Re: [PATCH V2 3/3] DuetPkg FsVariable: Update GetNextVariableName to follow UEFI 2.7

["Zeng, Star" <star.zeng@intel.com>]

Ray,

It is to pass the check quickly and avoid scanning all the chars in VariableName by StrnLenS for normal boot without invalid cases.
I did experiments in the code of GetNextVariableName with below debug code for normal boot on NT32 and my real platforms, all the cases will go into the branch "xxx 2".
  if (((VariableName[MaxLen - 1] != 0))) {
    DEBUG ((DEBUG_INFO, "xxx 1\n"));
  } else {
    DEBUG ((DEBUG_INFO, "xxx 2\n"));
  }


Thanks,
Star
-----Original Message-----
From: Ni, Ruiyu 
Sent: Friday, June 23, 2017 4:20 PM
To: Zeng, Star <star.zeng@intel.com>; edk2-devel@lists.01.org
Cc: Gao, Liming <liming.gao@intel.com>
Subject: RE: [PATCH V2 3/3] DuetPkg FsVariable: Update GetNextVariableName to follow UEFI 2.7

Star,
What's the benefit of this check "VariableName[MaxLen - 1] != 0"?
I think this check "StrnLenS (VariableName, MaxLen) == MaxLen" should be enough.

Thanks/Ray

> -----Original Message-----
> From: Zeng, Star
> Sent: Friday, June 23, 2017 4:08 PM
> To: edk2-devel@lists.01.org
> Cc: Zeng, Star <star.zeng@intel.com>; Gao, Liming <liming.gao@intel.com>;
> Ni, Ruiyu <ruiyu.ni@intel.com>
> Subject: [PATCH V2 3/3] DuetPkg FsVariable: Update GetNextVariableName
> to follow UEFI 2.7
> 
> "The size must be large enough to fit input string supplied in
> VariableName buffer" is added in the description for VariableNameSize.
> And two cases of EFI_INVALID_PARAMETER are added.
> 1. The input values of VariableName and VendorGuid are not a name and
>    GUID of an existing variable.
> 2. Null-terminator is not found in the first VariableNameSize bytes of
>    the input VariableName buffer.
> 
> This patch is to update code to follow them.
> 
> Cc: Liming Gao <liming.gao@intel.com>
> Cc: Ruiyu Ni <ruiyu.ni@intel.com>
> Contributed-under: TianoCore Contribution Agreement 1.0
> Signed-off-by: Star Zeng <star.zeng@intel.com>
> ---
>  DuetPkg/FSVariable/FSVariable.c | 21 ++++++++++++++++++++-
>  1 file changed, 20 insertions(+), 1 deletion(-)
> 
> diff --git a/DuetPkg/FSVariable/FSVariable.c
> b/DuetPkg/FSVariable/FSVariable.c
> index 34b79305c871..6069cfa8fb98 100644
> --- a/DuetPkg/FSVariable/FSVariable.c
> +++ b/DuetPkg/FSVariable/FSVariable.c
> @@ -6,7 +6,7 @@ disk. They can be changed by user. BIOS is not able to
> protoect those.
>  Duet trusts all meta data from disk. If variable code, variable metadata and
> variable
>  data is modified in inproper way, the behavior is undefined.
> 
> -Copyright (c) 2006 - 2016, Intel Corporation. All rights reserved.<BR>
> +Copyright (c) 2006 - 2017, Intel Corporation. All rights reserved.<BR>
>  This program and the accompanying materials
>  are licensed and made available under the terms and conditions of the BSD
> License
>  which accompanies this distribution.  The full text of the license may be
> found at
> @@ -1400,14 +1400,33 @@ Returns:
>    VARIABLE_POINTER_TRACK  Variable;
>    UINTN                   VarNameSize;
>    EFI_STATUS              Status;
> +  UINTN                   MaxLen;
> 
>    if (VariableNameSize == NULL || VariableName == NULL || VendorGuid ==
> NULL) {
>      return EFI_INVALID_PARAMETER;
>    }
> 
> +  //
> +  // Calculate the possible maximum length of name string, including the Null
> terminator.
> +  //
> +  MaxLen = *VariableNameSize / sizeof (CHAR16);
> +  if ((MaxLen == 0) ||
> +      ((VariableName[MaxLen - 1] != 0) && (StrnLenS (VariableName, MaxLen)
> == MaxLen))) {
> +    //
> +    // Null-terminator is not found in the first VariableNameSize bytes of the
> input VariableName buffer.
> +    //
> +    return EFI_INVALID_PARAMETER;
> +  }
> +
>    Status = FindVariable (VariableName, VendorGuid, &Variable);
> 
>    if (Variable.CurrPtr == NULL || EFI_ERROR (Status)) {
> +    if (VariableName[0] != 0) {
> +      //
> +      // The input values of VariableName and VendorGuid are not a name
> and GUID of an existing variable.
> +      //
> +      Status = EFI_INVALID_PARAMETER;
> +    }
>      return Status;
>    }
> 
> --
> 2.7.0.windows.1