commit 8f1c1201199a924eeba31494be5aa6bf13eb3fa0
author Michael Brown <mcb30@ipxe.org> Wed Mar 08 00:43:33 2023 +0000
committer Michael Brown <mcb30@ipxe.org> Tue Mar 14 11:35:30 2023 +0000
tree 7f42f39cbd8bbfc834da9bb85a2602d084a5f844
parent 54fcb7c29ce2fabe109286e3c4dfeb297e0f3916

[dhcp] Unregister ProxyDHCP and PXEBS settings on a successful DHCPACK

When a DHCP transaction does not result in the registration of a new
"proxydhcp" or "pxebs" settings block, any existing settings blocks
are currently left unaltered.

This can cause surprising behaviour.  For example: when chainloading
iPXE, the "proxydhcp" and "pxebs" settings blocks may be prepopulated
using cached values from the previous PXE bootloader.  If iPXE
performs a subsequent DHCP request, then the DHCP or ProxyDHCP servers
may choose to respond differently to iPXE.  The response may choose to
omit the ProxyDHCP or PXEBS stages, in which case no new "proxydhcp"
or "pxebs" settings blocks may be registered.  This will result in
iPXE using a combination of both old and new DHCP responses.

Fix by assuming that a successful DHCPACK effectively acquires
ownership of the "proxydhcp" and "pxebs" settings blocks, and that any
existing settings blocks should therefore be unregistered.

Reported-by: Henry Tung <htung@palantir.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>