[PATCH v1] NetworkPkg/DnsDxe: Check the received packet size before parsing the message.

[Jiaxin Wu <Jiaxin.wu@intel.com>]

Fix CVE-2018-12178
REF: https://bugzilla.tianocore.org/show_bug.cgi?id=809

The DNS driver only checks the received packet size against the
minimum DNS header size in DnsOnPacketReceived(), later it accesses
the QueryName and QuerySection beyond the header scope, which might
cause the pointer within DNS driver points to an invalid entry or
modifies the memory content beyond the header scope.

This patch is to fix above problem.

Cc: Ye Ting <ting.ye@intel.com>
Cc: Fu Siyuan <siyuan.fu@intel.com>
Cc: Wang Fan <fan.wang@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Wu Jiaxin <jiaxin.wu@intel.com>
---
 NetworkPkg/DnsDxe/DnsImpl.c | 77 ++++++++++++++++++++++++++++++++-----
 NetworkPkg/DnsDxe/DnsImpl.h |  2 +
 2 files changed, 69 insertions(+), 10 deletions(-)

diff --git a/NetworkPkg/DnsDxe/DnsImpl.c b/NetworkPkg/DnsDxe/DnsImpl.c
index 89ea755cb2..26a718987c 100644
--- a/NetworkPkg/DnsDxe/DnsImpl.c
+++ b/NetworkPkg/DnsDxe/DnsImpl.c
@@ -1112,26 +1112,29 @@ IsValidDnsResponse (
 /**
   Parse Dns Response.
 
   @param  Instance              The DNS instance
   @param  RxString              Received buffer.
+  @param  Length                Received buffer length.
   @param  Completed             Flag to indicate that Dns response is valid.
 
   @retval EFI_SUCCESS           Parse Dns Response successfully.
   @retval Others                Failed to parse Dns Response.
 
 **/
 EFI_STATUS
 ParseDnsResponse (
   IN OUT DNS_INSTANCE              *Instance,
   IN     UINT8                     *RxString,
+  IN     UINT32                    Length,
      OUT BOOLEAN                   *Completed
   )
 {
   DNS_HEADER            *DnsHeader;
 
   CHAR8                 *QueryName;
+  UINT32                QueryNameLen;
   DNS_QUERY_SECTION     *QuerySection;
 
   CHAR8                 *AnswerName;
   DNS_ANSWER_SECTION    *AnswerSection;
   UINT8                 *AnswerData;
@@ -1153,10 +1156,11 @@ ParseDnsResponse (
 
   DNS_RESOURCE_RECORD   *Dns4RR;
   DNS6_RESOURCE_RECORD  *Dns6RR;
 
   EFI_STATUS            Status;
+  UINT32                RemainingLength;
 
   EFI_TPL               OldTpl;
 
   Item             = NULL;
   Dns4TokenEntry   = NULL;
@@ -1176,10 +1180,21 @@ ParseDnsResponse (
   Dns4RR           = NULL;
   Dns6RR           = NULL;
 
   *Completed       = TRUE;
   Status           = EFI_SUCCESS;
+  RemainingLength  = Length;
+
+  //
+  // Check whether the remaining packet length is avaiable or not.
+  //
+  if (RemainingLength <= sizeof (DNS_HEADER)) {
+    *Completed = FALSE;
+    return EFI_ABORTED;
+  } else {
+    RemainingLength -= sizeof (DNS_HEADER);
+  }
 
   //
   // Get header
   //
   DnsHeader = (DNS_HEADER *) RxString;
@@ -1189,26 +1204,42 @@ ParseDnsResponse (
   DnsHeader->QuestionsNum = NTOHS (DnsHeader->QuestionsNum);
   DnsHeader->AnswersNum = NTOHS (DnsHeader->AnswersNum);
   DnsHeader->AuthorityNum = NTOHS (DnsHeader->AuthorityNum);
   DnsHeader->AditionalNum = NTOHS (DnsHeader->AditionalNum);
 
+  //
+  // There is always one QuestionsNum in DNS message. The capability to handle more
+  // than one requires to redesign the message format. Currently, it's not supported.
+  //
+  if (DnsHeader->QuestionsNum > 1) {
+    *Completed = FALSE;
+    return EFI_UNSUPPORTED;
+  }
+
   //
   // Get Query name
   //
   QueryName = (CHAR8 *) (RxString + sizeof (*DnsHeader));
 
+  QueryNameLen = (UINT32) AsciiStrLen (QueryName) + 1;
+
   //
-  // Get query section
+  // Check whether the remaining packet length is avaiable or not.
   //
-  QuerySection = (DNS_QUERY_SECTION *) (QueryName + AsciiStrLen (QueryName) + 1);
-  QuerySection->Type = NTOHS (QuerySection->Type);
-  QuerySection->Class = NTOHS (QuerySection->Class);
+  if (RemainingLength <= QueryNameLen + sizeof (DNS_QUERY_SECTION)) {
+    *Completed = FALSE;
+    return EFI_ABORTED;
+  } else {
+    RemainingLength -= (QueryNameLen + sizeof (DNS_QUERY_SECTION));
+  }
 
   //
-  // Get Answer name
+  // Get query section
   //
-  AnswerName = (CHAR8 *) QuerySection + sizeof (*QuerySection);
+  QuerySection = (DNS_QUERY_SECTION *) (QueryName + QueryNameLen);
+  QuerySection->Type = NTOHS (QuerySection->Type);
+  QuerySection->Class = NTOHS (QuerySection->Class);
 
   OldTpl = gBS->RaiseTPL (TPL_CALLBACK);
 
   //
   // Check DnsResponse Validity, if so, also get a valid NET_MAP_ITEM.
@@ -1339,14 +1370,30 @@ ParseDnsResponse (
     }
   }
 
   Status = EFI_NOT_FOUND;
 
+  //
+  // Get Answer name
+  //
+  AnswerName = (CHAR8 *) QuerySection + sizeof (*QuerySection);
+
   //
   // Processing AnswerSection.
   //
   while (AnswerSectionNum < DnsHeader->AnswersNum) {
+    //
+    // Check whether the remaining packet length is avaiable or not.
+    //
+    if (RemainingLength <= sizeof (UINT16) + sizeof (DNS_ANSWER_SECTION)) {
+      *Completed = FALSE;
+      Status = EFI_ABORTED;
+      goto ON_EXIT;
+    } else {
+      RemainingLength -= (sizeof (UINT16) + sizeof (DNS_ANSWER_SECTION));
+    }
+
     //
     // Answer name should be PTR, else EFI_UNSUPPORTED returned.
     //
     if ((*(UINT8 *) AnswerName & 0xC0) != 0xC0) {
       Status = EFI_UNSUPPORTED;
@@ -1360,10 +1407,21 @@ ParseDnsResponse (
     AnswerSection->Type = NTOHS (AnswerSection->Type);
     AnswerSection->Class = NTOHS (AnswerSection->Class);
     AnswerSection->Ttl = NTOHL (AnswerSection->Ttl);
     AnswerSection->DataLength = NTOHS (AnswerSection->DataLength);
 
+    //
+    // Check whether the remaining packet length is avaiable or not.
+    //
+    if (RemainingLength < AnswerSection->DataLength) {
+      *Completed = FALSE;
+      Status = EFI_ABORTED;
+      goto ON_EXIT;
+    } else {
+      RemainingLength -= AnswerSection->DataLength;
+    }
+
     //
     // Check whether it's the GeneralLookUp querying.
     //
     if (Instance->Service->IpVersion == IP_VERSION_4 && Dns4TokenEntry->GeneralLookUp) {
       Dns4RR = Dns4TokenEntry->Token->RspData.GLookupData->RRList;
@@ -1731,10 +1789,11 @@ DnsOnPacketReceived (
   )
 {
   DNS_INSTANCE              *Instance;
 
   UINT8                     *RcvString;
+  UINT32                    Len;
 
   BOOLEAN                   Completed;
 
   Instance  = (DNS_INSTANCE *) Context;
   NET_CHECK_SIGNATURE (Instance, DNS_INSTANCE_SIGNATURE);
@@ -1746,21 +1805,19 @@ DnsOnPacketReceived (
     goto ON_EXIT;
   }
 
   ASSERT (Packet != NULL);
 
-  if (Packet->TotalSize <= sizeof (DNS_HEADER)) {
-    goto ON_EXIT;
-  }
+  Len = Packet->TotalSize;
 
   RcvString = NetbufGetByte (Packet, 0, NULL);
   ASSERT (RcvString != NULL);
 
   //
   // Parse Dns Response
   //
-  ParseDnsResponse (Instance, RcvString, &Completed);
+  ParseDnsResponse (Instance, RcvString, Len, &Completed);
 
 ON_EXIT:
 
   if (Packet != NULL) {
     NetbufFree (Packet);
diff --git a/NetworkPkg/DnsDxe/DnsImpl.h b/NetworkPkg/DnsDxe/DnsImpl.h
index 90dc054903..45feca2160 100644
--- a/NetworkPkg/DnsDxe/DnsImpl.h
+++ b/NetworkPkg/DnsDxe/DnsImpl.h
@@ -581,20 +581,22 @@ IsValidDnsResponse (
 /**
   Parse Dns Response.
 
   @param  Instance              The DNS instance
   @param  RxString              Received buffer.
+  @param  Length                Received buffer length.
   @param  Completed             Flag to indicate that Dns response is valid.
 
   @retval EFI_SUCCESS           Parse Dns Response successfully.
   @retval Others                Failed to parse Dns Response.
 
 **/
 EFI_STATUS
 ParseDnsResponse (
   IN OUT DNS_INSTANCE              *Instance,
   IN     UINT8                     *RxString,
+  IN     UINT32                    Length,
      OUT BOOLEAN                   *Completed
   );
 
 /**
   Parse response packet.
-- 
2.17.1.windows.2