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authorGravatar Denis Vlasenko <vda.linux@googlemail.com>2009-04-12 04:09:09 +0000
committerGravatar Denis Vlasenko <vda.linux@googlemail.com>2009-04-12 04:09:09 +0000
commitddbf3bf35ffd70e7105f4cf8fe8aa81b3c7667e2 (patch)
tree304f23a0e40292b965486ca8564636549d4d2ef2
parent135cecbbcee8bfe10ef7f1edd8e485a7cf86be84 (diff)
downloadbusybox-ddbf3bf35ffd70e7105f4cf8fe8aa81b3c7667e2.tar.gz
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dnsd: fix a number of bugs. Ideas by Ming-Ching Tiew (mctiew AT yahoo.com)
function old new delta undot - 42 +42 dnsd_main 1394 1213 -181 ------------------------------------------------------------------------------ (add/remove: 1/0 grow/shrink: 0/1 up/down: 42/-181) Total: -139 bytes
-rw-r--r--networking/dnsd.c488
1 files changed, 325 insertions, 163 deletions
diff --git a/networking/dnsd.c b/networking/dnsd.c
index f95ba6b40..4f980dccd 100644
--- a/networking/dnsd.c
+++ b/networking/dnsd.c
@@ -24,73 +24,63 @@
#define DEBUG 0
enum {
- MAX_HOST_LEN = 16, // longest host name allowed is 15
- IP_STRING_LEN = 18, // .xxx.xxx.xxx.xxx\0
-
-//must be strlen('.in-addr.arpa') larger than IP_STRING_LEN
- MAX_NAME_LEN = (IP_STRING_LEN + 13),
-
-/* Cannot get bigger packets than 512 per RFC1035
- In practice this can be set considerably smaller:
- Length of response packet is header (12B) + 2*type(4B) + 2*class(4B) +
- ttl(4B) + rlen(2B) + r (MAX_NAME_LEN =21B) +
- 2*querystring (2 MAX_NAME_LEN= 42B), all together 90 Byte
-*/
+ /* Can tweak this */
+ DEFAULT_TTL = 120,
+
+/* Cannot get bigger packets than 512 per RFC1035.
+ * In practice this can be set considerably smaller:
+ * Length of response packet is header (12B) + 2*type(4B) + 2*class(4B) +
+ * ttl(4B) + rlen(2B) + r (MAX_NAME_LEN = 21B) +
+ * 2*querystring (2 MAX_NAME_LEN = 42B), all together 90 Bytes
+ */
MAX_PACK_LEN = 512,
-
- DEFAULT_TTL = 30, // increase this when not testing?
-
+ IP_STRING_LEN = sizeof(".xxx.xxx.xxx.xxx"),
+ MAX_NAME_LEN = IP_STRING_LEN - 1 + sizeof(".in-addr.arpa"),
REQ_A = 1,
- REQ_PTR = 12
+ REQ_PTR = 12,
};
-struct dns_head { // the message from client and first part of response mag
+/* the message from client and first part of response msg */
+struct dns_head {
uint16_t id;
uint16_t flags;
- uint16_t nquer; // accepts 0
- uint16_t nansw; // 1 in response
- uint16_t nauth; // 0
- uint16_t nadd; // 0
+ uint16_t nquer;
+ uint16_t nansw;
+ uint16_t nauth;
+ uint16_t nadd;
};
struct dns_prop {
uint16_t type;
uint16_t class;
};
-struct dns_entry { // element of known name, ip address and reversed ip address
+/* element of known name, ip address and reversed ip address */
+struct dns_entry {
struct dns_entry *next;
- char ip[IP_STRING_LEN]; // dotted decimal IP
- char rip[IP_STRING_LEN]; // length decimal reversed IP
- char name[MAX_HOST_LEN];
+ uint32_t ip;
+ char rip[IP_STRING_LEN]; /* length decimal reversed IP */
+ char name[1];
};
#define OPT_verbose (option_mask32)
/*
- * Convert host name from C-string to dns length/string.
- */
-static void convname(char *a, uint8_t *q)
-{
- int i = (q[0] == '.') ? 0 : 1;
- for (; i < MAX_HOST_LEN-1 && *q; i++, q++)
- a[i] = tolower(*q);
- a[0] = i - 1;
- a[i] = 0;
-}
-
-/*
* Insert length of substrings instead of dots
*/
-static void undot(uint8_t *rip)
+static void undot(char *rip)
{
- int i = 0, s = 0;
+ int i = 0;
+ int s = 0;
+
while (rip[i])
i++;
for (--i; i >= 0; i--) {
if (rip[i] == '.') {
rip[i] = s;
s = 0;
- } else s++;
+ } else {
+ s++;
+ }
}
}
@@ -101,199 +91,369 @@ static struct dns_entry *parse_conf_file(const char *fileconf)
{
char *token[2];
parser_t *parser;
- struct dns_entry *m, *prev, *conf_data;
+ struct dns_entry *m, *conf_data;
+ struct dns_entry **nextp;
+
+ conf_data = NULL;
+ nextp = &conf_data;
- prev = conf_data = NULL;
parser = config_open(fileconf);
while (config_read(parser, token, 2, 2, "# \t", PARSE_NORMAL)) {
- unsigned a, b, c, d;
- /*
- * Assumes all host names are lower case only
- * Hostnames with more than one label are not handled correctly.
- * Presently the dot is copied into name without
- * converting to a length/string substring for that label.
- */
-// if (!token[1] || sscanf(token[1], ".%u.%u.%u.%u"+1, &a, &b, &c, &d) != 4)
- if (sscanf(token[1], ".%u.%u.%u.%u"+1, &a, &b, &c, &d) != 4)
- continue;
+ struct in_addr ip;
+ uint32_t v32;
- m = xzalloc(sizeof(*m));
- /*m->next = NULL;*/
- sprintf(m->ip, ".%u.%u.%u.%u"+1, a, b, c, d);
- sprintf(m->rip, ".%u.%u.%u.%u", d, c, b, a);
- undot((uint8_t*)m->rip);
- convname(m->name, (uint8_t*)token[0]);
+ if (inet_aton(token[1], &ip) == 0) {
+ bb_error_msg("error at line %u, skipping", parser->lineno);
+ continue;
+ }
if (OPT_verbose)
- bb_error_msg("name:%s, ip:%s", &(m->name[1]), m->ip);
+ bb_error_msg("name:%s, ip:%s", token[0], token[1]);
- if (prev == NULL)
- conf_data = m;
- else
- prev->next = m;
- prev = m;
+ /* sizeof(*m) includes 1 byte for m->name[0] */
+ m = xzalloc(sizeof(*m) + strlen(token[0]) + 1);
+ /*m->next = NULL;*/
+ *nextp = m;
+ nextp = &m->next;
+
+ m->name[0] = '.';
+ strcpy(m->name + 1, token[0]);
+ undot(m->name);
+ m->ip = ip.s_addr; /* in network order */
+ v32 = ntohl(m->ip);
+ /* inverted order */
+ sprintf(m->rip, ".%u.%u.%u.%u",
+ (uint8_t)(v32),
+ (uint8_t)(v32 >> 8),
+ (uint8_t)(v32 >> 16),
+ (v32 >> 24)
+ );
+ undot(m->rip);
}
config_close(parser);
return conf_data;
}
/*
- * Look query up in dns records and return answer if found
- * qs is the query string, first byte the string length
+ * Look query up in dns records and return answer if found.
+ * qs is the query string.
*/
-static int table_lookup(struct dns_entry *d, uint16_t type, uint8_t *as, uint8_t *qs)
+static int table_lookup(uint8_t *as, struct dns_entry *d, uint16_t type, uint8_t *qs)
{
- int i;
-
- do {
+ while (d) {
+ unsigned len = d->name[0];
+ /* d->name[len] is the last (non NUL) char */
#if DEBUG
char *p, *q;
q = (char *)&(qs[1]);
p = &(d->name[1]);
- fprintf(stderr, "\n%s: %d/%d p:%s q:%s %d",
- __FUNCTION__, (int)strlen(p), (int)(d->name[0]),
- p, q, (int)strlen(q));
+ fprintf(stderr, "%d/%d p:%s q:%s %d\n",
+ (int)strlen(p), len,
+ p, q, (int)strlen(q)
+ );
#endif
- if (type == REQ_A) {
+ if (type == htons(REQ_A)) {
/* search by host name */
- for (i = 1; i <= (int)(d->name[0]); i++)
- if (tolower(qs[i]) != d->name[i])
- break;
- if (i > (int)(d->name[0])
- || (d->name[0] == 1 && d->name[1] == '*')
- ) {
- strcpy((char *)as, d->ip);
+ if (len != 1 || d->name[1] != '*') {
+ if (strcasecmp(d->name, (char*)qs) != 0)
+ goto next;
+ }
+ move_to_unaligned32((uint32_t *)as, d->ip);
#if DEBUG
- fprintf(stderr, " OK as:%s\n", as);
+ fprintf(stderr, "OK as:%x\n", (int)d->ip);
#endif
- return 0;
- }
- } else if (type == REQ_PTR) {
- /* search by IP-address */
- if ((d->name[0] != 1 || d->name[1] != '*')
- && !strncmp(d->rip + 1, (char*)qs + 1, strlen(d->rip)-1)
- ) {
- strcpy((char *)as, d->name);
- return 0;
- }
+ return 0;
}
+ /* search by IP-address */
+ if ((len != 1 || d->name[1] != '*')
+ /* assume (do not check) that qs ends in ".in-addr.arpa" */
+ && strncmp(d->rip, (char*)qs, strlen(d->rip)) == 0
+ ) {
+ strcpy((char *)as, d->name);
+#if DEBUG
+ fprintf(stderr, "OK as:%s\n", as);
+#endif
+ return 0;
+ }
+ next:
d = d->next;
- } while (d);
+ }
+
return -1;
}
/*
* Decode message and generate answer
*/
+/* RFC 1035
+...
+Whenever an octet represents a numeric quantity, the left most bit
+in the diagram is the high order or most significant bit.
+That is, the bit labeled 0 is the most significant bit.
+...
+
+4.1.1. Header section format
+ 1 1 1 1 1 1
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
+ | ID |
+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
+ |QR| OPCODE |AA|TC|RD|RA| Z | RCODE |
+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
+ | QDCOUNT |
+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
+ | ANCOUNT |
+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
+ | NSCOUNT |
+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
+ | ARCOUNT |
+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
+ID 16 bit random identifier assigned by query.
+ Used to match query/response.
+QR message is a query (0), or a response (1).
+OPCODE 0 standard query (QUERY)
+ 1 inverse query (IQUERY)
+ 2 server status request (STATUS)
+AA Authoritative Answer - this bit is valid in responses,
+ and specifies that the responding name server is an
+ authority for the domain name in question section.
+ Note that the contents of the answer section may have
+ multiple owner names because of aliases. The AA bit
+ corresponds to the name which matches the query name, or
+ the first owner name in the answer section.
+TC TrunCation - specifies that this message was truncated.
+RD Recursion Desired - this bit may be set in a query and
+ is copied into the response. If RD is set, it directs
+ the name server to pursue the query recursively.
+ Recursive query support is optional.
+RA Recursion Available - this be is set or cleared in a
+ response, and denotes whether recursive query support is
+ available in the name server.
+Z Reserved for future use. Must be zero.
+RCODE Response code.
+ 0 No error condition
+ 1 Format error
+ 2 Server failure - The name server was
+ unable to process this query due to a
+ problem with the name server.
+ 3 Name Error - Meaningful only for
+ responses from an authoritative name
+ server, this code signifies that the
+ domain name referenced in the query does
+ not exist.
+ 4 Not Implemented.
+ 5 Refused.
+QDCOUNT number of entries in the question section.
+ANCOUNT number of resource records in the answer section.
+NSCOUNT number of name server resource records in the authority records section.
+ARCOUNT number of resource records in the additional records section.
+
+4.1.2. Question section format
+
+The section contains QDCOUNT (usually 1) entries, each of the following format:
+ 1 1 1 1 1 1
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
+ / QNAME /
+ / /
+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
+ | QTYPE |
+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
+ | QCLASS |
+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
+QNAME a domain name represented as a sequence of labels, where
+ each label consists of a length octet followed by that
+ number of octets. The domain name terminates with the
+ zero length octet for the null label of the root. Note
+ that this field may be an odd number of octets; no
+ padding is used.
+QTYPE a two octet type of the query.
+ 1 a host address [REQ_A const]
+ 2 an authoritative name server
+ 3 a mail destination (Obsolete - use MX)
+ 4 a mail forwarder (Obsolete - use MX)
+ 5 the canonical name for an alias
+ 6 marks the start of a zone of authority
+ 7 a mailbox domain name (EXPERIMENTAL)
+ 8 a mail group member (EXPERIMENTAL)
+ 9 a mail rename domain name (EXPERIMENTAL)
+ 10 a null RR (EXPERIMENTAL)
+ 11 a well known service description
+ 12 a domain name pointer [REQ_PTR const]
+ 13 host information
+ 14 mailbox or mail list information
+ 15 mail exchange
+ 16 text strings
+ 0x1c IPv6?
+ 252 a request for a transfer of an entire zone
+ 253 a request for mailbox-related records (MB, MG or MR)
+ 254 a request for mail agent RRs (Obsolete - see MX)
+ 255 a request for all records
+QCLASS a two octet code that specifies the class of the query.
+ 1 the Internet
+ (others are historic only)
+ 255 any class
+
+4.1.3. Resource record format
+
+The answer, authority, and additional sections all share the same
+format: a variable number of resource records, where the number of
+records is specified in the corresponding count field in the header.
+Each resource record has the following format:
+ 1 1 1 1 1 1
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
+ / /
+ / NAME /
+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
+ | TYPE |
+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
+ | CLASS |
+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
+ | TTL |
+ | |
+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
+ | RDLENGTH |
+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--|
+ / RDATA /
+ / /
+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
+NAME a domain name to which this resource record pertains.
+TYPE two octets containing one of the RR type codes. This
+ field specifies the meaning of the data in the RDATA
+ field.
+CLASS two octets which specify the class of the data in the
+ RDATA field.
+TTL a 32 bit unsigned integer that specifies the time
+ interval (in seconds) that the resource record may be
+ cached before it should be discarded. Zero values are
+ interpreted to mean that the RR can only be used for the
+ transaction in progress, and should not be cached.
+RDLENGTH an unsigned 16 bit integer that specifies the length in
+ octets of the RDATA field.
+RDATA a variable length string of octets that describes the
+ resource. The format of this information varies
+ according to the TYPE and CLASS of the resource record.
+ For example, if the TYPE is A and the CLASS is IN,
+ the RDATA field is a 4 octet ARPA Internet address.
+
+4.1.4. Message compression
+
+In order to reduce the size of messages, the domain system utilizes a
+compression scheme which eliminates the repetition of domain names in a
+message. In this scheme, an entire domain name or a list of labels at
+the end of a domain name is replaced with a pointer to a prior occurance
+of the same name.
+
+The pointer takes the form of a two octet sequence:
+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
+ | 1 1| OFFSET |
+ +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
+The first two bits are ones. This allows a pointer to be distinguished
+from a label, since the label must begin with two zero bits because
+labels are restricted to 63 octets or less. The OFFSET field specifies
+an offset from the start of the message (i.e., the first octet
+of the ID field in the domain header).
+A zero offset specifies the first byte of the ID field, etc.
+
+The compression scheme allows a domain name in a message to be
+represented as either:
+ - a sequence of labels ending in a zero octet
+ - a pointer
+ - a sequence of labels ending with a pointer
+ */
static int process_packet(struct dns_entry *conf_data, uint32_t conf_ttl, uint8_t *buf)
{
uint8_t answstr[MAX_NAME_LEN + 1];
struct dns_head *head;
- struct dns_prop *qprop;
+ struct dns_prop *unaligned_qprop;
uint8_t *from, *answb;
uint16_t outr_rlen;
uint16_t outr_flags;
- uint16_t flags;
- int lookup_result, type, packet_len;
+ uint16_t type;
+ uint16_t class;
int querystr_len;
answstr[0] = '\0';
head = (struct dns_head *)buf;
if (head->nquer == 0) {
- bb_error_msg("no queries");
+ bb_error_msg("packet has 0 queries, ignored");
return -1;
}
- if (head->flags & 0x8000) {
- bb_error_msg("ignoring response packet");
+ if (head->flags & htons(0x8000)) { /* QR bit */
+ bb_error_msg("response packet, ignored");
return -1;
}
- from = (void *)&head[1]; // start of query string
-//FIXME: strlen of untrusted data??!
- querystr_len = strlen((char *)from) + 1 + sizeof(struct dns_prop);
- answb = from + querystr_len; // where to append answer block
+ /* start of query string */
+ from = (void *)(head + 1);
+ /* caller guarantees strlen is <= MAX_PACK_LEN */
+ querystr_len = strlen((char *)from) + 1;
+ /* may be unaligned! */
+ unaligned_qprop = (void *)(from + querystr_len);
+ /* where to append answer block */
+ answb = (void *)(unaligned_qprop + 1);
outr_rlen = 0;
- outr_flags = 0;
-
- qprop = (struct dns_prop *)(answb - 4);
- type = ntohs(qprop->type);
+ /* QR = 1 "response", RCODE = 4 "Not Implemented" */
+ outr_flags = htons(0x8000 | 4);
- // only let REQ_A and REQ_PTR pass
- if (!(type == REQ_A || type == REQ_PTR)) {
- goto empty_packet; /* we can't handle the query type */
+ move_from_unaligned16(type, &unaligned_qprop->type);
+ if (type != htons(REQ_A) && type != htons(REQ_PTR)) {
+ /* we can't handle the query type */
+ goto empty_packet;
}
-
- if (ntohs(qprop->class) != 1 /* class INET */ ) {
- outr_flags = 4; /* not supported */
+ move_from_unaligned16(class, &unaligned_qprop->class);
+ if (class != htons(1)) { /* not class INET? */
goto empty_packet;
}
- /* we only support standard queries */
-
- if ((ntohs(head->flags) & 0x7800) != 0)
+ /* OPCODE != 0 "standard query" ? */
+ if ((head->flags & htons(0x7800)) != 0) {
goto empty_packet;
+ }
- // We have a standard query
bb_info_msg("%s", (char *)from);
- lookup_result = table_lookup(conf_data, type, answstr, from);
- if (lookup_result != 0) {
- outr_flags = 3 | 0x0400; // name do not exist and auth
+ if (table_lookup(answstr, conf_data, type, from) != 0) {
+ /* QR = 1 "response"
+ * AA = 1 "Authoritative Answer"
+ * RCODE = 3 "Name Error" */
+ outr_flags = htons(0x8000 | 0x0400 | 3);
goto empty_packet;
}
- if (type == REQ_A) { // return an address
- struct in_addr a; // NB! its "struct { unsigned __long__ s_addr; }"
- uint32_t v32;
- if (!inet_aton((char*)answstr, &a)) { //dotted dec to long conv
- outr_flags = 1; /* Frmt err */
- goto empty_packet;
- }
- v32 = a.s_addr; /* in case long != int */
- move_to_unaligned32(answstr, v32);
- outr_rlen = 4; // uint32_t IP
- } else
- outr_rlen = strlen((char *)answstr) + 1; // a host name
- outr_flags |= 0x0400; /* authority-bit */
- // we have an answer
+ /* return an address */
+ outr_rlen = 4;
+ if (type == htons(REQ_PTR)) {
+ /* return a host name */
+ outr_rlen = strlen((char *)answstr) + 1;
+ }
+ /* QR = 1 "response",
+ * AA = 1 "Authoritative Answer",
+ * RCODE = 0 "success" */
+ outr_flags = htons(0x8000 | 0x0400 | 0);
+ /* we have one answer */
head->nansw = htons(1);
-
- // copy query block to answer block
+ /* copy query block to answer block */
+ querystr_len += sizeof(unaligned_qprop);
memcpy(answb, from, querystr_len);
answb += querystr_len;
-
- // and append answer rr
-// FIXME: unaligned accesses??
- *(uint32_t *) answb = htonl(conf_ttl);
+ /* append answer Resource Record */
+ move_to_unaligned32((uint32_t *)answb, htonl(conf_ttl));
answb += 4;
- *(uint16_t *) answb = htons(outr_rlen);
+ move_to_unaligned32((uint16_t *)answb, htons(outr_rlen));
answb += 2;
memcpy(answb, answstr, outr_rlen);
answb += outr_rlen;
empty_packet:
-
- flags = ntohs(head->flags);
- // clear rcode and RA, set responsebit and our new flags
- flags |= (outr_flags & 0xff80) | 0x8000;
- head->flags = htons(flags);
+ head->flags |= outr_flags;
head->nauth = head->nadd = 0;
- head->nquer = htons(1);
+ head->nquer = htons(1); // why???
- packet_len = answb - buf;
- return packet_len;
+ return answb - buf;
}
-/*
- * Exit on signal
- */
-//static void interrupt(int sig)
-//{
-// /* unlink("/var/run/dnsd.lock"); */
-// bb_error_msg("interrupt, exiting\n");
-// kill_myself_with_sig(sig);
-//}
-
int dnsd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int dnsd_main(int argc UNUSED_PARAM, char **argv)
{
@@ -328,7 +488,6 @@ int dnsd_main(int argc UNUSED_PARAM, char **argv)
conf_data = parse_conf_file(fileconf);
-// signal(SIGINT, interrupt); - just for one message?
bb_signals(0
/* why? + (1 << SIGPIPE) */
+ (1 << SIGHUP)
@@ -348,8 +507,11 @@ int dnsd_main(int argc UNUSED_PARAM, char **argv)
from = xzalloc(lsa_size);
to = xzalloc(lsa_size);
- bb_info_msg("Accepting UDP packets on %s",
- xmalloc_sockaddr2dotted(&lsa->u.sa));
+ {
+ char *p = xmalloc_sockaddr2dotted(&lsa->u.sa);
+ bb_info_msg("Accepting UDP packets on %s", p);
+ free(p);
+ }
while (1) {
int r;
@@ -361,7 +523,7 @@ int dnsd_main(int argc UNUSED_PARAM, char **argv)
memcpy(to, lsa, lsa_size);
r = recv_from_to(udps, buf, MAX_PACK_LEN + 1, 0, &from->u.sa, &to->u.sa, lsa->len);
if (r < 12 || r > MAX_PACK_LEN) {
- bb_error_msg("invalid packet size");
+ bb_error_msg("packet size %d, ignored", r);
continue;
}
if (OPT_verbose)