (struct protoent).p_name. It is excessively large,
+ * while still reasonably fitting on the stack. Arbitrarily chosen. */
+#define NFT_PROTONAME_MAXSIZE 1024
+
+bool nft_getprotobynumber(int number, char *out_name, size_t name_len);
+int nft_getprotobyname(const char *name);
+
+/* The maximum buffer size for (struct servent).s_name. It is excessively large,
+ * while still reasonably fitting on the stack. Arbitrarily chosen. */
+#define NFT_SERVNAME_MAXSIZE 1024
+
+bool nft_getservbyport(int port, const char *proto, char *out_name, size_t name_len);
+
+#endif /* NFTUTILS_H */
diff --git a/src/rule.c b/src/rule.c
index 99c4f0bb..b59fcd3a 100644
--- a/src/rule.c
+++ b/src/rule.c
@@ -27,6 +27,7 @@
 #include <cache.h>
 #include <owner.h>
 #include <intervals.h>
+#include "nftutils.h"
 
 #include <libnftnl/common.h>
 #include <libnftnl/ruleset.h>
@@ -1666,10 +1667,10 @@ struct obj *obj_lookup_fuzzy(const char *obj_name,
 
 static void print_proto_name_proto(uint8_t l4, struct output_ctx *octx)
 {
-	const struct protoent *p = getprotobynumber(l4);
+	char name[NFT_PROTONAME_MAXSIZE];
 
-	if (p)
-		nft_print(octx, "%s", p->p_name);
+	if (nft_getprotobynumber(l4, name, sizeof(name)))
+		nft_print(octx, "%s", name);
 	else
 		nft_print(octx, "%d", l4);
 }