Re: [edk2-platforms][PATCH v2 1/1] Ext4Pkg: Code correctness and security improvements

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

Hi Marvin,

Thanks for comments! 

> On 20 Jul 2022, at 23:54, Marvin Häuser <mhaeuser@posteo.de> wrote:
> 
> On 20. Jul 2022, at 07:36, Savva Mitrofanov <savvamtr@gmail.com> wrote:
>> 
>> This changes tends to improve security of code sections by fixing
>> integer overflows, missing aligment checks, unsafe casts, also
>> simplified some routines, fixed compiler warnings and corrected some
>> code mistakes.
>> 
>> - Set HoleLen to UINT64 to perform safe cast to UINTN in ternary
>> operator at WasRead assignment.
> 
> In my opinion, just "to prevent truncation".
> 
>> - Replace EXT4_BLOCK_NR with 32-bit EXT2_BLOCK_NR in BlockMap, because
>> we consider BlockMap is 32-bit fs ext2/3 feature.
>> - Replace UNREACHABLE with ASSERT (FALSE) in case of new checksum
>> algorithms, due to it is an invariant violation rather than unreachable
>> path.
>> - Solve compiler warnings. Init all fields in gExt4BindingProtocol.
>> Fix comparison of integer expressions of different signedness.
>> - Field name_len has type CHAR8, while filename limit is 255
>> (EXT4_NAME_MAX), so because structure EXT4_DIR_ENTRY would be
>> unchangeable in future, we could drop this check without any
>> assertions
>> - Simplify Ext4RemoveDentry logic by using IsNodeInList
>> - Fix possible int overflow in Ext4ExtentsMapKeyCompare
>> - Return bad block type in Ext4GetBlockpath
>> - Adds 4-byte aligned check for superblock group descriptor size field
>> 
>> Cc: Marvin Häuser <mhaeuser@posteo.de>
>> Cc: Pedro Falcato <pedro.falcato@gmail.com>
>> Cc: Vitaly Cheptsov <vit9696@protonmail.com>
>> Signed-off-by: Savva Mitrofanov <savvamtr@gmail.com>
>> ---
>> Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h   |  3 +-
>> Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h    |  2 +-
>> Features/Ext4Pkg/Ext4Dxe/BlockMap.c   | 18 ++++++++----
>> Features/Ext4Pkg/Ext4Dxe/Directory.c  | 29 ++------------------
>> Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.c    | 10 ++++---
>> Features/Ext4Pkg/Ext4Dxe/Extents.c    |  5 ++--
>> Features/Ext4Pkg/Ext4Dxe/Inode.c      |  8 +++---
>> Features/Ext4Pkg/Ext4Dxe/Superblock.c | 13 +++++----
>> 8 files changed, 38 insertions(+), 50 deletions(-)
>> 
>> diff --git a/Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h b/Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h
>> index a55cd2fa68ad..7a19d2f79d53 100644
>> --- a/Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h
>> +++ b/Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h
>> @@ -338,7 +338,7 @@ STATIC_ASSERT (
>> #define EXT4_TIND_BLOCK  14
>> #define EXT4_NR_BLOCKS   15
>> 
>> -#define EXT4_GOOD_OLD_INODE_SIZE  128
>> +#define EXT4_GOOD_OLD_INODE_SIZE  128U
>> 
>> typedef struct _Ext4_I_OSD2_Linux {
>>  UINT16    l_i_blocks_high;
>> @@ -463,6 +463,7 @@ typedef struct {
>> #define EXT4_EXTENT_MAX_INITIALIZED  (1 << 15)
>> 
>> typedef UINT64  EXT4_BLOCK_NR;
>> +typedef UINT32  EXT2_BLOCK_NR;
>> typedef UINT32  EXT4_INO_NR;
>> 
>> // 2 is always the root inode number in ext4
>> diff --git a/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h b/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h
>> index b1508482b0a7..b446488b2112 100644
>> --- a/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h
>> +++ b/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h
>> @@ -1165,7 +1165,7 @@ EFI_STATUS
>> Ext4GetBlocks (
>>  IN  EXT4_PARTITION  *Partition,
>>  IN  EXT4_FILE       *File,
>> -  IN  EXT4_BLOCK_NR   LogicalBlock,
>> +  IN  EXT2_BLOCK_NR   LogicalBlock,
> 
> This looks awkward, using an "EXT2" type in an "Ext4" function. Maybe just use UINT32?

The idea to use such type naming belongs to Pedro, and in recent discussions he insisted on this, due EXT2_BLOCK_NR is more explicit than using UINT32 directly.
So, I'll keep it in v3.

> 
>>  OUT EXT4_EXTENT     *Extent
>>  );
>> 
>> diff --git a/Features/Ext4Pkg/Ext4Dxe/BlockMap.c b/Features/Ext4Pkg/Ext4Dxe/BlockMap.c
>> index 1a06ac9fbf86..2bc629fe9d38 100644
>> --- a/Features/Ext4Pkg/Ext4Dxe/BlockMap.c
>> +++ b/Features/Ext4Pkg/Ext4Dxe/BlockMap.c
>> @@ -70,7 +70,7 @@ UINTN
>> Ext4GetBlockPath (
>>  IN  CONST EXT4_PARTITION  *Partition,
>>  IN  UINT32                LogicalBlock,
>> -  OUT EXT4_BLOCK_NR         BlockPath[EXT4_MAX_BLOCK_PATH]
>> +  OUT EXT2_BLOCK_NR         BlockPath[EXT4_MAX_BLOCK_PATH]
>>  )
>> {
>>  // The logic behind the block map is very much like a page table
>> @@ -123,7 +123,7 @@ Ext4GetBlockPath (
>>      break;
>>    default:
>>      // EXT4_TYPE_BAD_BLOCK
>> -      return -1;
>> +      break;
>>  }
>> 
>>  return Type + 1;
>> @@ -213,12 +213,12 @@ EFI_STATUS
>> Ext4GetBlocks (
>>  IN  EXT4_PARTITION  *Partition,
>>  IN  EXT4_FILE       *File,
>> -  IN  EXT4_BLOCK_NR   LogicalBlock,
>> +  IN  EXT2_BLOCK_NR   LogicalBlock,
>>  OUT EXT4_EXTENT     *Extent
>>  )
>> {
>>  EXT4_INODE     *Inode;
>> -  EXT4_BLOCK_NR  BlockPath[EXT4_MAX_BLOCK_PATH];
>> +  EXT2_BLOCK_NR  BlockPath[EXT4_MAX_BLOCK_PATH];
>>  UINTN          BlockPathLength;
>>  UINTN          Index;
>>  UINT32         *Buffer;
>> @@ -230,7 +230,7 @@ Ext4GetBlocks (
>> 
>>  BlockPathLength = Ext4GetBlockPath (Partition, LogicalBlock, BlockPath);
>> 
>> -  if (BlockPathLength == (UINTN)-1) {
>> +  if (BlockPathLength - 1 == EXT4_TYPE_BAD_BLOCK) {
>>    // Bad logical block (out of range)
>>    return EFI_NO_MAPPING;
>>  }
>> @@ -272,7 +272,13 @@ Ext4GetBlocks (
>>    }
>>  }
>> 
>> -  Ext4GetExtentInBlockMap (Buffer, Partition->BlockSize / sizeof (UINT32), BlockPath[BlockPathLength - 1], Extent);
>> +  Ext4GetExtentInBlockMap (
>> +    Buffer,
>> +    Partition->BlockSize / sizeof (UINT32),
>> +    BlockPath[BlockPathLength - 1],
>> +    Extent
>> +    );
>> +
>>  FreePool (Buffer);
>> 
>>  return EFI_SUCCESS;
>> diff --git a/Features/Ext4Pkg/Ext4Dxe/Directory.c b/Features/Ext4Pkg/Ext4Dxe/Directory.c
>> index 682f66ad5525..4441e6d192b6 100644
>> --- a/Features/Ext4Pkg/Ext4Dxe/Directory.c
>> +++ b/Features/Ext4Pkg/Ext4Dxe/Directory.c
>> @@ -74,7 +74,7 @@ Ext4ValidDirent (
>>  }
>> 
>>  // Dirent sizes need to be 4 byte aligned
>> -  if (Dirent->rec_len % 4) {
>> +  if ((Dirent->rec_len % 4) != 0) {
>>    return FALSE;
>>  }
>> 
>> @@ -160,17 +160,6 @@ Ext4RetrieveDirent (
>>        return EFI_VOLUME_CORRUPTED;
>>      }
>> 
>> -      // Ignore names bigger than our limit.
>> -
>> -      /* Note: I think having a limit is sane because:
>> -        1) It's nicer to work with.
>> -        2) Linux and a number of BSDs also have a filename limit of 255.
>> -      */
>> -      if (Entry->name_len > EXT4_NAME_MAX) {
>> -        BlockOffset += Entry->rec_len;
>> -        continue;
>> -      }
>> -
>>      // Unused entry
>>      if (Entry->inode == 0) {
>>        BlockOffset += Entry->rec_len;
>> @@ -548,20 +537,8 @@ Ext4RemoveDentry (
>>  IN OUT EXT4_DENTRY  *ToBeRemoved
>>  )
>> {
>> -  EXT4_DENTRY  *D;
>> -  LIST_ENTRY   *Entry;
>> -  LIST_ENTRY   *NextEntry;
>> -
>> -  BASE_LIST_FOR_EACH_SAFE (Entry, NextEntry, &Parent->Children) {
>> -    D = EXT4_DENTRY_FROM_DENTRY_LIST (Entry);
>> -
>> -    if (D == ToBeRemoved) {
>> -      RemoveEntryList (Entry);
>> -      return;
>> -    }
>> -  }
>> -
>> -  DEBUG ((DEBUG_ERROR, "[ext4] Ext4RemoveDentry did not find the asked-for dentry\n"));
>> +  ASSERT (IsNodeInList (&ToBeRemoved->ListNode, &Parent->Children));
>> +  RemoveEntryList (&ToBeRemoved->ListNode);
>> }
>> 
>> /**
>> diff --git a/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.c b/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.c
>> index 43b9340d3956..2a4f5a7bd0ef 100644
>> --- a/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.c
>> +++ b/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.c
>> @@ -260,10 +260,12 @@ Ext4Stop (
>> 
>> EFI_DRIVER_BINDING_PROTOCOL  gExt4BindingProtocol =
>> {
>> -  Ext4IsBindingSupported,
>> -  Ext4Bind,
>> -  Ext4Stop,
>> -  EXT4_DRIVER_VERSION
>> +  .Supported           = Ext4IsBindingSupported,
>> +  .Start               = Ext4Bind,
>> +  .Stop                = Ext4Stop,
>> +  .Version             = EXT4_DRIVER_VERSION,
>> +  .ImageHandle         = NULL,
>> +  .DriverBindingHandle = NULL
>> };
>> 
>> /**
>> diff --git a/Features/Ext4Pkg/Ext4Dxe/Extents.c b/Features/Ext4Pkg/Ext4Dxe/Extents.c
>> index c3874df71751..d9ff69f21c14 100644
>> --- a/Features/Ext4Pkg/Ext4Dxe/Extents.c
>> +++ b/Features/Ext4Pkg/Ext4Dxe/Extents.c
>> @@ -259,7 +259,8 @@ Ext4GetExtent (
>> 
>>  if (!(Inode->i_flags & EXT4_EXTENTS_FL)) {
>>    // If this is an older ext2/ext3 filesystem, emulate Ext4GetExtent using the block map
>> -    Status = Ext4GetBlocks (Partition, File, LogicalBlock, Extent);
>> +    // We cast LogicalBlock to UINT32, considering ext2/3 are 32-bit
> 
> The comment is misleading, because this is safe for EXT4 as well.

As we discussed, in 64-bit fs we have 2^64 maximum blocks. But if we dig deeper, we find that files which are not using extents, but using blockmaps must be placed within the first 2^32 blocks of the filesystem by the spec, so in this case it is safe, and the comment about the 32-bit nature of ext2/3 is improper here.
We should rewrite it like this:
    // If this is an older ext2/ext3 filesystem, emulate Ext4GetExtent using the block map
    // By specification files using block maps must be placed within the first 2^32 blocks
    // of a filesystem, so we can safely cast LogicalBlock to uint32

> 
>> +    Status = Ext4GetBlocks (Partition, File, (UINT32)LogicalBlock, Extent);
>> 
>>    if (!EFI_ERROR (Status)) {
>>      Ext4CacheExtents (File, Extent, 1);
>> @@ -420,7 +421,7 @@ Ext4ExtentsMapKeyCompare (
>>  Extent = UserStruct;
>>  Block  = (UINT32)(UINTN)StandaloneKey;
>> 
>> -  if ((Block >= Extent->ee_block) && (Block < Extent->ee_block + Ext4GetExtentLength (Extent))) {
>> +  if ((Block >= Extent->ee_block) && (Block - Extent->ee_block < Ext4GetExtentLength (Extent))) {
>>    return 0;
>>  }
>> 
>> diff --git a/Features/Ext4Pkg/Ext4Dxe/Inode.c b/Features/Ext4Pkg/Ext4Dxe/Inode.c
>> index 831f5946e870..4860cf576377 100644
>> --- a/Features/Ext4Pkg/Ext4Dxe/Inode.c
>> +++ b/Features/Ext4Pkg/Ext4Dxe/Inode.c
>> @@ -100,7 +100,7 @@ Ext4Read (
>>  EFI_STATUS   Status;
>>  BOOLEAN      HasBackingExtent;
>>  UINT32       HoleOff;
>> -  UINTN        HoleLen;
>> +  UINT64       HoleLen;
>>  UINT64       ExtentStartBytes;
>>  UINT64       ExtentLengthBytes;
>>  UINT64       ExtentLogicalBytes;
>> @@ -155,10 +155,10 @@ Ext4Read (
>>        HoleLen = (Ext4GetExtentLength (&Extent) * Partition->BlockSize) - HoleOff;
>>      }
>> 
>> -      WasRead = HoleLen > RemainingRead ? RemainingRead : HoleLen;
>> +      WasRead = HoleLen > RemainingRead ? RemainingRead : (UINTN)HoleLen;
>>      // Potential improvement: In the future, we could get the file hole's total
>>      // size and memset all that
>> -      SetMem (Buffer, WasRead, 0);
>> +      ZeroMem (Buffer, WasRead);
>>    } else {
>>      ExtentStartBytes = MultU64x32 (
>>                           LShiftU64 (Extent.ee_start_hi, 32) |
>> @@ -431,7 +431,7 @@ Ext4FileCreateTime (
>>  Inode = File->Inode;
>> 
>>  if (!EXT4_INODE_HAS_FIELD (Inode, i_crtime)) {
>> -    SetMem (Time, sizeof (EFI_TIME), 0);
>> +    ZeroMem (Time, sizeof (EFI_TIME));
>>    return;
>>  }
>> 
>> diff --git a/Features/Ext4Pkg/Ext4Dxe/Superblock.c b/Features/Ext4Pkg/Ext4Dxe/Superblock.c
>> index 47fc3a65507a..a57728a9abe6 100644
>> --- a/Features/Ext4Pkg/Ext4Dxe/Superblock.c
>> +++ b/Features/Ext4Pkg/Ext4Dxe/Superblock.c
>> @@ -257,16 +257,17 @@ Ext4OpenSuperblock (
>>    ));
>> 
>>  if (EXT4_IS_64_BIT (Partition)) {
>> +    // s_desc_size should be 4 byte aligned and
>> +    // 64 bit filesystems need DescSize to be 64 bytes
>> +    if (((Sb->s_desc_size % 4) != 0) || (Sb->s_desc_size < EXT4_64BIT_BLOCK_DESC_SIZE)) {
>> +      return EFI_VOLUME_CORRUPTED;
>> +    }
>> +
>>    Partition->DescSize = Sb->s_desc_size;
>>  } else {
>>    Partition->DescSize = EXT4_OLD_BLOCK_DESC_SIZE;
>>  }
>> 
>> -  if ((Partition->DescSize < EXT4_64BIT_BLOCK_DESC_SIZE) && EXT4_IS_64_BIT (Partition)) {
>> -    // 64 bit filesystems need DescSize to be 64 bytes
>> -    return EFI_VOLUME_CORRUPTED;
>> -  }
>> -
>>  if (!Ext4VerifySuperblockChecksum (Partition, Sb)) {
>>    DEBUG ((DEBUG_ERROR, "[ext4] Bad superblock checksum %lx\n", Ext4CalculateSuperblockChecksum (Partition, Sb)));
>>    return EFI_VOLUME_CORRUPTED;
>> @@ -342,7 +343,7 @@ Ext4CalculateChecksum (
>>      // For some reason, EXT4 really likes non-inverted CRC32C checksums, so we stick to that here.
>>      return ~CalculateCrc32c(Buffer, Length, ~InitialValue);
>>    default:
>> -      UNREACHABLE ();
>> +      ASSERT (FALSE);
>>      return 0;
>>  }
>> }
>> -- 
>> 2.37.0
>> 
> 

I already took into account all the remarks in v3, and will send it soon.

Best regards,
Savva Mitrofanov