dhcpopts.c File Reference

DHCP options. More...

#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <ipxe/dhcp.h>
#include <ipxe/dhcpopts.h>

Go to the source code of this file.

Functions
	FILE_LICENCE (GPL2_OR_LATER_OR_UBDL)
	FILE_SECBOOT (PERMITTED)
static char *	dhcp_tag_name (unsigned int tag)
	Obtain printable version of a DHCP option tag. More...
static struct dhcp_option *	dhcp_option (struct dhcp_options *options, unsigned int offset)
	Get pointer to DHCP option. More...
static int	dhcp_option_offset (struct dhcp_options *options, struct dhcp_option *option)
	Get offset of a DHCP option. More...
static unsigned int	dhcp_option_len (struct dhcp_option *option)
	Calculate length of any DHCP option. More...
static int	find_dhcp_option_with_encap (struct dhcp_options *options, unsigned int tag, int *encap_offset)
	Find DHCP option within DHCP options block, and its encapsulator (if any) More...
int	dhcpopt_no_realloc (struct dhcp_options *options, size_t len)
	Refuse to reallocate DHCP option block. More...
static int	resize_dhcp_option (struct dhcp_options *options, int offset, int encap_offset, size_t old_len, size_t new_len)
	Resize a DHCP option. More...
static int	set_dhcp_option (struct dhcp_options *options, unsigned int tag, const void *data, size_t len)
	Set value of DHCP option. More...
int	dhcpopt_applies (unsigned int tag)
	Check applicability of DHCP option setting. More...
int	dhcpopt_store (struct dhcp_options *options, unsigned int tag, const void *data, size_t len)
	Store value of DHCP option setting. More...
int	dhcpopt_fetch (struct dhcp_options *options, unsigned int tag, void *data, size_t len)
	Fetch value of DHCP option setting. More...
void	dhcpopt_update_used_len (struct dhcp_options *options)
	Recalculate length of DHCP options block. More...
void	dhcpopt_init (struct dhcp_options *options, void *data, size_t alloc_len, int(*realloc)(struct dhcp_options *options, size_t len))
	Initialise prepopulated block of DHCP options. More...

Detailed Description

DHCP options.

Definition in file dhcpopts.c.

Function Documentation

FILE_LICENCE()

FILE_LICENCE

(

GPL2_OR_LATER_OR_UBDL

)

FILE_SECBOOT()

FILE_SECBOOT

(

PERMITTED

)

dhcp_tag_name()

static char* dhcp_tag_name ( unsigned int  tag )

inlinestatic

Obtain printable version of a DHCP option tag.

Parameters

tag	DHCP option tag

Return values

name	String representation of the tag

Definition at line 48 of file dhcpopts.c.

                                                        {
        static char name[8];

        if ( DHCP_IS_ENCAP_OPT ( tag ) ) {
                snprintf ( name, sizeof ( name ), "%d.%d",
                           DHCP_ENCAPSULATOR ( tag ),
                           DHCP_ENCAPSULATED ( tag ) );
        } else {
                snprintf ( name, sizeof ( name ), "%d", tag );
        }
        return name;
}

References DHCP_ENCAPSULATED, DHCP_ENCAPSULATOR, DHCP_IS_ENCAP_OPT, name, snprintf(), and tag.

Referenced by find_dhcp_option_with_encap(), and set_dhcp_option().

dhcp_option()

static struct dhcp_option* dhcp_option ( struct dhcp_options *  options, unsigned int  offset  )

inlinestatic

Get pointer to DHCP option.

Parameters

options	DHCP options block
offset	Offset within options block

Return values

option

DHCP option

Definition at line 69 of file dhcpopts.c.

                                                                  {
        return ( ( struct dhcp_option * ) ( options->data + offset ) );
}

References offset, and options.

Referenced by dhcpopt_fetch(), dhcpopt_update_used_len(), find_dhcp_option_with_encap(), resize_dhcp_option(), and set_dhcp_option().

dhcp_option_offset()

static int dhcp_option_offset ( struct dhcp_options *  options, struct dhcp_option *  option  )

inlinestatic

Get offset of a DHCP option.

Parameters

options	DHCP options block
option	DHCP option

Return values

offset

Offset within options block

Definition at line 81 of file dhcpopts.c.

                                                  {
        return ( ( ( void * ) option ) - options->data );
}

References options.

dhcp_option_len()

static unsigned int dhcp_option_len ( struct dhcp_option *  option )

static

Calculate length of any DHCP option.

Parameters

option

DHCP option

Return values

len	Length (including tag and length field)

Definition at line 92 of file dhcpopts.c.

                                                                   {
        if ( ( option->tag == DHCP_END ) || ( option->tag == DHCP_PAD ) ) {
                return 1;
        } else {
                return ( option->len + DHCP_OPTION_HEADER_LEN );
        }
}

References DHCP_END, DHCP_OPTION_HEADER_LEN, and DHCP_PAD.

Referenced by dhcpopt_update_used_len(), find_dhcp_option_with_encap(), and set_dhcp_option().

find_dhcp_option_with_encap()

static int find_dhcp_option_with_encap ( struct dhcp_options *  options, unsigned int  tag, int *  encap_offset  )

static

Find DHCP option within DHCP options block, and its encapsulator (if any)

Parameters

options	DHCP options block
tag	DHCP option tag to search for

Return values

encap_offset	Offset of encapsulating DHCP option
offset	Offset of DHCP option, or negative error

Searches for the DHCP option matching the specified tag within the DHCP option block. Encapsulated options may be searched for by using DHCP_ENCAP_OPT() to construct the tag value.

If the option is encapsulated, and encap_offset is non-NULL, it will be filled in with the offset of the encapsulating option.

This routine is designed to be paranoid. It does not assume that the option data is well-formatted, and so must guard against flaws such as options missing a DHCP_END terminator, or options whose length would take them beyond the end of the data block.

Definition at line 120 of file dhcpopts.c.

                                                             {
        unsigned int original_tag __attribute__ (( unused )) = tag;
        struct dhcp_option *option;
        int offset = 0;
        ssize_t remaining = options->used_len;
        unsigned int option_len;

        /* Sanity check */
        if ( tag == DHCP_PAD )
                return -ENOENT;

        /* Search for option */
        while ( remaining ) {
                /* Calculate length of this option.  Abort processing
                 * if the length is malformed (i.e. takes us beyond
                 * the end of the data block).
                 */
                option = dhcp_option ( options, offset );
                option_len = dhcp_option_len ( option );
                remaining -= option_len;
                if ( remaining < 0 )
                        break;
                /* Check for explicit end marker */
                if ( option->tag == DHCP_END ) {
                        if ( tag == DHCP_END )
                                /* Special case where the caller is interested
                                 * in whether we have this marker or not.
                                 */
                                return offset;
                        else
                                break;
                }
                /* Check for matching tag */
                if ( option->tag == tag ) {
                        DBGC ( options, "DHCPOPT %p found %s (length %d)\n",
                               options, dhcp_tag_name ( original_tag ),
                               option_len );
                        return offset;
                }
                /* Check for start of matching encapsulation block */
                if ( DHCP_IS_ENCAP_OPT ( tag ) &&
                     ( option->tag == DHCP_ENCAPSULATOR ( tag ) ) ) {
                        if ( encap_offset )
                                *encap_offset = offset;
                        /* Continue search within encapsulated option block */
                        tag = DHCP_ENCAPSULATED ( tag );
                        remaining = option_len;
                        offset += DHCP_OPTION_HEADER_LEN;
                        continue;
                }
                offset += option_len;
        }

        return -ENOENT;
}

References __attribute__, DBGC, DHCP_ENCAPSULATED, DHCP_ENCAPSULATOR, DHCP_END, DHCP_IS_ENCAP_OPT, dhcp_option(), DHCP_OPTION_HEADER_LEN, dhcp_option_len(), DHCP_PAD, dhcp_tag_name(), ENOENT, offset, options, tag, and unused.

Referenced by dhcpopt_fetch(), and set_dhcp_option().

dhcpopt_no_realloc()

int dhcpopt_no_realloc	(	struct dhcp_options *	options,
		size_t	len
	)

Refuse to reallocate DHCP option block.

Parameters

options	DHCP option block
len	New length

Return values

rc	Return status code

Definition at line 185 of file dhcpopts.c.

                                                                    {
        return ( ( len <= options->alloc_len ) ? 0 : -ENOSPC );
}

References ENOSPC.

Referenced by dhcppkt_init(), and nvo_realloc_dhcpopt().

resize_dhcp_option()

static int resize_dhcp_option ( struct dhcp_options *  options, int  offset, int  encap_offset, size_t  old_len, size_t  new_len  )

static

Resize a DHCP option.

Parameters

options	DHCP option block
offset	Offset of option to resize
encap_offset	Offset of encapsulating offset (or -ve for none)
old_len	Old length (including header)
new_len	New length (including header)

Return values

rc	Return status code

Definition at line 199 of file dhcpopts.c.

                                                                 {
        struct dhcp_option *encapsulator;
        struct dhcp_option *option;
        ssize_t delta = ( new_len - old_len );
        size_t old_alloc_len;
        size_t new_used_len;
        size_t new_encapsulator_len;
        void *source;
        void *dest;
        int rc;

        /* Check for sufficient space */
        if ( new_len > DHCP_MAX_LEN ) {
                DBGC ( options, "DHCPOPT %p overlength option\n", options );
                return -ENOSPC;
        }
        new_used_len = ( options->used_len + delta );

        /* Expand options block, if necessary */
        if ( new_used_len > options->alloc_len ) {
                /* Reallocate options block */
                old_alloc_len = options->alloc_len;
                if ( ( rc = options->realloc ( options, new_used_len ) ) != 0 ){
                        DBGC ( options, "DHCPOPT %p could not reallocate to "
                               "%zd bytes\n", options, new_used_len );
                        return rc;
                }
                /* Clear newly allocated space */
                memset ( ( options->data + old_alloc_len ), 0,
                         ( options->alloc_len - old_alloc_len ) );
        }

        /* Update encapsulator, if applicable */
        if ( encap_offset >= 0 ) {
                encapsulator = dhcp_option ( options, encap_offset );
                new_encapsulator_len = ( encapsulator->len + delta );
                if ( new_encapsulator_len > DHCP_MAX_LEN ) {
                        DBGC ( options, "DHCPOPT %p overlength encapsulator\n",
                               options );
                        return -ENOSPC;
                }
                encapsulator->len = new_encapsulator_len;
        }

        /* Update used length */
        options->used_len = new_used_len;

        /* Move remainder of option data */
        option = dhcp_option ( options, offset );
        source = ( ( ( void * ) option ) + old_len );
        dest = ( ( ( void * ) option ) + new_len );
        memmove ( dest, source, ( new_used_len - offset - new_len ) );

        /* Shrink options block, if applicable */
        if ( new_used_len < options->alloc_len ) {
                if ( ( rc = options->realloc ( options, new_used_len ) ) != 0 ){
                        DBGC ( options, "DHCPOPT %p could not reallocate to "
                               "%zd bytes\n", options, new_used_len );
                        return rc;
                }
        }

        return 0;
}

References DBGC, dest, DHCP_MAX_LEN, dhcp_option(), ENOSPC, dhcp_option::len, memmove(), memset(), offset, options, and rc.

Referenced by set_dhcp_option().

set_dhcp_option()

static int set_dhcp_option ( struct dhcp_options *  options, unsigned int  tag, const void *  data, size_t  len  )

static

Set value of DHCP option.

Parameters

options	DHCP option block
tag	DHCP option tag
data	New value for DHCP option
len	Length of value, in bytes

Return values

offset

Offset of DHCP option, or negative error

Sets the value of a DHCP option within the options block. The option may or may not already exist. Encapsulators will be created (and deleted) as necessary.

This call may fail due to insufficient space in the options block. If it does fail, and the option existed previously, the option will be left with its original value.

Definition at line 283 of file dhcpopts.c.

                                                            {
        static const uint8_t empty_encap[] = { DHCP_END };
        int offset;
        int encap_offset = -1;
        int creation_offset;
        struct dhcp_option *option;
        unsigned int encap_tag = DHCP_ENCAPSULATOR ( tag );
        size_t old_len = 0;
        size_t new_len = ( len ? ( len + DHCP_OPTION_HEADER_LEN ) : 0 );
        int rc;

        /* Sanity check */
        if ( tag == DHCP_PAD )
                return -ENOTTY;

        creation_offset = find_dhcp_option_with_encap ( options, DHCP_END,
                                                        NULL );
        if ( creation_offset < 0 )
                creation_offset = options->used_len;
        /* Find old instance of this option, if any */
        offset = find_dhcp_option_with_encap ( options, tag, &encap_offset );
        if ( offset >= 0 ) {
                old_len = dhcp_option_len ( dhcp_option ( options, offset ) );
                DBGC ( options, "DHCPOPT %p resizing %s from %zd to %zd\n",
                       options, dhcp_tag_name ( tag ), old_len, new_len );
        } else {
                DBGC ( options, "DHCPOPT %p creating %s (length %zd)\n",
                       options, dhcp_tag_name ( tag ), new_len );
        }

        /* Ensure that encapsulator exists, if required */
        if ( encap_tag ) {
                if ( encap_offset < 0 ) {
                        encap_offset =
                                set_dhcp_option ( options, encap_tag,
                                                  empty_encap,
                                                  sizeof ( empty_encap ) );
                }
                if ( encap_offset < 0 )
                        return encap_offset;
                creation_offset = ( encap_offset + DHCP_OPTION_HEADER_LEN );
        }

        /* Create new option if necessary */
        if ( offset < 0 )
                offset = creation_offset;

        /* Resize option to fit new data */
        if ( ( rc = resize_dhcp_option ( options, offset, encap_offset,
                                         old_len, new_len ) ) != 0 )
                return rc;

        /* Copy new data into option, if applicable */
        if ( len ) {
                option = dhcp_option ( options, offset );
                option->tag = tag;
                option->len = len;
                memcpy ( &option->data, data, len );
        }

        /* Delete encapsulator if there's nothing else left in it */
        if ( encap_offset >= 0 ) {
                option = dhcp_option ( options, encap_offset );
                if ( option->len <= 1 )
                        set_dhcp_option ( options, encap_tag, NULL, 0 );
        }

        return offset;
}

References data, DBGC, DHCP_ENCAPSULATOR, DHCP_END, dhcp_option(), DHCP_OPTION_HEADER_LEN, dhcp_option_len(), DHCP_PAD, dhcp_tag_name(), ENOTTY, find_dhcp_option_with_encap(), len, memcpy(), NULL, offset, options, rc, resize_dhcp_option(), and tag.

Referenced by dhcpopt_store().

dhcpopt_applies()

int dhcpopt_applies

(

unsigned int

tag

)

Check applicability of DHCP option setting.

Parameters

tag	Setting tag number

Return values

applies

Setting applies to this option block

Definition at line 360 of file dhcpopts.c.

                                         {

        return ( tag && ( tag <= DHCP_ENCAP_OPT ( DHCP_MAX_OPTION,
                                                  DHCP_MAX_OPTION ) ) );
}

References DHCP_ENCAP_OPT, DHCP_MAX_OPTION, and tag.

Referenced by dhcppkt_applies(), and nvo_applies().

dhcpopt_store()

int dhcpopt_store	(	struct dhcp_options *	options,
		unsigned int	tag,
		const void *	data,
		size_t	len
	)

Store value of DHCP option setting.

Parameters

options	DHCP option block
tag	Setting tag number
data	Setting data, or NULL to clear setting
len	Length of setting data

Return values

rc	Return status code

Definition at line 375 of file dhcpopts.c.

                                                   {
        int offset;

        offset = set_dhcp_option ( options, tag, data, len );
        if ( offset < 0 )
                return offset;
        return 0;
}

References data, len, offset, options, set_dhcp_option(), and tag.

Referenced by dhcppkt_store(), and nvo_store().

dhcpopt_fetch()

int dhcpopt_fetch	(	struct dhcp_options *	options,
		unsigned int	tag,
		void *	data,
		size_t	len
	)

Fetch value of DHCP option setting.

Parameters

options	DHCP option block
tag	Setting tag number
data	Buffer to fill with setting data
len	Length of buffer

Return values

len	Length of setting data, or negative error

Definition at line 394 of file dhcpopts.c.

                                             {
        int offset;
        struct dhcp_option *option;
        size_t option_len;

        offset = find_dhcp_option_with_encap ( options, tag, NULL );
        if ( offset < 0 )
                return offset;

        option = dhcp_option ( options, offset );
        option_len = option->len;
        if ( len > option_len )
                len = option_len;
        memcpy ( data, option->data, len );

        return option_len;
}

References data, dhcp_option(), find_dhcp_option_with_encap(), len, memcpy(), NULL, offset, options, and tag.

Referenced by dhcppkt_fetch(), and nvo_fetch().

dhcpopt_update_used_len()

void dhcpopt_update_used_len

(

struct dhcp_options *

options

)

Recalculate length of DHCP options block.

Parameters

options

Uninitialised DHCP option block

The "used length" field will be updated based on scanning through the block to find the end of the options.

Definition at line 421 of file dhcpopts.c.

                                                              {
        struct dhcp_option *option;
        int offset = 0;
        ssize_t remaining = options->alloc_len;
        unsigned int option_len;

        /* Find last non-pad option */
        options->used_len = 0;
        while ( remaining ) {
                option = dhcp_option ( options, offset );
                option_len = dhcp_option_len ( option );
                remaining -= option_len;
                if ( remaining < 0 )
                        break;
                offset += option_len;
                if ( option->tag != DHCP_PAD )
                        options->used_len = offset;
        }
}

References dhcp_option(), dhcp_option_len(), DHCP_PAD, offset, and options.

Referenced by dhcpopt_init(), and nvo_load().

dhcpopt_init()

void dhcpopt_init	(	struct dhcp_options *	options,
		void *	data,
		size_t	alloc_len,
		int(*)(struct dhcp_options *options, size_t len)	realloc
	)

Initialise prepopulated block of DHCP options.

Parameters

options	Uninitialised DHCP option block
data	Memory for DHCP option data
alloc_len	Length of memory for DHCP option data
realloc	DHCP option block reallocator

The memory content must already be filled with valid DHCP options. A zeroed block counts as a block of valid DHCP options.

Definition at line 452 of file dhcpopts.c.

                                                       {

        /* Fill in fields */
        options->data = data;
        options->alloc_len = alloc_len;
        options->realloc = realloc;

        /* Update length */
        dhcpopt_update_used_len ( options );

        DBGC ( options, "DHCPOPT %p created (data %p lengths %#zx,%#zx)\n",
               options, options->data, options->used_len, options->alloc_len );
}

References data, DBGC, dhcpopt_update_used_len(), options, and realloc().

Referenced by dhcppkt_init(), and nvo_init().