Re: [PATCH 7/9] SecurityPkg/DxeImageVerificationLib: tighten default result of IsForbiddenByDbx()(CVE-2019-14575)

["Yao, Jiewen" <jiewen.yao@intel.com>]

Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>

> -----Original Message-----
> From: Wang, Jian J <jian.j.wang@intel.com>
> Sent: Thursday, February 6, 2020 10:20 PM
> To: devel@edk2.groups.io
> Cc: Yao, Jiewen <jiewen.yao@intel.com>; Zhang, Chao B
> <chao.b.zhang@intel.com>; Laszlo Ersek <lersek@redhat.com>
> Subject: [PATCH 7/9] SecurityPkg/DxeImageVerificationLib: tighten default
> result of IsForbiddenByDbx()(CVE-2019-14575)
> 
> REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1608
> 
> All intermediate results inside this function will be checked and
> returned immediately upon any failure or error, like out-of-resource,
> hash calculation error or certificate retrieval failure.
> 
> Cc: Jiewen Yao <jiewen.yao@intel.com>
> Cc: Chao Zhang <chao.b.zhang@intel.com>
> Signed-off-by: Jian J Wang <jian.j.wang@intel.com>
> Signed-off-by: Laszlo Ersek <lersek@redhat.com>
> ---
>  .../DxeImageVerificationLib/DxeImageVerificationLib.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git
> a/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c
> b/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c
> index a5dfee0f8e..2236ce98ce 100644
> --- a/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c
> +++ b/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c
> @@ -1240,7 +1240,7 @@ IsForbiddenByDbx (
>    //
> 
>    // Variable Initialization
> 
>    //
> 
> -  IsForbidden       = FALSE;
> 
> +  IsForbidden       = TRUE;
> 
>    Data              = NULL;
> 
>    CertList          = NULL;
> 
>    CertData          = NULL;
> 
> @@ -1257,7 +1257,14 @@ IsForbiddenByDbx (
>    //
> 
>    DataSize = 0;
> 
>    Status   = gRT->GetVariable (EFI_IMAGE_SECURITY_DATABASE1,
> &gEfiImageSecurityDatabaseGuid, NULL, &DataSize, NULL);
> 
> +  ASSERT (EFI_ERROR (Status));
> 
>    if (Status != EFI_BUFFER_TOO_SMALL) {
> 
> +    if (Status == EFI_NOT_FOUND) {
> 
> +      //
> 
> +      // Evidently not in dbx if the database doesn't exist.
> 
> +      //
> 
> +      IsForbidden = FALSE;
> 
> +    }
> 
>      return IsForbidden;
> 
>    }
> 
>    Data = (UINT8 *) AllocateZeroPool (DataSize);
> 
> @@ -1366,6 +1373,8 @@ IsForbiddenByDbx (
> 
> 
>    }
> 
> 
> 
> +  IsForbidden = FALSE;
> 
> +
> 
>  Done:
> 
>    if (Data != NULL) {
> 
>      FreePool (Data);
> 
> --
> 2.24.0.windows.2