Implement buffer size checking in ipfw(8) add cmd.

PR:		bin/65961
Submitted by:	Eugene Grosbein <eugen@grosbein.pp.ru>
MFC after:	2 weeks

3 files changed, 125 insertions, 62 deletions

diff --git a/sbin/ipfw/ipfw2.c b/sbin/ipfw/ipfw2.c
index 71b9e06..5d79ece 100644
--- a/sbin/ipfw/ipfw2.c
+++ b/sbin/ipfw/ipfw2.c
@@ -64,6 +64,22 @@ int ipfw_socket = -1;
 #define s6_addr32 __u6_addr.__u6_addr32
 #endif
 
+#define	CHECK_LENGTH(v, len) do {				\
+	if ((v) < (len))					\
+		errx(EX_DATAERR, "Rule too long");		\
+	} while (0)
+/*
+ * Check if we have enough space in cmd buffer. Note that since
+ * first 8? u32 words are reserved by reserved header, full cmd
+ * buffer can't be used, so we need to protect from buffer overrun
+ * only. At the beginnig, cblen is less than actual buffer size by
+ * size of ipfw_insn_u32 instruction + 1 u32 work. This eliminates need
+ * for checking small instructions fitting in given range.
+ * We also (ab)use the fact that ipfw_insn is always the first field
+ * for any custom instruction.
+ */
+#define	CHECK_CMDLEN	CHECK_LENGTH(cblen, F_LEN((ipfw_insn *)cmd))
+
 #define GET_UINT_ARG(arg, min, max, tok, s_x) do {			\
 	if (!av[0])							\
 		errx(EX_USAGE, "%s: missing argument", match_value(s_x, tok)); \
@@ -653,7 +669,7 @@ strtoport(char *s, char **end, int base, int proto)
  * Fill the body of the command with the list of port ranges.
  */
 static int
-fill_newports(ipfw_insn_u16 *cmd, char *av, int proto)
+fill_newports(ipfw_insn_u16 *cmd, char *av, int proto, int cblen)
 {
 	uint16_t a, b, *p = cmd->ports;
 	int i = 0;
@@ -664,6 +680,8 @@ fill_newports(ipfw_insn_u16 *cmd, char *av, int proto)
 		if (s == av) 			/* empty or invalid argument */
 			return (0);
 
+		CHECK_LENGTH(cblen, i + 2);
+
 		switch (*s) {
 		case '-':			/* a range */
 			av = s + 1;
@@ -2068,7 +2086,7 @@ lookup_host (char *host, struct in_addr *ipaddr)
  * We can have multiple comma-separated address/mask entries.
  */
 static void
-fill_ip(ipfw_insn_ip *cmd, char *av)
+fill_ip(ipfw_insn_ip *cmd, char *av, int cblen)
 {
 	int len = 0;
 	uint32_t *d = ((ipfw_insn_u32 *)cmd)->d;
@@ -2108,6 +2126,8 @@ fill_ip(ipfw_insn_ip *cmd, char *av)
 	int masklen;
 	char md, nd = '\0';
 
+	CHECK_LENGTH(cblen, F_INSN_SIZE(ipfw_insn) + 2 + len);
+
 	if (p) {
 		md = *p;
 		*p++ = '\0';
@@ -2366,11 +2386,13 @@ ipfw_delete(char *av[])
  * patterns which match interfaces.
  */
 static void
-fill_iface(ipfw_insn_if *cmd, char *arg)
+fill_iface(ipfw_insn_if *cmd, char *arg, int cblen)
 {
 	cmd->name[0] = '\0';
 	cmd->o.len |= F_INSN_SIZE(ipfw_insn_if);
 
+	CHECK_CMDLEN;
+
 	/* Parse the interface or address */
 	if (strcmp(arg, "any") == 0)
 		cmd->o.len = 0;		/* effectively ignore this command */
@@ -2441,8 +2463,10 @@ get_mac_addr_mask(const char *p, uint8_t *addr, uint8_t *mask)
  * the new command in case it has been clobbered before.
  */
 static ipfw_insn *
-next_cmd(ipfw_insn *cmd)
+next_cmd(ipfw_insn *cmd, int *len)
 {
+	*len -= F_LEN(cmd);
+	CHECK_LENGTH(*len, 0);
 	cmd += F_LEN(cmd);
 	bzero(cmd, sizeof(*cmd));
 	return cmd;
@@ -2452,7 +2476,7 @@ next_cmd(ipfw_insn *cmd)
  * Takes arguments and copies them into a comment
  */
 static void
-fill_comment(ipfw_insn *cmd, char **av)
+fill_comment(ipfw_insn *cmd, char **av, int cblen)
 {
 	int i, l;
 	char *p = (char *)(cmd + 1);
@@ -2470,6 +2494,8 @@ fill_comment(ipfw_insn *cmd, char **av)
 		    "comment too long (max 80 chars)");
 	l = 1 + (l+3)/4;
 	cmd->len =  (cmd->len & (F_NOT | F_OR)) | l;
+	CHECK_CMDLEN;
+
 	for (i = 0; av[i] != NULL; i++) {
 		strcpy(p, av[i]);
 		p += strlen(av[i]);
@@ -2495,7 +2521,7 @@ fill_cmd(ipfw_insn *cmd, enum ipfw_opcodes opcode, int flags, uint16_t arg)
  * two microinstructions, and returns the pointer to the last one.
  */
 static ipfw_insn *
-add_mac(ipfw_insn *cmd, char *av[])
+add_mac(ipfw_insn *cmd, char *av[], int cblen)
 {
 	ipfw_insn_mac *mac;
 
@@ -2504,6 +2530,7 @@ add_mac(ipfw_insn *cmd, char *av[])
 
 	cmd->opcode = O_MACADDR2;
 	cmd->len = (cmd->len & (F_NOT | F_OR)) | F_INSN_SIZE(ipfw_insn_mac);
+	CHECK_CMDLEN;
 
 	mac = (ipfw_insn_mac *)cmd;
 	get_mac_addr_mask(av[0], mac->addr, mac->mask);	/* dst */
@@ -2513,12 +2540,13 @@ add_mac(ipfw_insn *cmd, char *av[])
 }
 
 static ipfw_insn *
-add_mactype(ipfw_insn *cmd, char *av)
+add_mactype(ipfw_insn *cmd, char *av, int cblen)
 {
 	if (!av)
 		errx(EX_DATAERR, "missing MAC type");
 	if (strcmp(av, "any") != 0) { /* we have a non-null type */
-		fill_newports((ipfw_insn_u16 *)cmd, av, IPPROTO_ETHERTYPE);
+		fill_newports((ipfw_insn_u16 *)cmd, av, IPPROTO_ETHERTYPE,
+		    cblen);
 		cmd->opcode = O_MAC_TYPE;
 		return cmd;
 	} else
@@ -2587,9 +2615,9 @@ add_proto_compat(ipfw_insn *cmd, char *av, u_char *protop)
 }
 
 static ipfw_insn *
-add_srcip(ipfw_insn *cmd, char *av)
+add_srcip(ipfw_insn *cmd, char *av, int cblen)
 {
-	fill_ip((ipfw_insn_ip *)cmd, av);
+	fill_ip((ipfw_insn_ip *)cmd, av, cblen);
 	if (cmd->opcode == O_IP_DST_SET)			/* set */
 		cmd->opcode = O_IP_SRC_SET;
 	else if (cmd->opcode == O_IP_DST_LOOKUP)		/* table */
@@ -2604,9 +2632,9 @@ add_srcip(ipfw_insn *cmd, char *av)
 }
 
 static ipfw_insn *
-add_dstip(ipfw_insn *cmd, char *av)
+add_dstip(ipfw_insn *cmd, char *av, int cblen)
 {
-	fill_ip((ipfw_insn_ip *)cmd, av);
+	fill_ip((ipfw_insn_ip *)cmd, av, cblen);
 	if (cmd->opcode == O_IP_DST_SET)			/* set */
 		;
 	else if (cmd->opcode == O_IP_DST_LOOKUP)		/* table */
@@ -2621,12 +2649,12 @@ add_dstip(ipfw_insn *cmd, char *av)
 }
 
 static ipfw_insn *
-add_ports(ipfw_insn *cmd, char *av, u_char proto, int opcode)
+add_ports(ipfw_insn *cmd, char *av, u_char proto, int opcode, int cblen)
 {
 	/* XXX "any" is trapped before. Perhaps "to" */
 	if (_substrcmp(av, "any") == 0) {
 		return NULL;
-	} else if (fill_newports((ipfw_insn_u16 *)cmd, av, proto)) {
+	} else if (fill_newports((ipfw_insn_u16 *)cmd, av, proto, cblen)) {
 		/* XXX todo: check that we have a protocol with ports */
 		cmd->opcode = opcode;
 		return cmd;
@@ -2635,7 +2663,7 @@ add_ports(ipfw_insn *cmd, char *av, u_char proto, int opcode)
 }
 
 static ipfw_insn *
-add_src(ipfw_insn *cmd, char *av, u_char proto)
+add_src(ipfw_insn *cmd, char *av, u_char proto, int cblen)
 {
 	struct in6_addr a;
 	char *host, *ch;
@@ -2648,11 +2676,11 @@ add_src(ipfw_insn *cmd, char *av, u_char proto)
 
 	if (proto == IPPROTO_IPV6  || strcmp(av, "me6") == 0 ||
 	    inet_pton(AF_INET6, host, &a) == 1)
-		ret = add_srcip6(cmd, av);
+		ret = add_srcip6(cmd, av, cblen);
 	/* XXX: should check for IPv4, not !IPv6 */
 	if (ret == NULL && (proto == IPPROTO_IP || strcmp(av, "me") == 0 ||
 	    inet_pton(AF_INET6, host, &a) != 1))
-		ret = add_srcip(cmd, av);
+		ret = add_srcip(cmd, av, cblen);
 	if (ret == NULL && strcmp(av, "any") != 0)
 		ret = cmd;
 
@@ -2661,7 +2689,7 @@ add_src(ipfw_insn *cmd, char *av, u_char proto)
 }
 
 static ipfw_insn *
-add_dst(ipfw_insn *cmd, char *av, u_char proto)
+add_dst(ipfw_insn *cmd, char *av, u_char proto, int cblen)
 {
 	struct in6_addr a;
 	char *host, *ch;
@@ -2674,11 +2702,11 @@ add_dst(ipfw_insn *cmd, char *av, u_char proto)
 
 	if (proto == IPPROTO_IPV6  || strcmp(av, "me6") == 0 ||
 	    inet_pton(AF_INET6, host, &a) == 1)
-		ret = add_dstip6(cmd, av);
+		ret = add_dstip6(cmd, av, cblen);
 	/* XXX: should check for IPv4, not !IPv6 */
 	if (ret == NULL && (proto == IPPROTO_IP || strcmp(av, "me") == 0 ||
 	    inet_pton(AF_INET6, host, &a) != 1))
-		ret = add_dstip(cmd, av);
+		ret = add_dstip(cmd, av, cblen);
 	if (ret == NULL && strcmp(av, "any") != 0)
 		ret = cmd;
 
@@ -2708,6 +2736,7 @@ ipfw_add(char *av[])
 	 * go into actbuf[].
 	 */
 	static uint32_t rulebuf[255], actbuf[255], cmdbuf[255];
+	int rblen, ablen, cblen;
 
 	ipfw_insn *src, *dst, *cmd, *action, *prev=NULL;
 	ipfw_insn *first_cmd;	/* first match pattern */
@@ -2738,6 +2767,15 @@ ipfw_add(char *av[])
 	cmd = (ipfw_insn *)cmdbuf;
 	action = (ipfw_insn *)actbuf;
 
+	rblen = sizeof(rulebuf) / sizeof(rulebuf[0]);
+	rblen -= offsetof(struct ip_fw, cmd) / sizeof(rulebuf[0]);
+	ablen = sizeof(actbuf) / sizeof(actbuf[0]);
+	cblen = sizeof(cmdbuf) / sizeof(cmdbuf[0]);
+	cblen -= F_INSN_SIZE(ipfw_insn_u32) + 1;
+
+#define	CHECK_RBUFLEN(len)	{ CHECK_LENGTH(rblen, len); rblen -= len; }
+#define	CHECK_ACTLEN		CHECK_LENGTH(ablen, action->len)
+
 	av++;
 
 	/* [rule N]	-- Rule number optional */
@@ -2769,6 +2807,7 @@ ipfw_add(char *av[])
 	i = match_token(rule_actions, *av);
 	av++;
 	action->len = 1;	/* default */
+	CHECK_ACTLEN;
 	switch(i) {
 	case TOK_CHECKSTATE:
 		have_state = action;
@@ -2820,6 +2859,7 @@ ipfw_add(char *av[])
 	case TOK_NAT:
 		action->opcode = O_NAT;
 		action->len = F_INSN_SIZE(ipfw_insn_nat);
+		CHECK_ACTLEN;
 		if (_substrcmp(*av, "global") == 0) {
 			action->arg1 = 0;
 			av++;
@@ -2936,6 +2976,7 @@ chkarg:
 
 			action->opcode = O_FORWARD_IP;
 			action->len = F_INSN_SIZE(ipfw_insn_sa);
+			CHECK_ACTLEN;
 
 			/*
 			 * In the kernel we assume AF_INET and use only
@@ -2952,6 +2993,7 @@ chkarg:
 
 			action->opcode = O_FORWARD_IP6;
 			action->len = F_INSN_SIZE(ipfw_insn_sa6);
+			CHECK_ACTLEN;
 
 			p->sa.sin6_len = sizeof(struct sockaddr_in6);
 			p->sa.sin6_family = AF_INET6;
@@ -3005,7 +3047,7 @@ chkarg:
 	default:
 		errx(EX_DATAERR, "invalid action %s\n", av[-1]);
 	}
-	action = next_cmd(action);
+	action = next_cmd(action, &ablen);
 
 	/*
 	 * [altq queuename] -- altq tag, optional
@@ -3027,6 +3069,7 @@ chkarg:
 				    "log cannot be specified more than once");
 			have_log = (ipfw_insn *)c;
 			cmd->len = F_INSN_SIZE(ipfw_insn_log);
+			CHECK_CMDLEN;
 			cmd->opcode = O_LOG;
 			if (av[0] && _substrcmp(*av, "logamount") == 0) {
 				av++;
@@ -3058,6 +3101,7 @@ chkarg:
 				    "altq cannot be specified more than once");
 			have_altq = (ipfw_insn *)a;
 			cmd->len = F_INSN_SIZE(ipfw_insn_altq);
+			CHECK_CMDLEN;
 			cmd->opcode = O_ALTQ;
 			a->qid = altq_name_to_qid(*av);
 			av++;
@@ -3083,7 +3127,7 @@ chkarg:
 		default:
 			abort();
 		}
-		cmd = next_cmd(cmd);
+		cmd = next_cmd(cmd, &cblen);
 	}
 
 	if (have_state)	/* must be a check-state, we are done */
@@ -3168,7 +3212,7 @@ chkarg:
 		av++;
 		if (F_LEN(cmd) != 0) {
 			prev = cmd;
-			cmd = next_cmd(cmd);
+			cmd = next_cmd(cmd, &cblen);
 		}
 	} else if (first_cmd != cmd) {
 		errx(EX_DATAERR, "invalid protocol ``%s''", *av);
@@ -3189,11 +3233,11 @@ chkarg:
     OR_START(source_ip);
 	NOT_BLOCK;	/* optional "not" */
 	NEED1("missing source address");
-	if (add_src(cmd, *av, proto)) {
+	if (add_src(cmd, *av, proto, cblen)) {
 		av++;
 		if (F_LEN(cmd) != 0) {	/* ! any */
 			prev = cmd;
-			cmd = next_cmd(cmd);
+			cmd = next_cmd(cmd, &cblen);
 		}
 	} else
 		errx(EX_USAGE, "bad source address %s", *av);
@@ -3205,10 +3249,10 @@ chkarg:
 	NOT_BLOCK;	/* optional "not" */
 	if ( av[0] != NULL ) {
 		if (_substrcmp(*av, "any") == 0 ||
-		    add_ports(cmd, *av, proto, O_IP_SRCPORT)) {
+		    add_ports(cmd, *av, proto, O_IP_SRCPORT, cblen)) {
 			av++;
 			if (F_LEN(cmd) != 0)
-				cmd = next_cmd(cmd);
+				cmd = next_cmd(cmd, &cblen);
 		}
 	}
 
@@ -3225,11 +3269,11 @@ chkarg:
     OR_START(dest_ip);
 	NOT_BLOCK;	/* optional "not" */
 	NEED1("missing dst address");
-	if (add_dst(cmd, *av, proto)) {
+	if (add_dst(cmd, *av, proto, cblen)) {
 		av++;
 		if (F_LEN(cmd) != 0) {	/* ! any */
 			prev = cmd;
-			cmd = next_cmd(cmd);
+			cmd = next_cmd(cmd, &cblen);
 		}
 	} else
 		errx( EX_USAGE, "bad destination address %s", *av);
@@ -3241,10 +3285,10 @@ chkarg:
 	NOT_BLOCK;	/* optional "not" */
 	if (av[0]) {
 		if (_substrcmp(*av, "any") == 0 ||
-		    add_ports(cmd, *av, proto, O_IP_DSTPORT)) {
+		    add_ports(cmd, *av, proto, O_IP_DSTPORT, cblen)) {
 			av++;
 			if (F_LEN(cmd) != 0)
-				cmd = next_cmd(cmd);
+				cmd = next_cmd(cmd, &cblen);
 		}
 	}
 
@@ -3332,7 +3376,7 @@ read_options:
 		case TOK_VIA:
 			NEED1("recv, xmit, via require interface name"
 				" or address");
-			fill_iface((ipfw_insn_if *)cmd, av[0]);
+			fill_iface((ipfw_insn_if *)cmd, av[0], cblen);
 			av++;
 			if (F_LEN(cmd) == 0)	/* not a valid address */
 				break;
@@ -3352,14 +3396,14 @@ read_options:
 
 		case TOK_ICMP6TYPES:
 			NEED1("icmptypes requires list of types");
-			fill_icmp6types((ipfw_insn_icmp6 *)cmd, *av);
+			fill_icmp6types((ipfw_insn_icmp6 *)cmd, *av, cblen);
 			av++;
 			break;
 
 		case TOK_IPTTL:
 			NEED1("ipttl requires TTL");
 			if (strpbrk(*av, "-,")) {
-			    if (!add_ports(cmd, *av, 0, O_IPTTL))
+			    if (!add_ports(cmd, *av, 0, O_IPTTL, cblen))
 				errx(EX_DATAERR, "invalid ipttl %s", *av);
 			} else
 			    fill_cmd(cmd, O_IPTTL, 0, strtoul(*av, NULL, 0));
@@ -3369,7 +3413,7 @@ read_options:
 		case TOK_IPID:
 			NEED1("ipid requires id");
 			if (strpbrk(*av, "-,")) {
-			    if (!add_ports(cmd, *av, 0, O_IPID))
+			    if (!add_ports(cmd, *av, 0, O_IPID, cblen))
 				errx(EX_DATAERR, "invalid ipid %s", *av);
 			} else
 			    fill_cmd(cmd, O_IPID, 0, strtoul(*av, NULL, 0));
@@ -3379,7 +3423,7 @@ read_options:
 		case TOK_IPLEN:
 			NEED1("iplen requires length");
 			if (strpbrk(*av, "-,")) {
-			    if (!add_ports(cmd, *av, 0, O_IPLEN))
+			    if (!add_ports(cmd, *av, 0, O_IPLEN, cblen))
 				errx(EX_DATAERR, "invalid ip len %s", *av);
 			} else
 			    fill_cmd(cmd, O_IPLEN, 0, strtoul(*av, NULL, 0));
@@ -3475,7 +3519,7 @@ read_options:
 		case TOK_TCPDATALEN:
 			NEED1("tcpdatalen requires length");
 			if (strpbrk(*av, "-,")) {
-			    if (!add_ports(cmd, *av, 0, O_TCPDATALEN))
+			    if (!add_ports(cmd, *av, 0, O_TCPDATALEN, cblen))
 				errx(EX_DATAERR, "invalid tcpdata len %s", *av);
 			} else
 			    fill_cmd(cmd, O_TCPDATALEN, 0,
@@ -3501,7 +3545,7 @@ read_options:
 		case TOK_TCPWIN:
 			NEED1("tcpwin requires length");
 			if (strpbrk(*av, "-,")) {
-			    if (!add_ports(cmd, *av, 0, O_TCPWIN))
+			    if (!add_ports(cmd, *av, 0, O_TCPWIN, cblen))
 				errx(EX_DATAERR, "invalid tcpwin len %s", *av);
 			} else
 			    fill_cmd(cmd, O_TCPWIN, 0,
@@ -3540,6 +3584,7 @@ read_options:
 			have_state = cmd;
 
 			cmd->len = F_INSN_SIZE(ipfw_insn_limit);
+			CHECK_CMDLEN;
 			cmd->opcode = O_LIMIT;
 			c->limit_mask = c->conn_limit = 0;
 
@@ -3571,28 +3616,28 @@ read_options:
 
 		case TOK_SRCIP:
 			NEED1("missing source IP");
-			if (add_srcip(cmd, *av)) {
+			if (add_srcip(cmd, *av, cblen)) {
 				av++;
 			}
 			break;
 
 		case TOK_DSTIP:
 			NEED1("missing destination IP");
-			if (add_dstip(cmd, *av)) {
+			if (add_dstip(cmd, *av, cblen)) {
 				av++;
 			}
 			break;
 
 		case TOK_SRCIP6:
 			NEED1("missing source IP6");
-			if (add_srcip6(cmd, *av)) {
+			if (add_srcip6(cmd, *av, cblen)) {
 				av++;
 			}
 			break;
 
 		case TOK_DSTIP6:
 			NEED1("missing destination IP6");
-			if (add_dstip6(cmd, *av)) {
+			if (add_dstip6(cmd, *av, cblen)) {
 				av++;
 			}
 			break;
@@ -3600,7 +3645,7 @@ read_options:
 		case TOK_SRCPORT:
 			NEED1("missing source port");
 			if (_substrcmp(*av, "any") == 0 ||
-			    add_ports(cmd, *av, proto, O_IP_SRCPORT)) {
+			    add_ports(cmd, *av, proto, O_IP_SRCPORT, cblen)) {
 				av++;
 			} else
 				errx(EX_DATAERR, "invalid source port %s", *av);
@@ -3609,7 +3654,7 @@ read_options:
 		case TOK_DSTPORT:
 			NEED1("missing destination port");
 			if (_substrcmp(*av, "any") == 0 ||
-			    add_ports(cmd, *av, proto, O_IP_DSTPORT)) {
+			    add_ports(cmd, *av, proto, O_IP_DSTPORT, cblen)) {
 				av++;
 			} else
 				errx(EX_DATAERR, "invalid destination port %s",
@@ -3617,13 +3662,13 @@ read_options:
 			break;
 
 		case TOK_MAC:
-			if (add_mac(cmd, av))
+			if (add_mac(cmd, av, cblen))
 				av += 2;
 			break;
 
 		case TOK_MACTYPE:
 			NEED1("missing mac type");
-			if (!add_mactype(cmd, *av))
+			if (!add_mactype(cmd, *av, cblen))
 				errx(EX_DATAERR, "invalid mac type %s", *av);
 			av++;
 			break;
@@ -3661,18 +3706,18 @@ read_options:
 			if (proto != IPPROTO_IPV6 )
 				errx( EX_USAGE, "flow-id filter is active "
 				    "only for ipv6 protocol\n");
-			fill_flow6( (ipfw_insn_u32 *) cmd, *av );
+			fill_flow6( (ipfw_insn_u32 *) cmd, *av, cblen);
 			av++;
 			break;
 
 		case TOK_COMMENT:
-			fill_comment(cmd, av);
+			fill_comment(cmd, av, cblen);
 			av[0]=NULL;
 			break;
 
 		case TOK_TAGGED:
 			if (av[0] && strpbrk(*av, "-,")) {
-				if (!add_ports(cmd, *av, 0, O_TAGGED))
+				if (!add_ports(cmd, *av, 0, O_TAGGED, cblen))
 					errx(EX_DATAERR, "tagged: invalid tag"
 					    " list: %s", *av);
 			}
@@ -3725,7 +3770,7 @@ read_options:
 		}
 		if (F_LEN(cmd) > 0) {	/* prepare to advance */
 			prev = cmd;
-			cmd = next_cmd(cmd);
+			cmd = next_cmd(cmd, &cblen);
 		}
 	}
 
@@ -3754,12 +3799,13 @@ done:
 	 */
 	if (have_state && have_state->opcode != O_CHECK_STATE) {
 		fill_cmd(dst, O_PROBE_STATE, 0, 0);
-		dst = next_cmd(dst);
+		dst = next_cmd(dst, &rblen);
 	}
 
 	/* copy all commands but O_LOG, O_KEEP_STATE, O_LIMIT, O_ALTQ, O_TAG */
 	for (src = (ipfw_insn *)cmdbuf; src != cmd; src += i) {
 		i = F_LEN(src);
+		CHECK_RBUFLEN(i);
 
 		switch (src->opcode) {
 		case O_LOG:
@@ -3779,6 +3825,7 @@ done:
 	 */
 	if (have_state && have_state->opcode != O_CHECK_STATE) {
 		i = F_LEN(have_state);
+		CHECK_RBUFLEN(i);
 		bcopy(have_state, dst, i * sizeof(uint32_t));
 		dst += i;
 	}
@@ -3790,24 +3837,29 @@ done:
 	/* put back O_LOG, O_ALTQ, O_TAG if necessary */
 	if (have_log) {
 		i = F_LEN(have_log);
+		CHECK_RBUFLEN(i);
 		bcopy(have_log, dst, i * sizeof(uint32_t));
 		dst += i;
 	}
 	if (have_altq) {
 		i = F_LEN(have_altq);
+		CHECK_RBUFLEN(i);
 		bcopy(have_altq, dst, i * sizeof(uint32_t));
 		dst += i;
 	}
 	if (have_tag) {
 		i = F_LEN(have_tag);
+		CHECK_RBUFLEN(i);
 		bcopy(have_tag, dst, i * sizeof(uint32_t));
 		dst += i;
 	}
+
 	/*
 	 * copy all other actions
 	 */
 	for (src = (ipfw_insn *)actbuf; src != action; src += i) {
 		i = F_LEN(src);
+		CHECK_RBUFLEN(i);
 		bcopy(src, dst, i * sizeof(uint32_t));
 		dst += i;
 	}
diff --git a/sbin/ipfw/ipfw2.h b/sbin/ipfw/ipfw2.h
index bade0dd..81e0ba8 100644
--- a/sbin/ipfw/ipfw2.h
+++ b/sbin/ipfw/ipfw2.h
@@ -283,10 +283,10 @@ void print_flow6id(struct _ipfw_insn_u32 *cmd);
 void print_icmp6types(struct _ipfw_insn_u32 *cmd);
 void print_ext6hdr(struct _ipfw_insn *cmd );
 
-struct _ipfw_insn *add_srcip6(struct _ipfw_insn *cmd, char *av);
-struct _ipfw_insn *add_dstip6(struct _ipfw_insn *cmd, char *av);
+struct _ipfw_insn *add_srcip6(struct _ipfw_insn *cmd, char *av, int cblen);
+struct _ipfw_insn *add_dstip6(struct _ipfw_insn *cmd, char *av, int cblen);
 
-void fill_flow6(struct _ipfw_insn_u32 *cmd, char *av );
+void fill_flow6(struct _ipfw_insn_u32 *cmd, char *av, int cblen);
 void fill_unreach6_code(u_short *codep, char *str);
-void fill_icmp6types(struct _ipfw_insn_icmp6 *cmd, char *av);
+void fill_icmp6types(struct _ipfw_insn_icmp6 *cmd, char *av, int cblen);
 int fill_ext6hdr(struct _ipfw_insn *cmd, char *av);
diff --git a/sbin/ipfw/ipv6.c b/sbin/ipfw/ipv6.c
index 6326590..ee9bb62 100644
--- a/sbin/ipfw/ipv6.c
+++ b/sbin/ipfw/ipv6.c
@@ -42,6 +42,11 @@
 #include <netinet/ip_fw.h>
 #include <arpa/inet.h>
 
+#define	CHECK_LENGTH(v, len) do {			\
+	if ((v) < (len))				\
+		errx(EX_DATAERR, "Rule too long");	\
+	} while (0)
+
 static struct _s_x icmp6codes[] = {
       { "no-route",		ICMP6_DST_UNREACH_NOROUTE },
       { "admin-prohib",		ICMP6_DST_UNREACH_ADMIN },
@@ -131,10 +136,12 @@ print_ip6(ipfw_insn_ip6 *cmd, char const *s)
 }
 
 void
-fill_icmp6types(ipfw_insn_icmp6 *cmd, char *av)
+fill_icmp6types(ipfw_insn_icmp6 *cmd, char *av, int cblen)
 {
        uint8_t type;
 
+       CHECK_LENGTH(cblen, F_INSN_SIZE(ipfw_insn_icmp6));
+
        bzero(cmd, sizeof(*cmd));
        while (*av) {
 	   if (*av == ',')
@@ -327,7 +334,7 @@ lookup_host6 (char *host, struct in6_addr *ip6addr)
  * Return 1 on success, 0 on failure.
  */
 static int
-fill_ip6(ipfw_insn_ip6 *cmd, char *av)
+fill_ip6(ipfw_insn_ip6 *cmd, char *av, int cblen)
 {
 	int len = 0;
 	struct in6_addr *d = &(cmd->addr6);
@@ -379,6 +386,8 @@ fill_ip6(ipfw_insn_ip6 *cmd, char *av)
 		int masklen;
 		char md = '\0';
 
+		CHECK_LENGTH(cblen, 1 + len + 2 * F_INSN_SIZE(struct in6_addr));
+
 		if ((p = strpbrk(av, "/,")) ) {
 			md = *p;	/* save the separator */
 			*p = '\0';	/* terminate address string */
@@ -453,7 +462,7 @@ fill_ip6(ipfw_insn_ip6 *cmd, char *av)
  * additional flow-id we want to filter, the basic is 1
  */
 void
-fill_flow6( ipfw_insn_u32 *cmd, char *av )
+fill_flow6( ipfw_insn_u32 *cmd, char *av, int cblen)
 {
 	u_int32_t type;	 /* Current flow number */
 	u_int16_t nflow = 0;    /* Current flow index */
@@ -461,6 +470,8 @@ fill_flow6( ipfw_insn_u32 *cmd, char *av )
 	cmd->d[0] = 0;	  /* Initializing the base number*/
 
 	while (s) {
+		CHECK_LENGTH(cblen, F_INSN_SIZE(ipfw_insn_u32) + nflow + 1);
+
 		av = strsep( &s, ",") ;
 		type = strtoul(av, &av, 0);
 		if (*av != ',' && *av != '\0')
@@ -481,10 +492,10 @@ fill_flow6( ipfw_insn_u32 *cmd, char *av )
 }
 
 ipfw_insn *
-add_srcip6(ipfw_insn *cmd, char *av)
+add_srcip6(ipfw_insn *cmd, char *av, int cblen)
 {
 
-	fill_ip6((ipfw_insn_ip6 *)cmd, av);
+	fill_ip6((ipfw_insn_ip6 *)cmd, av, cblen);
 	if (cmd->opcode == O_IP_DST_SET)			/* set */
 		cmd->opcode = O_IP_SRC_SET;
 	else if (cmd->opcode == O_IP_DST_LOOKUP)		/* table */
@@ -503,10 +514,10 @@ add_srcip6(ipfw_insn *cmd, char *av)
 }
 
 ipfw_insn *
-add_dstip6(ipfw_insn *cmd, char *av)
+add_dstip6(ipfw_insn *cmd, char *av, int cblen)
 {
 
-	fill_ip6((ipfw_insn_ip6 *)cmd, av);
+	fill_ip6((ipfw_insn_ip6 *)cmd, av, cblen);
 	if (cmd->opcode == O_IP_DST_SET)			/* set */
 		;
 	else if (cmd->opcode == O_IP_DST_LOOKUP)		/* table */