Re: [edk2-devel] [PATCH 3/3] SecurityPkg/DxeImageVerificationLib: catch alignment overflow (CVE-2019-14562)

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

Hi Laszlo,

On 9/1/20 11:12 AM, Laszlo Ersek wrote:
> The DxeImageVerificationHandler() function currently checks whether
> "SecDataDir" has enough room for "WinCertificate->dwLength". However, for
> advancing "OffSet", "WinCertificate->dwLength" is aligned to the next
> multiple of 8. If "WinCertificate->dwLength" is large enough, the
> alignment will return 0, and "OffSet" will be stuck at the same value.
> 
> Check whether "SecDataDir" has room left for both
> "WinCertificate->dwLength" and the alignment.
> 
> Cc: Jian J Wang <jian.j.wang@intel.com>
> Cc: Jiewen Yao <jiewen.yao@intel.com>
> Cc: Min Xu <min.m.xu@intel.com>
> Cc: Wenyi Xie <xiewenyi2@huawei.com>
> Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=2215
> Signed-off-by: Laszlo Ersek <lersek@redhat.com>
> ---
>  SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c b/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c
> index 100739eb3eb6..11154b6cc58a 100644
> --- a/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c
> +++ b/SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c
> @@ -1860,7 +1860,9 @@ DxeImageVerificationHandler (
>        break;
>      }
>      WinCertificate = (WIN_CERTIFICATE *) (mImageBase + OffSet);
> -    if (SecDataDirLeft < WinCertificate->dwLength) {
> +    if (SecDataDirLeft < WinCertificate->dwLength ||
> +        (SecDataDirLeft - WinCertificate->dwLength <
> +         ALIGN_SIZE (WinCertificate->dwLength))) {

I dare to ask (probably again, I remember some similar boundary check
style question once), why not as (which is simpler for me to review):

       if (SecDataDirLeft < WinCertificate->dwLength + ALIGN_SIZE
(WinCertificate->dwLength)) {

At any rate, for this patch:
Reviewed-by: Philippe Mathieu-Daude <philmd@redhat.com>

>        break;
>      }
>  
>