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Do not fill in the BufferLimit field in struct

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s_PXENV_GET_CACHED_INFO, because this field doesn't exist in earlier
versions of the PXE spec, and some callers don't allocate space for it.
This commit is contained in:
Michael Brown 2007-11-22 00:31:21 +00:00
parent b3abf25e3c
commit 3a2473f123
1 changed files with 32 additions and 3 deletions
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35
src/interface/pxe/pxe_preboot.c
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@ -83,8 +83,33 @@ PXENV_EXIT_t pxenv_get_cached_info ( struct s_PXENV_GET_CACHED_INFO
DBG ( " to %04x:%04x+%x", get_cached_info->Buffer.segment,
get_cached_info->Buffer.offset, get_cached_info->BufferSize );
/* This is really, really awkward to support with our multiple
* sources of options.
/* The case in which the caller doesn't supply a buffer is
* really awkward to support given that we have multiple
* sources of options, and that we don't actually store the
* DHCP packets. (We may not even have performed DHCP; we may
* have obtained all configuration from non-volatile stored
* options or from the command line.) We provide the caller
* with our base-memory temporary packet buffer and construct
* the packet in there.
*
* To add to the fun, Intel decided at some point in the
* evolution of the PXE specification to add the BufferLimit
* field, which we are meant to fill in with the length of our
* packet buffer, so that the caller can safely modify the
* boot server reply packet stored therein. However, this
* field was not present in earlier versions of the PXE spec,
* and there is at least one PXE NBP (Altiris) which allocates
* only exactly enough space for this earlier, shorter version
* of the structure. If we actually fill in the BufferLimit
* field, we therefore risk trashing random areas of the
* caller's memory. If we *don't* fill it in, then the caller
* is at liberty to assume that whatever random value happened
* to be in that location represents the length of the buffer
* we've just passed back to it.
*
* Since older PXE stacks won't fill this field in anyway,
* it's probably safe to assume that no callers actually rely
* on it, so we choose to not fill it in.
*/
len = get_cached_info->BufferSize;
if ( len == 0 ) {
@ -92,7 +117,9 @@ PXENV_EXIT_t pxenv_get_cached_info ( struct s_PXENV_GET_CACHED_INFO
get_cached_info->Buffer.segment = rm_ds;
get_cached_info->Buffer.offset =
( unsigned int ) ( & __from_data16 ( basemem_packet ) );
get_cached_info->BufferLimit = len;
DBG ( " using %04x:%04x+'%x'", get_cached_info->Buffer.segment,
get_cached_info->Buffer.offset,
get_cached_info->BufferLimit );
}
/* Allocate space for temporary copy */
@ -118,6 +145,7 @@ PXENV_EXIT_t pxenv_get_cached_info ( struct s_PXENV_GET_CACHED_INFO
/* Overwrite filename to work around Microsoft RIS bug */
if ( pxe_ris_filename ) {
DBG ( " applying RIS hack" );
strncpy ( dhcppkt.dhcphdr->file, pxe_ris_filename,
sizeof ( dhcppkt.dhcphdr->file ) );
}
@ -126,6 +154,7 @@ PXENV_EXIT_t pxenv_get_cached_info ( struct s_PXENV_GET_CACHED_INFO
buffer = real_to_user ( get_cached_info->Buffer.segment,
get_cached_info->Buffer.offset );
len = dhcppkt.len;
DBG ( " length %x", len );
copy_to_user ( buffer, 0, data, len );
get_cached_info->BufferSize = len;