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[DHCP] Treat empty fields in DHCP packets as non-existent. 

This avoids confusing other code by insisting that we have e.g. a
filename consisting of 128 zero bytes.
This commit is contained in:
Michael Brown 2008-03-27 06:06:36 +00:00
parent 978996cdae
commit 7a4e212fe2
1 changed files with 48 additions and 10 deletions
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58
src/net/dhcppkt.c
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@ -32,6 +32,30 @@
*
*/
/**
* Calculate used length of an IPv4 field within a DHCP packet
*
* @v data Field data
* @v len Length of field
* @ret used Used length of field
*/
static size_t used_len_ipv4 ( const void *data, size_t len __unused ) {
const struct in_addr *in = data;
return ( in->s_addr ? sizeof ( *in ) : 0 );
}
/**
* Calculate used length of a string field within a DHCP packet
*
* @v data Field data
* @v len Length of field
* @ret used Used length of field
*/
static size_t used_len_string ( const void *data, size_t len ) {
return strnlen ( data, len );
}
/** A dedicated field within a DHCP packet */
struct dhcp_packet_field {
/** Settings tag number */
@ -40,25 +64,34 @@ struct dhcp_packet_field {
uint16_t offset;
/** Length of field */
uint16_t len;
/** Calculate used length of field
*
* @v data Field data
* @v len Length of field
* @ret used Used length of field
*/
size_t ( * used_len ) ( const void *data, size_t len );
};
/** Declare a dedicated field within a DHCP packet
*
* @v _tag Settings tag number
* @v _field Field name
* @v _used_len Function to calculate used length of field
*/
#define DHCP_PACKET_FIELD( _tag, _field ) { \
#define DHCP_PACKET_FIELD( _tag, _field, _used_len ) { \
.tag = (_tag), \
.offset = offsetof ( struct dhcphdr, _field ), \
.len = sizeof ( ( ( struct dhcphdr * ) 0 )->_field ), \
.used_len = _used_len, \
}
/** Dedicated fields within a DHCP packet */
static struct dhcp_packet_field dhcp_packet_fields[] = {
DHCP_PACKET_FIELD ( DHCP_EB_YIADDR, yiaddr ),
DHCP_PACKET_FIELD ( DHCP_EB_SIADDR, siaddr ),
DHCP_PACKET_FIELD ( DHCP_TFTP_SERVER_NAME, sname ),
DHCP_PACKET_FIELD ( DHCP_BOOTFILE_NAME, file ),
DHCP_PACKET_FIELD ( DHCP_EB_YIADDR, yiaddr, used_len_ipv4 ),
DHCP_PACKET_FIELD ( DHCP_EB_SIADDR, siaddr, used_len_ipv4 ),
DHCP_PACKET_FIELD ( DHCP_TFTP_SERVER_NAME, sname, used_len_string ),
DHCP_PACKET_FIELD ( DHCP_BOOTFILE_NAME, file, used_len_string ),
};
/**
@ -138,14 +171,19 @@ int dhcppkt_store ( struct dhcp_packet *dhcppkt, unsigned int tag,
int dhcppkt_fetch ( struct dhcp_packet *dhcppkt, unsigned int tag,
void *data, size_t len ) {
struct dhcp_packet_field *field;
void *field_data;
size_t field_len;
/* If this is a special field, return it */
if ( ( field = find_dhcp_packet_field ( tag ) ) != NULL ) {
if ( len > field->len )
len = field->len;
memcpy ( data,
dhcp_packet_field ( dhcppkt->dhcphdr, field ), len );
return field->len;
field_data = dhcp_packet_field ( dhcppkt->dhcphdr, field );
field_len = field->used_len ( field_data, field->len );
if ( ! field_len )
return -ENOENT;
if ( len > field_len )
len = field_len;
memcpy ( data, field_data, len );
return field_len;
}
/* Otherwise, use the generic options block */