Re: [edk2-platforms][PATCH v4 06/12] Ext4Pkg: Corrects integer overflow check logic in DiskUtil

["Marvin Häuser" <mhaeuser@posteo.de>]

Reviewed-by: Marvin Häuser <mhaeuser@posteo.de>

> On 2. Feb 2023, at 11:21, Savva Mitrofanov <savvamtr@gmail.com> wrote:
> 
> Corrects multiplication overflow check code and adds additional check
> for emptiness of number of blocks and block number
> 
> 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 | 18 ++++++++++++++----
> Features/Ext4Pkg/Ext4Dxe/Extents.c  | 15 ++++++++++++---
> 3 files changed, 27 insertions(+), 8 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
> -  
> +
>   #
>   # Required for stack protector support
>   #
> diff --git a/Features/Ext4Pkg/Ext4Dxe/DiskUtil.c b/Features/Ext4Pkg/Ext4Dxe/DiskUtil.c
> index 32da35f7d9f5..5df9ce5bafcf 100644
> --- a/Features/Ext4Pkg/Ext4Dxe/DiskUtil.c
> +++ b/Features/Ext4Pkg/Ext4Dxe/DiskUtil.c
> @@ -54,17 +54,20 @@ Ext4ReadBlocks (
>   UINT64  Offset;
>   UINTN   Length;
> 
> +  ASSERT (NumberBlocks != 0);
> +  ASSERT (BlockNumber != EXT4_BLOCK_FILE_HOLE);
> +
>   Offset = MultU64x32 (BlockNumber, Partition->BlockSize);
>   Length = NumberBlocks * Partition->BlockSize;
> 
>   // 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 (DivU64x64Remainder (Offset, BlockNumber, NULL) != Partition->BlockSize) {
>     return EFI_INVALID_PARAMETER;
>   }
> 
> -  if (Length > (UINTN)-1/Partition->BlockSize) {
> +  if (Length / NumberBlocks != Partition->BlockSize) {
>     return EFI_INVALID_PARAMETER;
>   }
> 
> @@ -92,14 +95,21 @@ Ext4AllocAndReadBlocks (
>   VOID   *Buf;
>   UINTN  Length;
> 
> +  // Check that number of blocks isn't empty, because
> +  // this is incorrect condition for opened partition,
> +  // so we just early-exit
> +  if ((NumberBlocks == 0) || (BlockNumber == EXT4_BLOCK_FILE_HOLE)) {
> +    return NULL;
> +  }
> +
>   Length = NumberBlocks * Partition->BlockSize;
> 
> -  if (Length > (UINTN)-1/Partition->BlockSize) {
> +  // Check for integer overflow
> +  if (Length / NumberBlocks != Partition->BlockSize) {
>     return NULL;
>   }
> 
>   Buf = AllocatePool (Length);
> -
>   if (Buf == NULL) {
>     return NULL;
>   }
> diff --git a/Features/Ext4Pkg/Ext4Dxe/Extents.c b/Features/Ext4Pkg/Ext4Dxe/Extents.c
> index e1001d0a4292..99cb0f204fc2 100644
> --- a/Features/Ext4Pkg/Ext4Dxe/Extents.c
> +++ b/Features/Ext4Pkg/Ext4Dxe/Extents.c
> @@ -237,6 +237,7 @@ Ext4GetExtent (
>   EXT4_EXTENT_HEADER  *ExtHeader;
>   EXT4_EXTENT_INDEX   *Index;
>   EFI_STATUS          Status;
> +  EXT4_BLOCK_NR       BlockNumber;
> 
>   Inode  = File->Inode;
>   Ext    = NULL;
> @@ -288,7 +289,16 @@ Ext4GetExtent (
>     // Therefore, we can use binary search, and it's actually the standard for doing so
>     // (see FreeBSD).
> 
> -    Index = Ext4BinsearchExtentIndex (ExtHeader, LogicalBlock);
> +    Index       = Ext4BinsearchExtentIndex (ExtHeader, LogicalBlock);
> +    BlockNumber = Ext4ExtentIdxLeafBlock (Index);
> +
> +    // Check that block isn't file hole
> +    if (BlockNumber == EXT4_BLOCK_FILE_HOLE) {
> +      if (Buffer != NULL) {
> +        FreePool (Buffer);
> +      }
> +      return EFI_NO_MAPPING;
> +    }
> 
>     if (Buffer == NULL) {
>       Buffer = AllocatePool (Partition->BlockSize);
> @@ -298,8 +308,7 @@ Ext4GetExtent (
>     }
> 
>     // Read the leaf block onto the previously-allocated buffer.
> -
> -    Status = Ext4ReadBlocks (Partition, Buffer, 1, Ext4ExtentIdxLeafBlock (Index));
> +    Status = Ext4ReadBlocks (Partition, Buffer, 1, BlockNumber);
>     if (EFI_ERROR (Status)) {
>       FreePool (Buffer);
>       return Status;
> -- 
> 2.39.1
>