From 3f55418d5396629c4458061f283068b6c46895fc Mon Sep 17 00:00:00 2001 From: Laszlo Ersek Date: Tue, 31 Mar 2020 02:47:49 +0200 Subject: [PATCH] NetworkPkg/UefiPxeBcDxe: handle competing DHCP servers (more) gracefully MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit When DHCP is misconfigured on a network segment, such that two DHCP servers attempt to reply to requests (and therefore race with each other), the edk2 PXE client can confuse itself. In PxeBcDhcp4BootInfo() / PxeBcDhcp6BootInfo(), the client may refer to a DHCP reply packet as an "earlier" packet from the "same" DHCP server, when in reality both packets are unrelated, and arrive from different DHCP servers. While the edk2 PXE client can do nothing to fix this, it should at least not ASSERT() -- ASSERT() is for catching programming errors (violations of invariants that are under the control of the programmer). ASSERT()s should in particular not refer to external data (such as network packets). What's more, in RELEASE builds, we get NULL pointer references. Check the problem conditions with actual "if"s, and return EFI_PROTOCOL_ERROR. This will trickle out to PxeBcLoadBootFile(), and be reported as "PXE-E99: Unexpected network error". Cc: Jiaxin Wu Cc: Maciej Rabeda Cc: Philippe Mathieu-Daudé Cc: Siyuan Fu Signed-off-by: Laszlo Ersek Message-Id: <20200331004749.16128-1-lersek@redhat.com> Reviewed-by: Siyuan Fu Reviewed-by: Maciej Rabeda --- NetworkPkg/UefiPxeBcDxe/PxeBcBoot.c | 30 +++++++++++++++++++++++++++-- 1 file changed, 28 insertions(+), 2 deletions(-) diff --git a/NetworkPkg/UefiPxeBcDxe/PxeBcBoot.c b/NetworkPkg/UefiPxeBcDxe/PxeBcBoot.c index 10bbb06f75..d062a52607 100644 --- a/NetworkPkg/UefiPxeBcDxe/PxeBcBoot.c +++ b/NetworkPkg/UefiPxeBcDxe/PxeBcBoot.c @@ -482,7 +482,20 @@ PxeBcDhcp4BootInfo ( Cache4 = &Private->DhcpAck.Dhcp4; } - ASSERT (Cache4->OptList[PXEBC_DHCP4_TAG_INDEX_BOOTFILE] != NULL); + if (Cache4->OptList[PXEBC_DHCP4_TAG_INDEX_BOOTFILE] == NULL) { + // + // This should never happen in a correctly configured DHCP / PXE + // environment. One misconfiguration that can cause it is two DHCP servers + // mistakenly running on the same network segment at the same time, and + // racing each other in answering DHCP requests. Thus, the DHCP packets + // that the edk2 PXE client considers "belonging together" may actually be + // entirely independent, coming from two (competing) DHCP servers. + // + // Try to deal with this gracefully. Note that this check is not + // comprehensive, as we don't try to identify all such errors. + // + return EFI_PROTOCOL_ERROR; + } // // Parse the boot server address. @@ -612,7 +625,20 @@ PxeBcDhcp6BootInfo ( Cache6 = &Private->DhcpAck.Dhcp6; } - ASSERT (Cache6->OptList[PXEBC_DHCP6_IDX_BOOT_FILE_URL] != NULL); + if (Cache6->OptList[PXEBC_DHCP6_IDX_BOOT_FILE_URL] == NULL) { + // + // This should never happen in a correctly configured DHCP / PXE + // environment. One misconfiguration that can cause it is two DHCP servers + // mistakenly running on the same network segment at the same time, and + // racing each other in answering DHCP requests. Thus, the DHCP packets + // that the edk2 PXE client considers "belonging together" may actually be + // entirely independent, coming from two (competing) DHCP servers. + // + // Try to deal with this gracefully. Note that this check is not + // comprehensive, as we don't try to identify all such errors. + // + return EFI_PROTOCOL_ERROR; + } // // Set the station address to IP layer. -- 2.39.2