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

["Savva Mitrofanov" <savvamtr@gmail.com>]

Yes, I checked this out. Your UTF8 patches and latest patch
which redirects '..' folder to proper '/' with my directory entry '\0' patch solves the problem.
However, we need to perform inode number validation at least in Ext4ReadInode.
As we discussed, we can do this in a simplified way. These changes will be in v4

Thanks!

> On 27 Jan 2023, at 20:19, Pedro Falcato <pedro.falcato@gmail.com> wrote:
> 
> 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