Re: [edk2-platforms][PATCH v3 04/11] Ext4Pkg: Add inode number validity check

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

On Fri, Jan 27, 2023 at 9:29 AM Savva Mitrofanov <savvamtr@gmail.com> wrote:
>
> We need to validate inode number to prevent possible null-pointer
> dereference of directory parent in Ext4OpenDirent. Also checks that
> inode number valid across opened partition before we read it in
> Ext4ReadInode.
>
> 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/Ext4Dxe/Ext4Disk.h   | 13 ++++++++--
>  Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h    | 25 ++++++++++++++++++++
>  Features/Ext4Pkg/Ext4Dxe/BlockGroup.c |  5 ++++
>  Features/Ext4Pkg/Ext4Dxe/Directory.c  | 10 ++++++++
>  4 files changed, 51 insertions(+), 2 deletions(-)
>
> diff --git a/Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h b/Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h
> index d0a455d0e572..70cb6c3209dd 100644
> --- a/Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h
> +++ b/Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h
> @@ -484,8 +484,17 @@ typedef UINT64  EXT4_BLOCK_NR;
>  typedef UINT32  EXT2_BLOCK_NR;
>  typedef UINT32  EXT4_INO_NR;
>
> -// 2 is always the root inode number in ext4
> -#define EXT4_ROOT_INODE_NR  2
> +/* Special inode numbers */
> +#define EXT4_ROOT_INODE_NR         2
> +#define EXT4_USR_QUOTA_INODE_NR    3
> +#define EXT4_GRP_QUOTA_INODE_NR    4
> +#define EXT4_BOOT_LOADER_INODE_NR  5
> +#define EXT4_UNDEL_DIR_INODE_NR    6
> +#define EXT4_RESIZE_INODE_NR       7
> +#define EXT4_JOURNAL_INODE_NR      8
> +
> +/* First non-reserved inode for old ext4 filesystems */
> +#define EXT4_GOOD_OLD_FIRST_INODE_NR  11
>
>  #define EXT4_BLOCK_FILE_HOLE  0
>
> diff --git a/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h b/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h
> index f608def7c9eb..2e489ce4dd86 100644
> --- a/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h
> +++ b/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h
> @@ -287,6 +287,31 @@ Ext4GetBlockGroupDesc (
>    IN UINT32          BlockGroup
>    );
>
> +/**
> +   Retrieves the first usable non-reserved inode number from the superblock
> +   of the opened partition.
> +
> +   @param[in]  Partition      Pointer to the opened ext4 partition.
> +
> +   @return The first usable inode number (non-reserved).
> +**/
> +#define EXT4_FIRST_INODE_NR(Partition)                                         \
> +  ((Partition->SuperBlock.s_rev_level == EXT4_GOOD_OLD_REV) ?                  \
> +         EXT4_GOOD_OLD_FIRST_INODE_NR :                                        \
> +         Partition->SuperBlock.s_first_ino)
> +
> +/**
> +   Checks inode number validity across superblock of the opened partition.
> +
> +   @param[in]  Partition      Pointer to the opened ext4 partition.
> +
> +   @return TRUE if inode number is valid.
> +**/
> +#define EXT4_IS_VALID_INODE_NR(Partition, InodeNum)                            \
> +  (InodeNum == EXT4_ROOT_INODE_NR ||                                           \
> +        (InodeNum >= EXT4_FIRST_INODE_NR(Partition) &&                         \
> +         InodeNum <= Partition->SuperBlock.s_inodes_count))
> +
>  /**
>     Reads an inode from disk.
>
> diff --git a/Features/Ext4Pkg/Ext4Dxe/BlockGroup.c b/Features/Ext4Pkg/Ext4Dxe/BlockGroup.c
> index cba96cd95afc..f34cdc5dbad7 100644
> --- a/Features/Ext4Pkg/Ext4Dxe/BlockGroup.c
> +++ b/Features/Ext4Pkg/Ext4Dxe/BlockGroup.c
> @@ -50,6 +50,11 @@ Ext4ReadInode (
>    EXT4_BLOCK_NR          InodeTableStart;
>    EFI_STATUS             Status;
>
> +  if (!EXT4_IS_VALID_INODE_NR (Partition, InodeNum)) {
> +    DEBUG ((DEBUG_ERROR, "[ext4] Error reading inode: inode number %lu isn't valid\n", InodeNum));
> +    return EFI_VOLUME_CORRUPTED;
> +  }
> +

I don't know how to feel about this patch.
I do not understand why we need this here (and below). Given
Ext4OpenDirent, how is this deref'ing a NULL pointer without this
check?
Has this been handled by the UTF8 patches and your \0 patch?

-- 
Pedro