DNS protocol. More...

#include <stdint.h>
#include <ipxe/in.h>

Data Structures
struct	dns_name
	An RFC1035-encoded DNS name. More...

struct	dns_header
	A DNS packet header. More...

struct	dns_question
	A DNS question. More...

struct	dns_rr_common
	A DNS resource record. More...

struct	dns_rr_a
	A DNS "A" record. More...

struct	dns_rr_aaaa
	A DNS "AAAA" record. More...

struct	dns_rr_cname
	A DNS "CNAME" record. More...

union	dns_rr
	A DNS resource record. More...

Macros
#define	DNS_PORT 53
	DNS server port. More...

#define	DNS_IS_COMPRESSED(byte) ( (byte) & 0xc0 )
	Test for a DNS compression pointer. More...

#define	DNS_COMPRESSED_OFFSET(word) ( (word) & ~0xc000 )
	Extract DNS compression pointer. More...

#define	DNS_LABEL_LEN(byte) ( (byte) & ~0xc0 )
	Extract DNS label length. More...

#define	DNS_MAX_LABEL_LEN 0x3f
	Maximum length of a single DNS label. More...

#define	DNS_MAX_NAME_LEN 255
	Maximum length of a DNS name (mandated by RFC1035 section 2.3.4) More...

#define	DNS_MAX_CNAME_RECURSION 32
	Maximum depth of CNAME recursion. More...

#define	DNS_FLAG_RD 0x0100
	Recursion desired flag. More...

#define	DNS_CLASS_IN 1
	DNS class "IN". More...

#define	DNS_TYPE_A 1
	Type of a DNS "A" record. More...

#define	DNS_TYPE_AAAA 28
	Type of a DNS "AAAA" record. More...

#define	DNS_TYPE_CNAME 5
	Type of a DNS "NAME" record. More...

Functions
	FILE_LICENCE (GPL2_OR_LATER_OR_UBDL)

int	dns_encode (const char string, struct dns_name name)
	Encode a DNS name using RFC1035 encoding. More...

int	dns_decode (struct dns_name name, char data, size_t len)
	Decode RFC1035-encoded DNS name. More...

int	dns_compare (struct dns_name first, struct dns_name second)
	Compare DNS names for equality. More...

int	dns_copy (struct dns_name src, struct dns_name dst)
	Copy a DNS name. More...

int	dns_skip (struct dns_name *name)
	Skip RFC1035-encoded DNS name. More...

Detailed Description

DNS protocol.

Definition in file dns.h.

Macro Definition Documentation

◆ DNS_PORT

#define DNS_PORT 53

DNS server port.

Definition at line 16 of file dns.h.

◆ DNS_IS_COMPRESSED

#define DNS_IS_COMPRESSED ( byte ) ( (byte) & 0xc0 )

Test for a DNS compression pointer.

Parameters

byte	Initial byte

Return values

is_compressed Is a compression pointer

Definition at line 34 of file dns.h.

◆ DNS_COMPRESSED_OFFSET

#define DNS_COMPRESSED_OFFSET ( word ) ( (word) & ~0xc000 )

Extract DNS compression pointer.

Parameters

word	Initial word

Return values

offset Offset

Definition at line 42 of file dns.h.

◆ DNS_LABEL_LEN

#define DNS_LABEL_LEN ( byte ) ( (byte) & ~0xc0 )

Extract DNS label length.

Parameters

byte	Initial byte

Return values

len	Label length

Definition at line 50 of file dns.h.

◆ DNS_MAX_LABEL_LEN

#define DNS_MAX_LABEL_LEN 0x3f

Maximum length of a single DNS label.

Definition at line 53 of file dns.h.

◆ DNS_MAX_NAME_LEN

#define DNS_MAX_NAME_LEN 255

Maximum length of a DNS name (mandated by RFC1035 section 2.3.4)

Definition at line 56 of file dns.h.

◆ DNS_MAX_CNAME_RECURSION

#define DNS_MAX_CNAME_RECURSION 32

Maximum depth of CNAME recursion.

This is a policy decision.

Definition at line 62 of file dns.h.

◆ DNS_FLAG_RD

#define DNS_FLAG_RD 0x0100

Recursion desired flag.

Definition at line 81 of file dns.h.

◆ DNS_CLASS_IN

#define DNS_CLASS_IN 1

DNS class "IN".

Definition at line 92 of file dns.h.

◆ DNS_TYPE_A

#define DNS_TYPE_A 1

Type of a DNS "A" record.

Definition at line 107 of file dns.h.

◆ DNS_TYPE_AAAA

#define DNS_TYPE_AAAA 28

Type of a DNS "AAAA" record.

Definition at line 118 of file dns.h.

◆ DNS_TYPE_CNAME

#define DNS_TYPE_CNAME 5

Type of a DNS "NAME" record.

Definition at line 129 of file dns.h.

Function Documentation

◆ FILE_LICENCE()

FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL )

◆ dns_encode()

int dns_encode	(	const char *	string,
		struct dns_name *	name
	)

Encode a DNS name using RFC1035 encoding.

Parameters

string	DNS name as a string
name	DNS name to fill in

Return values

len	Length of DNS name, or negative error

Definition at line 100 of file dns.c.

                                                              {
         uint8_t *start = ( name->data + name->offset );
         uint8_t *end = ( name->data + name->len );
         uint8_t *dst = start;
         size_t len = 0;
         char c;
 
         /* Encode name */
         while ( ( c = *(string++) ) ) {
 
                 /* Handle '.' separators */
                 if ( c == '.' ) {
 
                         /* Reject consecutive '.' */
                         if ( ( len == 0 ) && ( dst != start ) )
                                 return -EINVAL;
 
                         /* Terminate if this is the trailing '.' */
                         if ( *string == '\0' )
                                 break;
 
                         /* Reject initial non-terminating '.' */
                         if ( len == 0 )
                                 return -EINVAL;
 
                         /* Reset length */
                         len = 0;
 
                 } else {
 
                         /* Increment length */
                         len++;
 
                         /* Check for overflow */
                         if ( len > DNS_MAX_LABEL_LEN )
                                 return -EINVAL;
                 }
 
                 /* Copy byte, update length */
                 if ( ++dst < end ) {
                         *dst = c;
                         dst[-len] = len;
                 }
         }
 
         /* Add terminating root marker */
         if ( len )
                 dst++;
         if ( dst < end )
                 *dst = '\0';
         dst++;
 
         return ( dst - start );
 }

References c, DNS_MAX_LABEL_LEN, EINVAL, end, len, name, and start.

Referenced by apply_dns_search(), dns_encode_fail_okx(), dns_encode_okx(), and dns_resolv().

◆ dns_decode()

int dns_decode	(	struct dns_name *	name,
		char *	data,
		size_t	len
	)

Decode RFC1035-encoded DNS name.

Parameters

name	DNS name
data	Output buffer
len	Length of output buffer

Return values

len	Length of decoded DNS name, or negative error

Definition at line 216 of file dns.c.

                                                                  {
         unsigned int recursion_limit = name->len; /* Generous upper bound */
         int offset = name->offset;
         const uint8_t *label;
         size_t decoded_len = 0;
         size_t label_len;
         size_t copy_len;
 
         while ( recursion_limit-- ) {
 
                 /* Find valid DNS label */
                 offset = dns_label ( name, offset );
                 if ( offset < 0 )
                         return offset;
 
                 /* Terminate if we have reached the root */
                 label = ( name->data + offset );
                 label_len = *(label++);
                 if ( label_len == 0 ) {
                         if ( decoded_len < len )
                                 *data = '\0';
                         return decoded_len;
                 }
 
                 /* Prepend '.' if applicable */
                 if ( decoded_len && ( decoded_len++ < len ) )
                         *(data++) = '.';
 
                 /* Copy label to output buffer */
                 copy_len = ( ( decoded_len < len ) ? ( len - decoded_len ) : 0);
                 if ( copy_len > label_len )
                         copy_len = label_len;
                 memcpy ( data, label, copy_len );
                 data += copy_len;
                 decoded_len += label_len;
 
                 /* Move to next label */
                 offset += ( sizeof ( *label ) + label_len );
         }
 
         /* Recursion limit exceeded */
         return -EINVAL;
 }

References data, dns_label(), EINVAL, len, memcpy(), name, and offset.

Referenced by dns_decode_fail_okx(), dns_decode_okx(), dns_list_okx(), dns_name(), dns_progress(), and format_dnssl_setting().

◆ dns_compare()

int dns_compare	(	struct dns_name *	first,
		struct dns_name *	second
	)

Compare DNS names for equality.

Parameters

first	First DNS name
second	Second DNS name

Return values

rc	Return status code

Definition at line 267 of file dns.c.

                                                                     {
         unsigned int recursion_limit = first->len; /* Generous upper bound */
         int first_offset = first->offset;
         int second_offset = second->offset;
         const uint8_t *first_label;
         const uint8_t *second_label;
         size_t label_len;
         size_t len;
 
         while ( recursion_limit-- ) {
 
                 /* Find valid DNS labels */
                 first_offset = dns_label ( first, first_offset );
                 if ( first_offset < 0 )
                         return first_offset;
                 second_offset = dns_label ( second, second_offset );
                 if ( second_offset < 0 )
                         return second_offset;
 
                 /* Compare label lengths */
                 first_label = ( first->data + first_offset );
                 second_label = ( second->data + second_offset );
                 label_len = *(first_label++);
                 if ( label_len != *(second_label++) )
                         return -ENOENT;
                 len = ( sizeof ( *first_label ) + label_len );
 
                 /* Terminate if we have reached the root */
                 if ( label_len == 0 )
                         return 0;
 
                 /* Compare label contents (case-insensitively) */
                 while ( label_len-- ) {
                         if ( tolower ( *(first_label++) ) !=
                              tolower ( *(second_label++) ) )
                                 return -ENOENT;
                 }
 
                 /* Move to next labels */
                 first_offset += len;
                 second_offset += len;
         }
 
         /* Recursion limit exceeded */
         return -EINVAL;
 }

References dns_label(), EINVAL, ENOENT, first, len, second, and tolower().

Referenced by dns_compare_fail_okx(), dns_compare_okx(), and dns_xfer_deliver().

◆ dns_copy()

int dns_copy	(	struct dns_name *	src,
		struct dns_name *	dst
	)

Copy a DNS name.

Parameters

src	Source DNS name
dst	Destination DNS name

Return values

len	Length of copied DNS name, or negative error

Definition at line 321 of file dns.c.

                                                             {
         unsigned int recursion_limit = src->len; /* Generous upper bound */
         int src_offset = src->offset;
         size_t dst_offset = dst->offset;
         const uint8_t *label;
         size_t label_len;
         size_t copy_len;
         size_t len;
 
         while ( recursion_limit-- ) {
 
                 /* Find valid DNS label */
                 src_offset = dns_label ( src, src_offset );
                 if ( src_offset < 0 )
                         return src_offset;
 
                 /* Copy as an uncompressed label */
                 label = ( src->data + src_offset );
                 label_len = *label;
                 len = ( sizeof ( *label ) + label_len );
                 copy_len = ( ( dst_offset < dst->len ) ?
                              ( dst->len - dst_offset ) : 0 );
                 if ( copy_len > len )
                         copy_len = len;
                 memcpy ( ( dst->data + dst_offset ), label, copy_len );
                 src_offset += len;
                 dst_offset += len;
 
                 /* Terminate if we have reached the root */
                 if ( label_len == 0 )
                         return ( dst_offset - dst->offset );
         }
 
         /* Recursion limit exceeded */
         return -EINVAL;
 }

References dns_name::data, dns_label(), EINVAL, len, dns_name::len, memcpy(), dns_name::offset, and src.

Referenced by dns_copy_fail_okx(), dns_copy_okx(), dns_question(), and dns_xfer_deliver().

◆ dns_skip()

int dns_skip ( struct dns_name * name )

Skip RFC1035-encoded DNS name.

Parameters

name DNS name

Return values

offset Offset to next name, or negative error

Definition at line 364 of file dns.c.

                                        {
         unsigned int recursion_limit = name->len; /* Generous upper bound */
         int offset = name->offset;
         int prev_offset;
         const uint8_t *label;
         size_t label_len;
 
         while ( recursion_limit-- ) {
 
                 /* Find valid DNS label */
                 prev_offset = offset;
                 offset = dns_label ( name, prev_offset );
                 if ( offset < 0 )
                         return offset;
 
                 /* Terminate if we have reached a compression pointer */
                 if ( offset != prev_offset )
                         return ( prev_offset + sizeof ( uint16_t ) );
 
                 /* Skip this label */
                 label = ( name->data + offset );
                 label_len = *label;
                 offset += ( sizeof ( *label ) + label_len );
 
                 /* Terminate if we have reached the root */
                 if ( label_len == 0 )
                         return offset;
         }
 
         /* Recursion limit exceeded */
         return -EINVAL;
 }

References dns_label(), EINVAL, name, and offset.

Referenced by dns_list_okx(), dns_skip_search(), and dns_xfer_deliver().

Data Structures

Macros

Functions

Detailed Description

Macro Definition Documentation

◆ DNS_PORT

◆ DNS_IS_COMPRESSED

◆ DNS_COMPRESSED_OFFSET

◆ DNS_LABEL_LEN

◆ DNS_MAX_LABEL_LEN

◆ DNS_MAX_NAME_LEN

◆ DNS_MAX_CNAME_RECURSION

◆ DNS_FLAG_RD

◆ DNS_CLASS_IN

◆ DNS_TYPE_A

◆ DNS_TYPE_AAAA

◆ DNS_TYPE_CNAME

Function Documentation

◆ FILE_LICENCE()

◆ dns_encode()

◆ dns_decode()

◆ dns_compare()

◆ dns_copy()

◆ dns_skip()