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[pxe] Clarify comments regarding shrinking of cached DHCP packet 

Signed-off-by: Michael Brown <mcb30@ipxe.org>
pull/45/head
Michael Brown 2016-02-11 19:14:00 +00:00
parent 12b3b57886
commit 6de378aae8
1 changed files with 9 additions and 6 deletions
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15
src/arch/i386/core/cachedhcp.c
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@ -58,6 +58,7 @@ static void cachedhcp_init ( void ) {
struct dhcp_packet *dhcppkt; struct dhcp_packet *dhcppkt;
struct dhcp_packet *tmp; struct dhcp_packet *tmp;
struct dhcphdr *dhcphdr; struct dhcphdr *dhcphdr;
size_t max_len;
size_t len; size_t len;
/* Do nothing if no cached DHCPACK is present */ /* Do nothing if no cached DHCPACK is present */
@ -69,23 +70,25 @@ static void cachedhcp_init ( void ) {
/* No reliable way to determine length before parsing packet; /* No reliable way to determine length before parsing packet;
* start by assuming maximum length permitted by PXE. * start by assuming maximum length permitted by PXE.
*/ */
len = sizeof ( BOOTPLAYER_t ); max_len = sizeof ( BOOTPLAYER_t );
/* Allocate and populate DHCP packet */ /* Allocate and populate DHCP packet */
dhcppkt = zalloc ( sizeof ( *dhcppkt ) + len ); dhcppkt = zalloc ( sizeof ( *dhcppkt ) + max_len );
if ( ! dhcppkt ) { if ( ! dhcppkt ) {
DBGC ( colour, "CACHEDHCP could not allocate copy\n" ); DBGC ( colour, "CACHEDHCP could not allocate copy\n" );
return; return;
} }
dhcphdr = ( ( ( void * ) dhcppkt ) + sizeof ( *dhcppkt ) ); dhcphdr = ( ( ( void * ) dhcppkt ) + sizeof ( *dhcppkt ) );
copy_from_user ( dhcphdr, phys_to_user ( cached_dhcpack_phys ), 0, copy_from_user ( dhcphdr, phys_to_user ( cached_dhcpack_phys ), 0,
len ); max_len );
dhcppkt_init ( dhcppkt, dhcphdr, len ); dhcppkt_init ( dhcppkt, dhcphdr, max_len );
/* Resize packet to required length. If reallocation fails, /* Shrink packet to required length. If reallocation fails,
* just continue to use the original packet. * just continue to use the original packet and waste the
* unused space.
*/ */
len = dhcppkt_len ( dhcppkt ); len = dhcppkt_len ( dhcppkt );
assert ( len <= max_len );
tmp = realloc ( dhcppkt, ( sizeof ( *dhcppkt ) + len ) ); tmp = realloc ( dhcppkt, ( sizeof ( *dhcppkt ) + len ) );
if ( tmp ) if ( tmp )
dhcppkt = tmp; dhcppkt = tmp;