src: add datatype->describe()

As an alternative to print the datatype values when no symbol table is
available. Use it to print protocols available via getprotobynumber()
which actually refers to /etc/protocols.

Not very efficient, getprotobynumber() causes a series of open()/close()
calls on /etc/protocols, but this is called from a non-critical path.

Closes: https://bugzilla.netfilter.org/show_bug.cgi?id=1503
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

2 files changed, 17 insertions, 0 deletions

diff --git a/src/datatype.c b/src/datatype.c
index 7382307e..fae1aa26 100644
--- a/src/datatype.c
+++ b/src/datatype.c
@@ -619,6 +619,20 @@ static void inet_protocol_type_print(const struct expr *expr,
 	integer_type_print(expr, octx);
 }
 
+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)
+			continue;
+
+		nft_print(octx, "\t%-30s\t%u\n", p->p_name, protonum);
+	}
+}
+
 static struct error_record *inet_protocol_type_parse(struct parse_ctx *ctx,
 						     const struct expr *sym,
 						     struct expr **res)
@@ -658,6 +672,7 @@ const struct datatype inet_protocol_type = {
 	.print		= inet_protocol_type_print,
 	.json		= inet_protocol_type_json,
 	.parse		= inet_protocol_type_parse,
+	.describe	= inet_protocol_type_describe,
 };
 
 static void inet_service_print(const struct expr *expr, struct output_ctx *octx)
diff --git a/src/expression.c b/src/expression.c
index 0c5276d1..9fdf23d9 100644
--- a/src/expression.c
+++ b/src/expression.c
@@ -172,6 +172,8 @@ void expr_describe(const struct expr *expr, struct output_ctx *octx)
 			nft_print(octx, "(in hexadecimal):\n");
 		symbol_table_print(edtype->sym_tbl, edtype,
 				   expr->byteorder, octx);
+	} else if (edtype->describe) {
+		edtype->describe(octx);
 	}
 }