Re: [edk2-platforms][PATCH v3 06/11] Ext4Pkg: Corrects integer overflow check logic in DiskUtil

["Pedro Falcato" <pedro.falcato@gmail.com>]

On Fri, Jan 27, 2023 at 9:29 AM Savva Mitrofanov <savvamtr@gmail.com> wrote:
>
> Corrects multiplication overflow check code
>
> Cc: Marvin Häuser <mhaeuser@posteo.de>
> Cc: Pedro Falcato <pedro.falcato@gmail.com>
> Cc: Vitaly Cheptsov <vit9696@protonmail.com>
> Fixes: d9ceedca6c8f ("Ext4Pkg: Add Ext4Dxe driver.")
> Signed-off-by: Savva Mitrofanov <savvamtr@gmail.com>
> ---
>  Features/Ext4Pkg/Ext4Pkg.dsc        | 2 +-
>  Features/Ext4Pkg/Ext4Dxe/DiskUtil.c | 8 ++++----
>  2 files changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/Features/Ext4Pkg/Ext4Pkg.dsc b/Features/Ext4Pkg/Ext4Pkg.dsc
> index 59bc327ebf6e..621c63eaf92d 100644
> --- a/Features/Ext4Pkg/Ext4Pkg.dsc
> +++ b/Features/Ext4Pkg/Ext4Pkg.dsc
> @@ -46,7 +46,7 @@
>    DevicePathLib|MdePkg/Library/UefiDevicePathLib/UefiDevicePathLib.inf
>    OrderedCollectionLib|MdePkg/Library/BaseOrderedCollectionRedBlackTreeLib/BaseOrderedCollectionRedBlackTreeLib.inf
>    BaseUcs2Utf8Lib|RedfishPkg/Library/BaseUcs2Utf8Lib/BaseUcs2Utf8Lib.inf
> -
> +
Why this whitespace change?
>    #
>    # Required for stack protector support
>    #
> diff --git a/Features/Ext4Pkg/Ext4Dxe/DiskUtil.c b/Features/Ext4Pkg/Ext4Dxe/DiskUtil.c
> index 32da35f7d9f5..c4af956da926 100644
> --- a/Features/Ext4Pkg/Ext4Dxe/DiskUtil.c
> +++ b/Features/Ext4Pkg/Ext4Dxe/DiskUtil.c
> @@ -60,11 +60,11 @@ Ext4ReadBlocks (
>    // Check for overflow on the block -> byte conversions.
>    // Partition->BlockSize is never 0, so we don't need to check for that.
>
> -  if (Offset > DivU64x32 ((UINT64)-1, Partition->BlockSize)) {
> +  if ((NumberBlocks != 0) && (DivU64x64Remainder (Offset, BlockNumber, NULL) != Partition->BlockSize)) {
>      return EFI_INVALID_PARAMETER;
>    }
>
> -  if (Length > (UINTN)-1/Partition->BlockSize) {
> +  if ((NumberBlocks != 0) && (Length / NumberBlocks != Partition->BlockSize)) {
>      return EFI_INVALID_PARAMETER;
>    }
>
> @@ -94,12 +94,12 @@ Ext4AllocAndReadBlocks (
>
>    Length = NumberBlocks * Partition->BlockSize;
>
> -  if (Length > (UINTN)-1/Partition->BlockSize) {
> +  // Check for integer overflow
> +  if ((NumberBlocks != 0) && (Length / NumberBlocks != Partition->BlockSize)) {
>      return NULL;
>    }
>
>    Buf = AllocatePool (Length);
> -
>    if (Buf == NULL) {
>      return NULL;
>    }
> --
> 2.39.0
>

I don't really like open coding this, but it does fix my buggy checks.

In the interest of not adding a new overengineered safe int library,

Reviewed-by: Pedro Falcato <pedro.falcato@gmail.com>


-- 
Pedro