[PUBLIC edk2 PATCH v2 08/10] NetworkPkg/IScsiDxe: fix IScsiHexToBin() hex parsing

["Laszlo Ersek" <lersek@redhat.com>]

The IScsiHexToBin() function has the following parser issues:

(1) If the *subject sequence* in "HexStr" is empty, the function returns
    EFI_SUCCESS (with "BinLength" set to 0 on output). Such inputs should
    be rejected.

(2) The function mis-handles a "HexStr" that ends with a stray nibble. For
    example, if "HexStr" is "0xABC", the function decodes it to the bytes
    {0xAB, 0x0C}, sets "BinLength" to 2 on output, and returns
    EFI_SUCCESS. Such inputs should be rejected.

(3) If an invalid hex char is found in "HexStr", the function treats it as
    end-of-hex-string, and returns EFI_SUCCESS. Such inputs should be
    rejected.

All of the above cases are remotely triggerable, as shown in a subsequent
patch, which adds error checking to the IScsiHexToBin() call sites. While
the initiator is not immediately compromised, incorrectly parsing CHAP_R
from the target, in case of mutual authentication, is not great.

Extend the interface contract of IScsiHexToBin() with
EFI_INVALID_PARAMETER, for reporting issues (1) through (3), and implement
the new checks.

Cc: Jiaxin Wu <jiaxin.wu@intel.com>
Cc: Maciej Rabeda <maciej.rabeda@linux.intel.com>
Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
Cc: Siyuan Fu <siyuan.fu@intel.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=3356
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Maciej Rabeda <maciej.rabeda@linux.intel.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
 NetworkPkg/IScsiDxe/IScsiMisc.h |  1 +
 NetworkPkg/IScsiDxe/IScsiMisc.c | 12 ++++++++++--
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/NetworkPkg/IScsiDxe/IScsiMisc.h b/NetworkPkg/IScsiDxe/IScsiMisc.h
index 28cf408cd5c5..404a482e57f3 100644
--- a/NetworkPkg/IScsiDxe/IScsiMisc.h
+++ b/NetworkPkg/IScsiDxe/IScsiMisc.h
@@ -155,38 +155,39 @@ IScsiAsciiStrToIp (
 
 **/
 EFI_STATUS
 IScsiBinToHex (
   IN     UINT8  *BinBuffer,
   IN     UINT32 BinLength,
   IN OUT CHAR8  *HexStr,
   IN OUT UINT32 *HexLength
   );
 
 /**
   Convert the hexadecimal string into a binary encoded buffer.
 
   @param[in, out]  BinBuffer    The binary buffer.
   @param[in, out]  BinLength    Length of the binary buffer.
   @param[in]       HexStr       The hexadecimal string.
 
   @retval EFI_SUCCESS           The hexadecimal string is converted into a
                                 binary encoded buffer.
+  @retval EFI_INVALID_PARAMETER Invalid hex encoding found in HexStr.
   @retval EFI_BUFFER_TOO_SMALL  The binary buffer is too small to hold the
                                 converted data.
 **/
 EFI_STATUS
 IScsiHexToBin (
   IN OUT UINT8  *BinBuffer,
   IN OUT UINT32 *BinLength,
   IN     CHAR8  *HexStr
   );
 
 
 /**
   Convert the decimal-constant string or hex-constant string into a numerical value.
 
   @param[in] Str                    String in decimal or hex.
 
   @return The numerical value.
 
 **/
diff --git a/NetworkPkg/IScsiDxe/IScsiMisc.c b/NetworkPkg/IScsiDxe/IScsiMisc.c
index 014700e87a5f..f0f4992b07c7 100644
--- a/NetworkPkg/IScsiDxe/IScsiMisc.c
+++ b/NetworkPkg/IScsiDxe/IScsiMisc.c
@@ -360,72 +360,80 @@ IScsiBinToHex (
     HexStr[Index * 2 + 2] = IScsiHexString[BinBuffer[Index] >> 4];
     HexStr[Index * 2 + 3] = IScsiHexString[BinBuffer[Index] & 0xf];
   }
 
   HexStr[Index * 2 + 2] = '\0';
 
   return EFI_SUCCESS;
 }
 
 
 /**
   Convert the hexadecimal string into a binary encoded buffer.
 
   @param[in, out]  BinBuffer    The binary buffer.
   @param[in, out]  BinLength    Length of the binary buffer.
   @param[in]       HexStr       The hexadecimal string.
 
   @retval EFI_SUCCESS           The hexadecimal string is converted into a
                                 binary encoded buffer.
+  @retval EFI_INVALID_PARAMETER Invalid hex encoding found in HexStr.
   @retval EFI_BUFFER_TOO_SMALL  The binary buffer is too small to hold the
                                 converted data.
 **/
 EFI_STATUS
 IScsiHexToBin (
   IN OUT UINT8  *BinBuffer,
   IN OUT UINT32 *BinLength,
   IN     CHAR8  *HexStr
   )
 {
   UINTN   Index;
   UINTN   Length;
   UINT8   Digit;
   CHAR8   TemStr[2];
 
   ZeroMem (TemStr, sizeof (TemStr));
 
   //
   // Find out how many hex characters the string has.
   //
   if ((HexStr[0] == '0') && ((HexStr[1] == 'x') || (HexStr[1] == 'X'))) {
     HexStr += 2;
   }
 
   Length = AsciiStrLen (HexStr);
 
+  //
+  // Reject an empty hex string; reject a stray nibble.
+  //
+  if (Length == 0 || Length % 2 != 0) {
+    return EFI_INVALID_PARAMETER;
+  }
+
   for (Index = 0; Index < Length; Index ++) {
     TemStr[0] = HexStr[Index];
     Digit = (UINT8) AsciiStrHexToUint64 (TemStr);
     if (Digit == 0 && TemStr[0] != '0') {
       //
-      // Invalid Lun Char.
+      // Invalid Hex Char.
       //
-      break;
+      return EFI_INVALID_PARAMETER;
     }
     if ((Index & 1) == 0) {
       BinBuffer [Index/2] = Digit;
     } else {
       BinBuffer [Index/2] = (UINT8) ((BinBuffer [Index/2] << 4) + Digit);
     }
   }
 
   *BinLength = (UINT32) ((Index + 1)/2);
 
   return EFI_SUCCESS;
 }
 
 
 /**
   Convert the decimal-constant string or hex-constant string into a numerical value.
 
   @param[in] Str                    String in decimal or hex.
 
-- 
2.19.1.3.g30247aa5d201