/*
* Look query up in dns records and return answer if found.
- * qs is the query string.
*/
-static int table_lookup(uint8_t *as, struct dns_entry *d, uint16_t type, uint8_t *qs)
+static char *table_lookup(struct dns_entry *d,
+ uint16_t type,
+ char* query_string)
{
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]);
+ q = query_string + 1;
+ p = d->name + 1;
fprintf(stderr, "%d/%d p:%s q:%s %d\n",
(int)strlen(p), len,
p, q, (int)strlen(q)
if (type == htons(REQ_A)) {
/* search by host name */
if (len != 1 || d->name[1] != '*') {
- if (strcasecmp(d->name, (char*)qs) != 0)
+/* we are lax, hope no name component is ever >64 so that length
+ * (which will be represented as 'A','B'...) matches a lowercase letter.
+ * Actually, I think false matches are hard to construct.
+ * Example.
+ * [31] len is represented as '1', [65] as 'A', [65+32] as 'a'.
+ * [65] <65 same chars>[31]<31 same chars>NUL
+ * [65+32]<65 same chars>1 <31 same chars>NUL
+ * This example seems to be the minimal case when false match occurs.
+ */
+ if (strcasecmp(d->name, query_string) != 0)
goto next;
}
- move_to_unaligned32((uint32_t *)as, d->ip);
+ return (char *)&d->ip;
#if DEBUG
- fprintf(stderr, "OK as:%x\n", (int)d->ip);
+ fprintf(stderr, "Found IP:%x\n", (int)d->ip);
#endif
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
+ /* we assume (do not check) that query_string
+ * ends in ".in-addr.arpa" */
+ && strncmp(d->rip, query_string, strlen(d->rip)) == 0
) {
- strcpy((char *)as, d->name);
#if DEBUG
- fprintf(stderr, "OK as:%s\n", as);
+ fprintf(stderr, "Found name:%s\n", d->name);
#endif
- return 0;
+ return d->name;
}
next:
d = d->next;
}
- return -1;
+ return NULL;
}
/*
...
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
+ 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
- |QR| OPCODE |AA|TC|RD|RA| Z | RCODE |
+ |QR| OPCODE |AA|TC|RD|RA| 0 0 0| RCODE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| QDCOUNT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| ARCOUNT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
-ID 16 bit random identifier assigned by query.
+ID 16 bit random identifier assigned by querying peer.
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.
+AA Authoritative Answer - this bit is valid in responses.
+ Responding name server is an authority for the domain name
+ in question section. 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 - 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.
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.
+ 2 Server failure - server was unable to process the query
+ due to a problem with the name server.
+ 3 Name Error - meaningful only for responses from
+ an authoritative name server. The referenced domain name
+ 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.
+ANCOUNT number of records in the answer section.
+NSCOUNT number of records in the authority records section.
+ARCOUNT number of 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
+The section contains QDCOUNT (usually 1) entries, each of this format:
+ 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
/ QNAME /
/ /
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
+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 this format:
+ 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
/ /
/ NAME /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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.
+ 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 record may be cached.
+RDLENGTH a 16 bit integer, 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.
+ If the TYPE is A and the CLASS is IN, it's a 4 octet IP 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.
+In order to reduce the size of messages, domain names coan be compressed.
+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:
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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:
+Domain name in a message can 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)
+static int process_packet(struct dns_entry *conf_data,
+ uint32_t conf_ttl,
+ uint8_t *buf)
{
- uint8_t answstr[MAX_NAME_LEN + 1];
+ char *answstr;
struct dns_head *head;
struct dns_prop *unaligned_qprop;
- uint8_t *from, *answb;
+ char *query_string;
+ uint8_t *answb;
uint16_t outr_rlen;
uint16_t outr_flags;
uint16_t type;
uint16_t class;
int querystr_len;
- answstr[0] = '\0';
-
head = (struct dns_head *)buf;
if (head->nquer == 0) {
bb_error_msg("packet has 0 queries, ignored");
}
/* start of query string */
- from = (void *)(head + 1);
+ query_string = (void *)(head + 1);
/* caller guarantees strlen is <= MAX_PACK_LEN */
- querystr_len = strlen((char *)from) + 1;
+ querystr_len = strlen(query_string) + 1;
/* may be unaligned! */
- unaligned_qprop = (void *)(from + querystr_len);
+ unaligned_qprop = (void *)(query_string + querystr_len);
+ querystr_len += sizeof(unaligned_qprop);
/* where to append answer block */
answb = (void *)(unaligned_qprop + 1);
- outr_rlen = 0;
/* QR = 1 "response", RCODE = 4 "Not Implemented" */
outr_flags = htons(0x8000 | 4);
goto empty_packet;
}
- bb_info_msg("%s", (char *)from);
- if (table_lookup(answstr, conf_data, type, from) != 0) {
+ /* look up the name */
+#if DEBUG
+ /* need to convert lengths to dots before we can use it in non-debug */
+ bb_info_msg("%s", query_string);
+#endif
+ answstr = table_lookup(conf_data, type, query_string);
+ outr_rlen = 4;
+ if (answstr && type == htons(REQ_PTR)) {
+ /* return a host name */
+ outr_rlen = strlen(answstr) + 1;
+ }
+ if (!answstr
+ || (unsigned)(answb - buf) + querystr_len + 4 + 2 + outr_rlen > MAX_PACK_LEN
+ ) {
/* QR = 1 "response"
* AA = 1 "Authoritative Answer"
* RCODE = 3 "Name Error" */
outr_flags = htons(0x8000 | 0x0400 | 3);
goto empty_packet;
}
- /* 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 */
- querystr_len += sizeof(unaligned_qprop);
- memcpy(answb, from, querystr_len);
+ memcpy(answb, query_string, querystr_len);
answb += querystr_len;
/* append answer Resource Record */
move_to_unaligned32((uint32_t *)answb, htonl(conf_ttl));
memcpy(answb, answstr, outr_rlen);
answb += outr_rlen;
+ /* QR = 1 "response",
+ * AA = 1 "Authoritative Answer",
+ * RCODE = 0 "success" */
+ outr_flags = htons(0x8000 | 0x0400 | 0);
+ /* we have one answer */
+ head->nansw = htons(1);
+
empty_packet:
head->flags |= outr_flags;
head->nauth = head->nadd = 0;
projects / oweals / busybox.git / commitdiff