Re: [PATCH] MdeModulePkg/UdfDxe: Additional checks for ResolveSymlink()

[Leif Lindholm <leif.lindholm@linaro.org>]

Hi Hao Wu,

I have no comment about the code changes, but would it be possible to
split this up into three separate patches? They are three separate
changes, but as it stands, it is not _obvious_ that they do not have
interdependencies. Splitting them up would make that immediately
obvious. You already have the three commit messages :)

Best Regards,

Leif

On Fri, Oct 26, 2018 at 03:54:57PM +0800, Hao Wu wrote:
> REF:https://bugzilla.tianocore.org/show_bug.cgi?id=1279
> 
> The commit will add 3 types of checks for function ResolveSymlink():
> 
> A. Check for the value of 'Component Type' field within a Path Component
> 
> According to the ECMA-167 standard (3rd Edition - June 1997), Section
> 14.16.1.1, valid values are 1 to 5. All other values will be treated as a
> corrupted volume.
> 
> B. Check for the content pointed by 'File'
> 
> Since content within 'File' is the output data for ResolveSymlink().
> Checks is added to ensure the content in 'File' is valid. Otherwise,
> possible null pointer dereference issue will occur during the subsequent
> usage of the data returned by ResolveSymlink().
> 
> C. Check for possible memory double free/use after free case
> 
> For codes:
> 
>     if (CompareMem ((VOID *)&PreviousFile, (VOID *)Parent,
>                     sizeof (UDF_FILE_INFO)) != 0) {
>       CleanupFileInformation (&PreviousFile);
>     }
> 
>     CopyMem ((VOID *)&PreviousFile, (VOID *)File, sizeof (UDF_FILE_INFO));
> 
> If the contents in 'PreviousFile' and 'File' are the same, call to
> "CleanupFileInformation (&PreviousFile);" will free the buffers in 'File'
> as well. This will lead to potential memory double free/use after free
> issues.
> 
> Cc: Paulo Alcantara <paulo@paulo.ac>
> Cc: Paulo Alcantara <palcantara@suse.de>
> Cc: Ruiyu Ni <ruiyu.ni@intel.com>
> Cc: Star Zeng <star.zeng@intel.com>
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Hao Wu <hao.a.wu@intel.com>
> ---
>  .../Universal/Disk/UdfDxe/FileSystemOperations.c   | 30 ++++++++++++++++++++--
>  1 file changed, 28 insertions(+), 2 deletions(-)
> 
> diff --git a/MdeModulePkg/Universal/Disk/UdfDxe/FileSystemOperations.c b/MdeModulePkg/Universal/Disk/UdfDxe/FileSystemOperations.c
> index b9ebddfe62..a89e5ba9ff 100644
> --- a/MdeModulePkg/Universal/Disk/UdfDxe/FileSystemOperations.c
> +++ b/MdeModulePkg/Universal/Disk/UdfDxe/FileSystemOperations.c
> @@ -2145,6 +2145,8 @@ ResolveSymlink (
>    UINT8               CompressionId;
>    UDF_FILE_INFO       PreviousFile;
>  
> +  ZeroMem ((VOID *)File, sizeof (UDF_FILE_INFO));
> +
>    //
>    // Symlink files on UDF volumes do not contain so much data other than
>    // Path Components which resolves to real filenames, so it's OK to read in
> @@ -2257,6 +2259,13 @@ ResolveSymlink (
>        }
>        FileName[Index] = L'\0';
>        break;
> +    default:
> +      //
> +      // Accoring to the ECMA-167 standard (3rd Edition - June 1997), Section
> +      // 14.16.1.1, all other values are reserved.
> +      //
> +      Status = EFI_VOLUME_CORRUPTED;
> +      goto Error_Find_File;
>      }
>  
>      //
> @@ -2281,8 +2290,18 @@ ResolveSymlink (
>        break;
>      }
>  
> -    if (CompareMem ((VOID *)&PreviousFile, (VOID *)Parent,
> -                    sizeof (UDF_FILE_INFO)) != 0) {
> +    //
> +    // Check the content in the file info pointed by File.
> +    //
> +    if ((File->FileEntry == NULL) || (File->FileIdentifierDesc == NULL)) {
> +      Status = EFI_VOLUME_CORRUPTED;
> +      goto Error_Find_File;
> +    }
> +
> +    if ((CompareMem ((VOID *)&PreviousFile, (VOID *)Parent,
> +                    sizeof (UDF_FILE_INFO)) != 0) &&
> +        (CompareMem ((VOID *)&PreviousFile, (VOID *)File,
> +                    sizeof (UDF_FILE_INFO)) != 0)) {
>        CleanupFileInformation (&PreviousFile);
>      }
>  
> @@ -2294,6 +2313,13 @@ ResolveSymlink (
>    //
>    FreePool (ReadFileInfo.FileData);
>  
> +  //
> +  // Check the content in the resolved file info.
> +  //
> +  if ((File->FileEntry == NULL) || (File->FileIdentifierDesc == NULL)) {
> +    return EFI_VOLUME_CORRUPTED;
> +  }
> +
>    return EFI_SUCCESS;
>  
>  Error_Find_File:
> -- 
> 2.12.0.windows.1
> 
> _______________________________________________
> edk2-devel mailing list
> edk2-devel@lists.01.org
> https://lists.01.org/mailman/listinfo/edk2-devel