packet: add a new parsing helper to parse ICMP/ICMPv6

Adds a new parsing helper which parses the beginning of an ICMP or ICMPv6
header and returns the same structure in both cases. This can be used to parse
ICMP in protocol-independent way if we are not interested in the rest of the
header.

Signed-off-by: Anton Protopopov <a.s.protopopov@gmail.com>

Author: aspsk

common/parsing_helpers.h

@@ -42,6 +42,16 @@ struct vlan_hdr {
 	__be16	h_vlan_encapsulated_proto;
 };
 
+/*
+ * Struct icmphdr_common represents the common part of the icmphdr and icmp6hdr
+ * structures.
+ */
+struct icmphdr_common {
+	__u8		type;
+	__u8		code;
+	__sum16		cksum;
+};
+
 #define VLAN_MAX_DEPTH 5
 
 static __always_inline int proto_is_vlan(__u16 h_proto)
@@ -160,6 +170,21 @@ static __always_inline int parse_icmphdr(struct hdr_cursor *nh,
 	return icmph->type;
 }
 
+static __always_inline int parse_icmphdr_common(struct hdr_cursor *nh,
+						void *data_end,
+						struct icmphdr_common **icmphdr)
+{
+	struct icmphdr_common *h = nh->pos;
+
+	if (h + 1 > data_end)
+		return -1;
+
+	nh->pos  = h + 1;
+	*icmphdr = h;
+
+	return h->type;
+}
+
 static __always_inline struct ethhdr *get_ethhdr(struct hdr_cursor *nh,
 						 void *data_end)
 {

packet-solutions/xdp_prog_kern.c

@@ -77,7 +77,7 @@ int xdp_icmp_echo_func(struct xdp_md *ctx)
 	struct iphdr *iphdr;
 	struct ipv6hdr *ipv6hdr;
 	__u16 echo_reply, m0, m1;
-	struct icmphdr *icmphdr;
+	struct icmphdr_common *icmphdr;
 	__u32 action = XDP_PASS;
 
 	/* These keep track of the next header type and iterator pointer */
@@ -97,7 +97,13 @@ int xdp_icmp_echo_func(struct xdp_md *ctx)
 		goto out;
 	}
 
-	icmp_type = parse_icmphdr(&nh, data_end, &icmphdr);
+	/*
+	 * We are using a special parser here which returns a stucture
+	 * containing the "protocol-independent" part of an ICMP or ICMPv6
+	 * header.  For purposes of this Assignment we are not interested in
+	 * the rest of the structure.
+	 */
+	icmp_type = parse_icmphdr_common(&nh, data_end, &icmphdr);
 	if (eth_type == ETH_P_IP && icmp_type == ICMP_ECHO) {
 		/* Swap IP source and destination */
 		swap_src_dst_ipv4(iphdr);

packet03-redirecting/xdp_prog_kern.c

@@ -58,7 +58,7 @@ int xdp_icmp_echo_func(struct xdp_md *ctx)
 	struct iphdr *iphdr;
 	struct ipv6hdr *ipv6hdr;
 	__u16 echo_reply;
-	struct icmphdr *icmphdr;
+	struct icmphdr_common *icmphdr;
 	__u32 action = XDP_PASS;
 
 	/* These keep track of the next header type and iterator pointer */
@@ -78,7 +78,13 @@ int xdp_icmp_echo_func(struct xdp_md *ctx)
 		goto out;
 	}
 
-	icmp_type = parse_icmphdr(&nh, data_end, &icmphdr);
+	/*
+	 * We are using a special parser here which returns a stucture
+	 * containing the "protocol-independent" part of an ICMP or ICMPv6
+	 * header.  For purposes of this Assignment we are not interested in
+	 * the rest of the structure.
+	 */
+	icmp_type = parse_icmphdr_common(&nh, data_end, &icmphdr);
 	if (eth_type == ETH_P_IP && icmp_type == ICMP_ECHO) {
 		/* Swap IP source and destination */
 		swap_src_dst_ipv4(iphdr);