[PATCH iproute2 6/9] actions: add skbmod action

[Jamal Hadi Salim <jhs@mojatatu.com>]

From: Jamal Hadi Salim <jhs@mojatatu.com>

This action is intended to be an upgrade from a usability perspective
from pedit (as well as operational debugability).
Compare this:

sudo tc filter add dev $ETH parent 1: protocol ip prio 10 \
u32 match ip protocol 1 0xff flowid 1:2 \
action pedit munge offset -14 u8 set 0x02 \
    munge offset -13 u8 set 0x15 \
    munge offset -12 u8 set 0x15 \
    munge offset -11 u8 set 0x15 \
    munge offset -10 u16 set 0x1515 \
    pipe

to:

sudo tc filter add dev $ETH parent 1: protocol ip prio 10 \
u32 match ip protocol 1 0xff flowid 1:2 \
action skbmod dmac 02:15:15:15:15:15

Or worse, try to debug a policy with destination mac, source mac and
etherype. Then make that a hundred rules and you'll get my point.

The most important ethernet use case at the moment is when redirecting or
mirroring packets to a remote machine. The dst mac address needs a re-write
so that it doesnt get dropped or confuse an interconnecting (learning) switch
or dropped by a target machine (which looks at the dst mac).

In the future common use cases on pedit can be migrated to this action
(as an example different fields in ip v4/6, transports like tcp/udp/sctp
etc). For this first cut, this allows modifying basic ethernet header.

Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
---
 tc/Makefile   |   1 +
 tc/m_skbmod.c | 270 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 271 insertions(+)
 create mode 100644 tc/m_skbmod.c

diff --git a/tc/Makefile b/tc/Makefile
index 8917eaf..e2f340c 100644
--- a/tc/Makefile
+++ b/tc/Makefile
@@ -45,6 +45,7 @@ TCMODULES += m_nat.o
 TCMODULES += m_pedit.o
 TCMODULES += m_ife.o
 TCMODULES += m_skbedit.o
+TCMODULES += m_skbmod.o
 TCMODULES += m_csum.o
 TCMODULES += m_simple.o
 TCMODULES += m_vlan.o
diff --git a/tc/m_skbmod.c b/tc/m_skbmod.c
new file mode 100644
index 0000000..38c83a2
--- /dev/null
+++ b/tc/m_skbmod.c
@@ -0,0 +1,270 @@
+/*
+ * m_skbmod.c	skb modifier action module
+ *
+ *		This program is free software; you can distribute it and/or
+ *		modify it under the terms of the GNU General Public License
+ *		as published by the Free Software Foundation; either version
+ *		2 of the License, or (at your option) any later version.
+ *
+ * Authors:  J Hadi Salim (jhs@mojatatu.com)
+ *
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <syslog.h>
+#include <fcntl.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+#include <string.h>
+#include <linux/netdevice.h>
+
+#include "rt_names.h"
+#include "utils.h"
+#include "tc_util.h"
+#include <linux/tc_act/tc_skbmod.h>
+
+static void skbmod_explain(void)
+{
+	fprintf(stderr,
+		"Usage:... skbmod {[set <SETTABLE>] [swap <SWAPABLE>]} [CONTROL] [index INDEX]\n");
+	fprintf(stderr, "where SETTABLE is: [dmac DMAC] [smac SMAC] [etype ETYPE] \n");
+	fprintf(stderr, "where SWAPABLE is: \"mac\" to swap mac addresses\n");
+	fprintf(stderr, "note: \"swap mac\" is done after any outstanding D/SMAC change\n");
+	fprintf(stderr,
+		"\tDMAC := 6 byte Destination MAC address\n"
+		"\tSMAC := optional 6 byte Source MAC address\n"
+		"\tETYPE := optional 16 bit ethertype\n"
+		"\tCONTROL := reclassify|pipe|drop|continue|ok\n"
+		"\tINDEX := skbmod index value to use\n");
+}
+
+static void skbmod_usage(void)
+{
+	skbmod_explain();
+	exit(-1);
+}
+
+static int parse_skbmod(struct action_util *a, int *argc_p, char ***argv_p,
+			int tca_id, struct nlmsghdr *n)
+{
+	int argc = *argc_p;
+	char **argv = *argv_p;
+	int ok = 0;
+	struct tc_skbmod p;
+	struct rtattr *tail;
+	char dbuf[ETH_ALEN];
+	char sbuf[ETH_ALEN];
+	__u16 skbmod_etype = 0;
+	char *daddr = NULL;
+	char *saddr = NULL;
+
+	memset(&p, 0, sizeof(p));
+	p.action = TC_ACT_PIPE;	/* good default */
+
+	if (argc <= 0)
+		return -1;
+
+	while (argc > 0) {
+		if (matches(*argv, "skbmod") == 0) {
+			NEXT_ARG();
+			continue;
+		} else if (matches(*argv, "swap") == 0) {
+			NEXT_ARG();
+			continue;
+		} else if (matches(*argv, "mac") == 0) {
+			p.flags |= SKBMOD_F_SWAPMAC;
+			ok +=1;
+		} else if (matches(*argv, "set") == 0) {
+			NEXT_ARG();
+			continue;
+		} else if (matches(*argv, "etype") == 0) {
+			NEXT_ARG();
+			if (get_u16(&skbmod_etype, *argv, 0))
+				invarg("ethertype is invalid", *argv);
+			fprintf(stderr, "skbmod etype 0x%x\n", skbmod_etype);
+			p.flags |= SKBMOD_F_ETYPE;
+			ok +=1;
+		} else if (matches(*argv, "dmac") == 0) {
+			NEXT_ARG();
+			daddr = *argv;
+			if (sscanf(daddr, "%hhx:%hhx:%hhx:%hhx:%hhx:%hhx",
+				   dbuf, dbuf + 1, dbuf + 2,
+				   dbuf + 3, dbuf + 4, dbuf + 5) != 6) {
+				fprintf(stderr, "Invalid dst mac address %s\n",
+					daddr);
+				return -1;
+			}
+			p.flags |= SKBMOD_F_DMAC;
+			fprintf(stderr, "dst MAC address <%s>\n", daddr);
+			ok +=1;
+
+		} else if (matches(*argv, "smac") == 0) {
+			NEXT_ARG();
+			saddr = *argv;
+			if (sscanf(saddr, "%hhx:%hhx:%hhx:%hhx:%hhx:%hhx",
+				   sbuf, sbuf + 1, sbuf + 2,
+				   sbuf + 3, sbuf + 4, sbuf + 5) != 6) {
+				fprintf(stderr, "Invalid smac address %s\n",
+					saddr);
+				return -1;
+			}
+			p.flags |= SKBMOD_F_SMAC;
+			fprintf(stderr, "src MAC address <%s>\n", saddr);
+			ok +=1;
+		} else if (matches(*argv, "help") == 0) {
+			skbmod_usage();
+		} else {
+			break;
+		}
+
+		argc--;
+		argv++;
+	}
+
+#if 0
+	if (p.flags & SKBMOD_F_SWAPMAC) {
+		if ((p.flags & SKBMOD_F_DMAC) || (p.flags & SKBMOD_F_SMAC)) {
+			fprintf(stderr, "Not allowed to mix S/MAC and swapping\n");
+			skbmod_usage();
+		}
+	}
+#endif
+
+	if (argc) {
+		if (matches(*argv, "reclassify") == 0) {
+			p.action = TC_ACT_RECLASSIFY;
+			argc--;
+			argv++;
+		} else if (matches(*argv, "pipe") == 0) {
+			p.action = TC_ACT_PIPE;
+			argc--;
+			argv++;
+		} else if (matches(*argv, "drop") == 0 ||
+			   matches(*argv, "shot") == 0) {
+			p.action = TC_ACT_SHOT;
+			argc--;
+			argv++;
+		} else if (matches(*argv, "continue") == 0) {
+			p.action = TC_ACT_UNSPEC;
+			argc--;
+			argv++;
+		} else if (matches(*argv, "pass") == 0 ||
+			   matches(*argv, "ok") == 0) {
+			p.action = TC_ACT_OK;
+			argc--;
+			argv++;
+		}
+	}
+
+	if (argc) {
+		if (matches(*argv, "index") == 0) {
+			NEXT_ARG();
+			if (get_u32(&p.index, *argv, 0)) {
+				fprintf(stderr, "skbmod: Illegal \"index\"\n");
+				return -1;
+			}
+			ok++;
+			argc--;
+			argv++;
+		}
+	}
+
+	if (!ok) {
+		fprintf(stderr, "skbmod requires at least one option\n");
+		skbmod_usage();
+	}
+
+	tail = NLMSG_TAIL(n);
+	addattr_l(n, MAX_MSG, tca_id, NULL, 0);
+	addattr_l(n, MAX_MSG, TCA_SKBMOD_PARMS, &p, sizeof(p));
+
+	if (daddr)
+		addattr_l(n, MAX_MSG, TCA_SKBMOD_DMAC, dbuf, ETH_ALEN);
+	if (skbmod_etype)
+		addattr16(n, MAX_MSG, TCA_SKBMOD_ETYPE, skbmod_etype);
+	if (saddr)
+		addattr_l(n, MAX_MSG, TCA_SKBMOD_SMAC, sbuf, ETH_ALEN);
+
+	tail->rta_len = (void *)NLMSG_TAIL(n) - (void *)tail;
+
+	*argc_p = argc;
+	*argv_p = argv;
+	return 0;
+}
+
+static int print_skbmod(struct action_util *au, FILE *f, struct rtattr *arg)
+{
+	struct tc_skbmod *p = NULL;
+	struct rtattr *tb[TCA_SKBMOD_MAX + 1];
+	__u16 skbmod_etype = 0;
+	int has_optional = 0;
+        SPRINT_BUF(b1);
+        SPRINT_BUF(b2);
+
+	if (arg == NULL)
+		return -1;
+
+	parse_rtattr_nested(tb, TCA_SKBMOD_MAX, arg);
+
+	if (tb[TCA_SKBMOD_PARMS] == NULL) {
+		fprintf(f, "[NULL skbmod parameters]");
+		return -1;
+	}
+
+	p = RTA_DATA(tb[TCA_SKBMOD_PARMS]);
+
+	fprintf(f, "skbmod action %s ", action_n2a(p->action));
+
+	if (tb[TCA_SKBMOD_ETYPE]) {
+		skbmod_etype = rta_getattr_u16(tb[TCA_SKBMOD_ETYPE]);
+		has_optional = 1;
+		fprintf(f, "set etype 0x%X ", skbmod_etype);
+	}
+
+	if (has_optional)
+		fprintf(f, "\n\t ");
+
+	if (tb[TCA_SKBMOD_DMAC]) {
+		has_optional = 1;
+		fprintf(f, "set dmac %s ",
+			ll_addr_n2a(RTA_DATA(tb[TCA_SKBMOD_DMAC]),
+				    RTA_PAYLOAD(tb[TCA_SKBMOD_DMAC]), 0, b1,
+				    sizeof(b1)));
+
+	}
+
+	if (tb[TCA_SKBMOD_SMAC]) {
+		has_optional = 1;
+		fprintf(f, "set smac %s ",
+			ll_addr_n2a(RTA_DATA(tb[TCA_SKBMOD_SMAC]),
+				    RTA_PAYLOAD(tb[TCA_SKBMOD_SMAC]), 0, b2,
+				    sizeof(b2)));
+	}
+
+	if (p->flags & SKBMOD_F_SWAPMAC) {
+		fprintf(f, "swap mac ");
+	}
+
+	fprintf(f, "\n\t index %d ref %d bind %d", p->index, p->refcnt,
+		p->bindcnt);
+	if (show_stats) {
+		if (tb[TCA_SKBMOD_TM]) {
+			struct tcf_t *tm = RTA_DATA(tb[TCA_SKBMOD_TM]);
+
+			print_tm(f, tm);
+		}
+	}
+
+	fprintf(f, "\n");
+
+	return 0;
+}
+
+struct action_util skbmod_action_util = {
+	.id = "skbmod",
+	.parse_aopt = parse_skbmod,
+	.print_aopt = print_skbmod,
+};
-- 
1.9.1