NetworkPkg: UefiPxeBcDxe: SECURITY PATCH CVE-2023-45234 Patch

REF:https://bugzilla.tianocore.org/show_bug.cgi?id=4539

Bug Details:
PixieFail Bug #6
CVE-2023-45234
CVSS 8.3 : CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:H
CWE-119 Improper Restriction of Operations within the Bounds of
 a Memory Buffer

Buffer overflow when processing DNS Servers option in a DHCPv6
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Change Overview:

Introduces a function to cache the Dns Server and perform sanitizing
on the incoming DnsServerLen to ensure that the length is valid

> + EFI_STATUS
> + PxeBcCacheDnsServerAddresses (
> +  IN PXEBC_PRIVATE_DATA        *Private,
> +  IN PXEBC_DHCP6_PACKET_CACHE  *Cache6
> +  )

Additional code cleanup

Cc: Saloni Kasbekar <[email protected]>
Cc: Zachary Clark-williams <[email protected]>

Signed-off-by: Doug Flick [MSFT] <[email protected]>
Reviewed-by: Saloni Kasbekar <[email protected]>

NetworkPkg/UefiPxeBcDxe/PxeBcDhcp6.c

@@ -3,6 +3,7 @@
 
   (C) Copyright 2014 Hewlett-Packard Development Company, L.P.<BR>
   Copyright (c) 2009 - 2018, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) Microsoft Corporation
 
   SPDX-License-Identifier: BSD-2-Clause-Patent
 
@@ -1312,6 +1313,65 @@ PxeBcSelectDhcp6Offer (
   }
 }
 
+/**
+  Cache the DHCPv6 DNS Server addresses
+
+  @param[in] Private               The pointer to PXEBC_PRIVATE_DATA.
+  @param[in] Cache6                The pointer to PXEBC_DHCP6_PACKET_CACHE.
+
+  @retval    EFI_SUCCESS           Cache the DHCPv6 DNS Server address successfully.
+  @retval    EFI_OUT_OF_RESOURCES  Failed to allocate resources.
+  @retval    EFI_DEVICE_ERROR      The DNS Server Address Length provided by a untrusted
+                                   option is not a multiple of 16 bytes (sizeof (EFI_IPv6_ADDRESS)).
+**/
+EFI_STATUS
+PxeBcCacheDnsServerAddresses (
+  IN PXEBC_PRIVATE_DATA        *Private,
+  IN PXEBC_DHCP6_PACKET_CACHE  *Cache6
+  )
+{
+  UINT16  DnsServerLen;
+
+  DnsServerLen = NTOHS (Cache6->OptList[PXEBC_DHCP6_IDX_DNS_SERVER]->OpLen);
+  //
+  // Make sure that the number is nonzero
+  //
+  if (DnsServerLen == 0) {
+    return EFI_DEVICE_ERROR;
+  }
+
+  //
+  // Make sure the DnsServerlen is a multiple of EFI_IPv6_ADDRESS (16)
+  //
+  if (DnsServerLen % sizeof (EFI_IPv6_ADDRESS) != 0) {
+    return EFI_DEVICE_ERROR;
+  }
+
+  //
+  // This code is currently written to only support a single DNS Server instead
+  // of multiple such as is spec defined (RFC3646, Section 3). The proper behavior
+  // would be to allocate the full space requested, CopyMem all of the data,
+  // and then add a DnsServerCount field to Private and update additional code
+  // that depends on this.
+  //
+  // To support multiple DNS servers the `AllocationSize` would need to be changed to DnsServerLen
+  //
+  // This is tracked in https://bugzilla.tianocore.org/show_bug.cgi?id=1886
+  //
+  Private->DnsServer = AllocateZeroPool (sizeof (EFI_IPv6_ADDRESS));
+  if (Private->DnsServer == NULL) {
+    return EFI_OUT_OF_RESOURCES;
+  }
+
+  //
+  // Intentionally only copy over the first server address.
+  // To support multiple DNS servers, the `Length` would need to be changed to DnsServerLen
+  //
+  CopyMem (Private->DnsServer, Cache6->OptList[PXEBC_DHCP6_IDX_DNS_SERVER]->Data, sizeof (EFI_IPv6_ADDRESS));
+
+  return EFI_SUCCESS;
+}
+
 /**
   Handle the DHCPv6 offer packet.
 
@@ -1335,22 +1395,21 @@ PxeBcHandleDhcp6Offer (
   UINT32                    SelectIndex;
   UINT32                    Index;
 
+  ASSERT (Private != NULL);
   ASSERT (Private->SelectIndex > 0);
   SelectIndex = (UINT32)(Private->SelectIndex - 1);
   ASSERT (SelectIndex < PXEBC_OFFER_MAX_NUM);
   Cache6 = &Private->OfferBuffer[SelectIndex].Dhcp6;
   Status = EFI_SUCCESS;
 
   //
-  // First try to cache DNS server address if DHCP6 offer provides.
+  // First try to cache DNS server addresses if DHCP6 offer provides.
   //
   if (Cache6->OptList[PXEBC_DHCP6_IDX_DNS_SERVER] != NULL) {
-    Private->DnsServer = AllocateZeroPool (NTOHS (Cache6->OptList[PXEBC_DHCP6_IDX_DNS_SERVER]->OpLen));
-    if (Private->DnsServer == NULL) {
-      return EFI_OUT_OF_RESOURCES;
+    Status = PxeBcCacheDnsServerAddresses (Private, Cache6);
+    if (EFI_ERROR (Status)) {
+      return Status;
     }
-
-    CopyMem (Private->DnsServer, Cache6->OptList[PXEBC_DHCP6_IDX_DNS_SERVER]->Data, sizeof (EFI_IPv6_ADDRESS));
   }
 
   if (Cache6->OfferType == PxeOfferTypeDhcpBinl) {