[PXE] Work around a buffer-size bug in WinPE

[people/dverkamp/gpxe.git] / src / interface / pxe / pxe_preboot.c

diff --git a/src/interface/pxe/pxe_preboot.c b/src/interface/pxe/pxe_preboot.c
index 53ece3c..2d6f135 100644 (file)
--- a/src/interface/pxe/pxe_preboot.c
+++ b/src/interface/pxe/pxe_preboot.c
@@ -51,8 +51,18 @@ enum pxe_cached_info_indices {
 /** A cached DHCP packet */
 union pxe_cached_info {
        struct dhcphdr dhcphdr;
 /** A cached DHCP packet */
 union pxe_cached_info {
        struct dhcphdr dhcphdr;

-       char raw[ETH_FRAME_LEN];
-};
+       /* This buffer must be *exactly* the size of a BOOTPLAYER_t
+        * structure, otherwise WinPE will die horribly.  It takes the
+        * size of *our* buffer and feeds it in to us as the size of
+        * one of *its* buffers.  If our buffer is larger than it
+        * expects, we therefore end up overwriting part of its data
+        * segment, since it tells us to do so.  (D'oh!)
+        *
+        * Note that a BOOTPLAYER_t is not necessarily large enough to
+        * hold a DHCP packet; this is a flaw in the PXE spec.
+        */
+       BOOTPLAYER_t packet;
+} __attribute__ (( packed ));

 
 /* The case in which the caller doesn't supply a buffer is really
  * awkward to support given that we have 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,