[Call for reviews] Support domain-search option in dhclient(8)
Jean-Sébastien Pédron
dumbbell at FreeBSD.org
Sat Nov 12 16:07:07 UTC 2011
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Hi!
Attached is a patch that adds support for "domain-search" option
(#119) as defined in RFC 3397[1]. This allows a DHCP server to publish
a list of domain names that should be used to search for non-fully
qualified domain names.
There's already a PR opened about this:
http://www.freebsd.org/cgi/query-pr.cgi?pr=151940
With this patch applied and a DHCP server configured to publish this
option, dhclient(8) will add a line similar to the following one:
search example.org. foobar.com.
In the example, this indicates that the name "www" should be resolved
first as "www.example.org", then as "www.foobar.com".
I prepared a regression test to be added to tools/regression (not
included). However, I'm not knowledgeable enough to anticipate all
security-related issues. I would appreciate a review especially with
this in mind :)
Thank you!
[1] http://www.faqs.org/rfcs/rfc3397.html
- --
Jean-Sébastien Pédron
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Index: sbin/dhclient/dhcp.h
===================================================================
--- sbin/dhclient/dhcp.h (revision 227467)
+++ sbin/dhclient/dhcp.h (working copy)
@@ -169,6 +169,7 @@
#define DHO_STREETTALK_SERVER 75
#define DHO_STREETTALK_DA_SERVER 76
#define DHO_DHCP_USER_CLASS_ID 77
+#define DHO_DOMAIN_SEARCH 119
#define DHO_CLASSLESS_ROUTES 121
#define DHO_END 255
Index: sbin/dhclient/dhclient.c
===================================================================
--- sbin/dhclient/dhclient.c (revision 227467)
+++ sbin/dhclient/dhclient.c (working copy)
@@ -2453,6 +2453,7 @@
case DHO_DHCP_CLIENT_IDENTIFIER:
case DHO_BOOTFILE_NAME:
case DHO_DHCP_USER_CLASS_ID:
+ case DHO_DOMAIN_SEARCH:
case DHO_END:
return (1);
case DHO_CLASSLESS_ROUTES:
Index: sbin/dhclient/tables.c
===================================================================
--- sbin/dhclient/tables.c (revision 227467)
+++ sbin/dhclient/tables.c (working copy)
@@ -184,7 +184,7 @@
{ "option-116", "X", &dhcp_universe, 116 },
{ "option-117", "X", &dhcp_universe, 117 },
{ "option-118", "X", &dhcp_universe, 118 },
- { "option-119", "X", &dhcp_universe, 119 },
+ { "domain-search", "t", &dhcp_universe, 119 },
{ "option-120", "X", &dhcp_universe, 120 },
{ "classless-routes", "BA", &dhcp_universe, 121 },
{ "option-122", "X", &dhcp_universe, 122 },
@@ -400,12 +400,13 @@
DHO_IRC_SERVER,
DHO_STREETTALK_SERVER,
DHO_STREETTALK_DA_SERVER,
+ DHO_DOMAIN_SEARCH,
/* Presently-undefined options... */
62, 63, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91,
92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105,
106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117,
- 118, 119, 120, 122, 123, 124, 125, 126, 127, 128, 129, 130,
+ 118, 120, 122, 123, 124, 125, 126, 127, 128, 129, 130,
131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142,
143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154,
155, 156, 157, 158, 159, 160, 161, 162, 163, 164, 165, 166,
Index: sbin/dhclient/clparse.c
===================================================================
--- sbin/dhclient/clparse.c (revision 227467)
+++ sbin/dhclient/clparse.c (working copy)
@@ -100,6 +100,8 @@
DHO_DOMAIN_NAME_SERVERS;
top_level_config.requested_options
[top_level_config.requested_option_count++] = DHO_HOST_NAME;
+ top_level_config.requested_options
+ [top_level_config.requested_option_count++] = DHO_DOMAIN_SEARCH;
if ((cfile = fopen(path_dhclient_conf, "r")) != NULL) {
do {
Index: sbin/dhclient/options.c
===================================================================
--- sbin/dhclient/options.c (revision 227467)
+++ sbin/dhclient/options.c (working copy)
@@ -55,6 +55,10 @@
void parse_option_buffer(struct packet *, unsigned char *, int);
int store_options(unsigned char *, int, struct tree_cache **,
unsigned char *, int, int, int, int);
+void expand_domain_search(struct packet *packet);
+int find_search_domain_name_len(struct option_data *option, int *offset);
+void expand_search_domain_name(struct option_data *option, int *offset,
+ unsigned char **domain_search);
/*
@@ -94,6 +98,11 @@
(unsigned char *)packet->raw->sname,
sizeof(packet->raw->sname));
}
+
+ /* Expand DHCP Domain Search option. */
+ if (packet->options_valid) {
+ expand_domain_search(packet);
+ }
}
/*
@@ -194,6 +203,163 @@
}
/*
+ * Expand DHCP Domain Search option. The value of this option is
+ * encoded like DNS' list of labels. See:
+ * RFC 3397
+ * RFC 1035
+ */
+void
+expand_domain_search(struct packet *packet)
+{
+ int offset, expanded_len;
+ struct option_data *option;
+ unsigned char *domain_search, *cursor;
+
+ if (packet->options[DHO_DOMAIN_SEARCH].data == NULL)
+ return;
+
+ option = &packet->options[DHO_DOMAIN_SEARCH];
+
+ /* Compute final expanded length. */
+ expanded_len = 0;
+ offset = 0;
+ while (offset < option->len) {
+ /* We add 1 for the space between domain names. */
+ expanded_len +=
+ find_search_domain_name_len(option, &offset) + 1;
+ }
+ if (expanded_len > 0)
+ /* Remove 1 for the superfluous trailing space. */
+ --expanded_len;
+
+ domain_search = malloc(expanded_len + 1);
+ if (domain_search == NULL)
+ error("Can't allocate storage for expanded domain-search\n");
+
+ offset = 0;
+ cursor = domain_search;
+ while (offset < option->len) {
+ expand_search_domain_name(option, &offset, &cursor);
+ cursor[0] = ' ';
+ cursor++;
+ }
+ domain_search[expanded_len] = '\0';
+
+ free(option->data);
+ option->len = expanded_len;
+ option->data = domain_search;
+}
+
+int
+find_search_domain_name_len(struct option_data *option, int *offset)
+{
+ int domain_name_len, i, label_len, pointer, pointed_len;
+
+ domain_name_len = 0;
+
+ i = *offset;
+ while (i < option->len) {
+ label_len = option->data[i];
+ if (label_len == 0) {
+ /*
+ * A zero-length label marks the end of this
+ * domain name.
+ */
+ *offset = i + 1;
+ return (domain_name_len);
+ } else if (label_len & 0xC0) {
+ /* This is a pointer to another list of labels. */
+ if (i + 1 >= option->len) {
+ /* The pointer is truncated. */
+ error("Truncated pointer in DHCP Domain "
+ "Search option.");
+ }
+
+ pointer = ((label_len & ~(0xC0)) << 8) +
+ option->data[i + 1];
+ if (pointer >= *offset) {
+ /*
+ * The pointer must indicates a prior
+ * occurance.
+ */
+ error("Invalid forward pointer in DHCP Domain "
+ "Search option compression.");
+ }
+
+ pointed_len = find_search_domain_name_len(option,
+ &pointer);
+ domain_name_len += pointed_len;
+
+ *offset = i + 2;
+ return (domain_name_len);
+ }
+
+ if (i + label_len >= option->len) {
+ error("Truncated label in DHCP Domain Search option.");
+ }
+
+ /*
+ * Update the domain name length with the length of the
+ * current label, plus a trailing dot ('.').
+ */
+ domain_name_len += label_len + 1;
+
+ /* Move cursor. */
+ i += label_len + 1;
+ }
+
+ error("Truncated DHCP Domain Search option.");
+
+ return (0);
+}
+
+void
+expand_search_domain_name(struct option_data *option, int *offset,
+ unsigned char **domain_search)
+{
+ int i, label_len, pointer;
+ unsigned char *cursor;
+
+ /*
+ * This is the same loop than the function above
+ * (find_search_domain_name_len). Therefore, we remove checks,
+ * they're already done. Here, we just make the copy.
+ */
+ i = *offset;
+ cursor = *domain_search;
+ while (i < option->len) {
+ label_len = option->data[i];
+ if (label_len == 0) {
+ /*
+ * A zero-length label marks the end of this
+ * domain name.
+ */
+ *offset = i + 1;
+ *domain_search = cursor;
+ return;
+ } else if (label_len & 0xC0) {
+ /* This is a pointer to another list of labels. */
+ pointer = ((label_len & ~(0xC0)) << 8) +
+ option->data[i + 1];
+
+ expand_search_domain_name(option, &pointer, &cursor);
+
+ *offset = i + 2;
+ *domain_search = cursor;
+ return;
+ }
+
+ /* Copy the label found. */
+ memcpy(cursor, option->data + i + 1, label_len);
+ cursor[label_len] = '.';
+
+ /* Move cursor. */
+ i += label_len + 1;
+ cursor += label_len + 1;
+ }
+}
+
+/*
* cons options into a big buffer, and then split them out into the
* three separate buffers if needed. This allows us to cons up a set of
* vendor options using the same routine.
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