odhcpd: detect broken hostnames

Check hostnames contain valid characters as defined in RFC 952 and RFC 1123.
Invalid hostnames in uci configured host entries will result into a refusal
to create the static lease.
In case a client received hostname contains an invalid character no
<hostname> <IP address> entry will be added to the lease file.
In such case the leaseinfo description in the lease file will still contain
the hostname but preceded by the string broken\x20

Signed-off-by: Hans Dedecker <dedeckeh@gmail.com>

6 files changed, 64 insertions, 8 deletions

diff --git a/src/config.c b/src/config.c
index 6556eac..b36afb1 100644
--- a/src/config.c
+++ b/src/config.c
@@ -344,8 +344,11 @@ static int set_lease(struct uci_section *s)
 	if (!lease)
 		goto err;
 
-	if (hostlen > 1)
+	if (hostlen > 1) {
 		memcpy(lease->hostname, blobmsg_get_string(c), hostlen);
+		if (!odhcpd_valid_hostname(lease->hostname))
+			goto err;
+	}
 
 	if ((c = tb[LEASE_ATTR_IP]))
 		if (inet_pton(AF_INET, blobmsg_get_string(c), &lease->ipaddr) < 0)
diff --git a/src/dhcpv4.c b/src/dhcpv4.c
index 3386abb..2cc6278 100644
--- a/src/dhcpv4.c
+++ b/src/dhcpv4.c
@@ -1095,6 +1095,11 @@ static struct dhcpv4_assignment* dhcpv4_lease(struct interface *iface,
 					if (a->hostname) {
 						memcpy(a->hostname, hostname, hostname_len);
 						a->hostname[hostname_len] = 0;
+
+						if (odhcpd_valid_hostname(a->hostname))
+							a->flags &= ~OAF_BROKEN_HOSTNAME;
+						else
+							a->flags |= OAF_BROKEN_HOSTNAME;
 					}
 				}
 
diff --git a/src/dhcpv6-ia.c b/src/dhcpv6-ia.c
index 4ee6dd2..fb1c228 100644
--- a/src/dhcpv6-ia.c
+++ b/src/dhcpv6-ia.c
@@ -331,7 +331,8 @@ void dhcpv6_write_ia_addr(struct in6_addr *addr, int prefix, _unused uint32_t pr
 
 	inet_ntop(AF_INET6, addr, ipbuf, sizeof(ipbuf) - 1);
 
-	if (ctxt->c->length == 128 && ctxt->c->hostname) {
+	if (ctxt->c->length == 128 && ctxt->c->hostname &&
+	    !(ctxt->c->flags & OAF_BROKEN_HOSTNAME)) {
 		fputs(ipbuf, ctxt->fp);
 
 		char b[256];
@@ -394,8 +395,9 @@ void dhcpv6_write_statefile(void)
 					odhcpd_hexlify(duidbuf, ctxt.c->clid_data, ctxt.c->clid_len);
 
 					/* iface DUID iaid hostname lifetime assigned length [addrs...] */
-					ctxt.buf_idx = snprintf(ctxt.buf, ctxt.buf_len, "# %s %s %x %s %ld %x %u ",
+					ctxt.buf_idx = snprintf(ctxt.buf, ctxt.buf_len, "# %s %s %x %s%s %ld %x %u ",
 								ctxt.iface->ifname, duidbuf, ntohl(ctxt.c->iaid),
+								(ctxt.c->flags & OAF_BROKEN_HOSTNAME) ? "broken\\x20" : "",
 								(ctxt.c->hostname ? ctxt.c->hostname : "-"),
 								(ctxt.c->valid_until > now ?
 									(ctxt.c->valid_until - now + wall_time) :
@@ -423,8 +425,9 @@ void dhcpv6_write_statefile(void)
 					odhcpd_hexlify(duidbuf, c->hwaddr, sizeof(c->hwaddr));
 
 					/* iface DUID iaid hostname lifetime assigned length [addrs...] */
-					ctxt.buf_idx = snprintf(ctxt.buf, ctxt.buf_len, "# %s %s ipv4 %s %ld %x 32 ",
+					ctxt.buf_idx = snprintf(ctxt.buf, ctxt.buf_len, "# %s %s ipv4 %s%s %ld %x 32 ",
 								ctxt.iface->ifname, duidbuf,
+								(c->flags & OAF_BROKEN_HOSTNAME) ? "broken\\x20" : "",
 								(c->hostname ? c->hostname : "-"),
 								(c->valid_until > now ?
 									(c->valid_until - now + wall_time) :
@@ -434,7 +437,7 @@ void dhcpv6_write_statefile(void)
 					struct in_addr addr = {.s_addr = c->addr};
 					inet_ntop(AF_INET, &addr, ipbuf, sizeof(ipbuf) - 1);
 
-					if (c->hostname) {
+					if (c->hostname && !(c->flags & OAF_BROKEN_HOSTNAME)) {
 						fputs(ipbuf, ctxt.fp);
 
 						char b[256];
@@ -1343,6 +1346,11 @@ ssize_t dhcpv6_handle_ia(uint8_t *buf, size_t buflen, struct interface *iface,
 					if (a->hostname) {
 						memcpy(a->hostname, hostname, hostname_len);
 						a->hostname[hostname_len] = 0;
+
+						if (odhcpd_valid_hostname(a->hostname))
+							a->flags &= ~OAF_BROKEN_HOSTNAME;
+						else
+							a->flags |= OAF_BROKEN_HOSTNAME;
 					}
 				}
 				a->accept_reconf = accept_reconf;
diff --git a/src/odhcpd.c b/src/odhcpd.c
index fe4dd73..c1d51e7 100644
--- a/src/odhcpd.c
+++ b/src/odhcpd.c
@@ -581,3 +581,38 @@ bool odhcpd_bitlen2netmask(bool inet6, unsigned int bits, void *mask)
 
 	return true;
 }
+
+bool odhcpd_valid_hostname(const char *name)
+{
+#define MAX_LABEL	63
+	const char *c, *label, *label_end;
+	int label_sz = 0;
+
+	for (c = name, label_sz = 0, label = name, label_end = name + strcspn(name, ".") - 1;
+			*c && label_sz <= MAX_LABEL; c++) {
+		if ((*c >= '0' && *c <= '9') ||
+		    (*c >= 'A' && *c <= 'Z') ||
+		    (*c >= 'a' && *c <= 'z')) {
+			label_sz++;
+			continue;
+		}
+
+		if ((*c == '_' || *c == '-') && c != label && c != label_end) {
+			label_sz++;
+			continue;
+		}
+
+		if (*c == '.') {
+			if (*(c + 1)) {
+				label = c + 1;
+				label_end = label + strcspn(label, ".") - 1;
+				label_sz = 0;
+			}
+			continue;
+		}
+
+		return false;
+	}
+
+	return (label_sz && label_sz <= MAX_LABEL ? true : false);
+}
diff --git a/src/odhcpd.h b/src/odhcpd.h
index 91fdcbf..ef94cfc 100644
--- a/src/odhcpd.h
+++ b/src/odhcpd.h
@@ -129,9 +129,10 @@ enum odhcpd_mode {
 
 
 enum odhcpd_assignment_flags {
-	OAF_TENTATIVE	= (1 << 0),
-	OAF_BOUND	= (1 << 1),
-	OAF_STATIC	= (1 << 2),
+	OAF_TENTATIVE		= (1 << 0),
+	OAF_BOUND		= (1 << 1),
+	OAF_STATIC		= (1 << 2),
+	OAF_BROKEN_HOSTNAME	= (1 << 3),
 };
 
 struct config {
@@ -288,6 +289,7 @@ void odhcpd_bmemcpy(void *av, const void *bv, size_t bits);
 
 int odhcpd_netmask2bitlen(bool v6, void *mask);
 bool odhcpd_bitlen2netmask(bool v6, unsigned int bits, void *mask);
+bool odhcpd_valid_hostname(const char *name);
 
 int config_parse_interface(void *data, size_t len, const char *iname, bool overwrite);
 
diff --git a/src/ubus.c b/src/ubus.c
index 5be6bbe..1aec590 100644
--- a/src/ubus.c
+++ b/src/ubus.c
@@ -53,6 +53,9 @@ static int handle_dhcpv4_leases(struct ubus_context *ctx, _unused struct ubus_ob
 
 			if (c->flags & OAF_STATIC)
 				blobmsg_add_string(&b, NULL, "static");
+
+			if (c->flags & OAF_BROKEN_HOSTNAME)
+				blobmsg_add_string(&b, NULL, "broken-hostname");
 			blobmsg_close_array(&b, m);
 
 			buf = blobmsg_alloc_string_buffer(&b, "address", INET_ADDRSTRLEN);