[edk2-devel] [edk2-platforms][PATCH v3 05/11] Ext4Pkg: Fix shift out of bounds in Ext4OpenSuperblock

[Pedro Falcato]

On Fri, Jan 27, 2023 at 9:29 AM Savva Mitrofanov <savvamtr at gmail.com> wrote:
>
> Missing check for wrong s_log_block_size exponent leads to shift out of
> bounds. Limit block size to 2 MiB
>
> Cc: Marvin Häuser <mhaeuser at posteo.de>
> Cc: Pedro Falcato <pedro.falcato at gmail.com>
> Cc: Vitaly Cheptsov <vit9696 at protonmail.com>
> Fixes: d9ceedca6c8f ("Ext4Pkg: Add Ext4Dxe driver.")
> Signed-off-by: Savva Mitrofanov <savvamtr at gmail.com>
> ---
>  Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h    | 14 ++++++++++++++
>  Features/Ext4Pkg/Ext4Dxe/Superblock.c |  5 +++++
>  2 files changed, 19 insertions(+)
>
> diff --git a/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h b/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h
> index 2e489ce4dd86..a23323319a59 100644
> --- a/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h
> +++ b/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h
> @@ -40,6 +40,20 @@
>  #define EXT4_EFI_PATH_MAX    4096
>  #define EXT4_DRIVER_VERSION  0x0000
>
> +//
> +// The EXT4 Specification doesn't strictly limit block size and this value could be up to 2^31,
> +// but in practice it is limited by PAGE_SIZE due to performance significant impact.
> +// Many EXT4 implementations have size of block limited to PAGE_SIZE. In many cases it's limited
> +// to 4096, which is a commonly supported page size on most MMU-capable hardware, and up to 65536.
> +// So, to take a balance between compatibility and security measures, it is decided to use the
> +// value of 2MiB as the limit, which is equal to page size on new hardware.
Nit: s/page size/large page size/
I can change this for you when pushing, no need for a v4 on this one.
> +// As for supporting big block sizes, EXT4 has a RO_COMPAT_FEATURE called BIGALLOC, which changes
> +// EXT4 to use clustered allocation, so that each bit in the ext4 block allocation bitmap addresses
> +// a power of two number of blocks. So it would be wiser to implement and use this feature
> +// if there is such a need instead of big block size.
> +//
> +#define EXT4_LOG_BLOCK_SIZE_MAX  11
> +
>  /**
>     Opens an ext4 partition and installs the Simple File System protocol.
>
> diff --git a/Features/Ext4Pkg/Ext4Dxe/Superblock.c b/Features/Ext4Pkg/Ext4Dxe/Superblock.c
> index be3527e4d618..3f56de93c105 100644
> --- a/Features/Ext4Pkg/Ext4Dxe/Superblock.c
> +++ b/Features/Ext4Pkg/Ext4Dxe/Superblock.c
> @@ -248,6 +248,11 @@ Ext4OpenSuperblock (
>      return EFI_VOLUME_CORRUPTED;
>    }
>
> +  if (Sb->s_log_block_size > EXT4_LOG_BLOCK_SIZE_MAX) {
> +    DEBUG ((DEBUG_ERROR, "[ext4] SuperBlock s_log_block_size %lu is too big\n", Sb->s_log_block_size));
> +    return EFI_UNSUPPORTED;
> +  }
> +
>    Partition->BlockSize = (UINT32)LShiftU64 (1024, Sb->s_log_block_size);
>
>    // The size of a block group can also be calculated as 8 * Partition->BlockSize
> --
> 2.39.0
>

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

-- 
Pedro


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