Re: [edk2-platforms][PATCH v4 1/2] Ext4Pkg: Add symbolic links support

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

Looks very nice, tyvm. I did add a few more comments, but nothing critical at all.

Reviewed-by: Marvin Häuser <mhaeuser@posteo.de> as-is or with my comments addressed, either works.

> On 28. Jul 2022, at 17:26, Savva Mitrofanov <savvamtr@gmail.com> wrote:
> 
> BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3677
> 
> Provided support for symlink file type. Added routine which allows
> reading and following them through recursive open() call. As a security
> meausure implemented simple symlink loop check with nest level limit
> equal 8. Also this patch moves Ext4Open functionality to internal
> routine.
> 
> 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 |  13 +-
> Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h  |  98 +++++-
> Features/Ext4Pkg/Ext4Dxe/File.c     | 359 ++++++++++++++++++--
> Features/Ext4Pkg/Ext4Dxe/Inode.c    |  53 +++
> 4 files changed, 485 insertions(+), 38 deletions(-)
> 
> diff --git a/Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h b/Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h
> index a55cd2fa68ad..a73e3f8622f1 100644
> --- a/Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h
> +++ b/Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h
> @@ -171,7 +171,7 @@
> #define EXT4_DIRTY_FL         0x00000100
> #define EXT4_COMPRBLK_FL      0x00000200
> #define EXT4_NOCOMPR_FL       0x00000400
> -#define EXT4_ECOMPR_FL        0x00000800
> +#define EXT4_ENCRYPT_FL       0x00000800
> #define EXT4_BTREE_FL         0x00001000
> #define EXT4_INDEX_FL         0x00002000
> #define EXT4_JOURNAL_DATA_FL  0x00004000
> @@ -332,11 +332,12 @@ STATIC_ASSERT (
>   "ext4 block group descriptor struct has incorrect size"
>   );
> 
> -#define EXT4_DBLOCKS     12
> -#define EXT4_IND_BLOCK   12
> -#define EXT4_DIND_BLOCK  13
> -#define EXT4_TIND_BLOCK  14
> -#define EXT4_NR_BLOCKS   15
> +#define EXT4_DBLOCKS                12
> +#define EXT4_IND_BLOCK              12
> +#define EXT4_DIND_BLOCK             13
> +#define EXT4_TIND_BLOCK             14
> +#define EXT4_NR_BLOCKS              15
> +#define EXT4_FAST_SYMLINK_MAX_SIZE  EXT4_NR_BLOCKS * sizeof(UINT32)
> 
> #define EXT4_GOOD_OLD_INODE_SIZE  128
> 
> diff --git a/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h b/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h
> index b1508482b0a7..c1df9d1149e4 100644
> --- a/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h
> +++ b/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h
> @@ -31,7 +31,9 @@
> 
> #include "Ext4Disk.h"
> 
> +#define SYMLOOP_MAX    8
> #define EXT4_NAME_MAX  255
> +#define EFI_PATH_MAX   4096
> 
> #define EXT4_DRIVER_VERSION  0x0000
> 
> @@ -324,11 +326,11 @@ number of read bytes.
> **/
> EFI_STATUS
> Ext4Read (
> -  IN EXT4_PARTITION  *Partition,
> -  IN EXT4_FILE       *File,
> -  OUT VOID           *Buffer,
> -  IN UINT64          Offset,
> -  IN OUT UINTN       *Length
> +  IN     EXT4_PARTITION  *Partition,
> +  IN     EXT4_FILE       *File,
> +  OUT    VOID            *Buffer,
> +  IN     UINT64          Offset,
> +  IN OUT UINTN           *Length
>   );
> 
> /**
> @@ -368,6 +370,7 @@ struct _Ext4File {
> 
>   UINT64                OpenMode;
>   UINT64                Position;
> +  UINT32                SymLoops;
> 
>   EXT4_PARTITION        *Partition;
> 
> @@ -497,6 +500,45 @@ Ext4SetupFile (
>   IN EXT4_PARTITION  *Partition
>   );
> 
> +/**
> +  Opens a new file relative to the source file's location.
> +
> +  @param[out] FoundFile  A pointer to the location to return the opened handle for the new
> +                         file.
> +  @param[in]  Source     A pointer to the EXT4_FILE instance that is the file
> +                         handle to the source location. This would typically be an open
> +                         handle to a directory.
> +  @param[in]  FileName   The Null-terminated string of the name of the file to be opened.
> +                         The file name may contain the following path modifiers: "\", ".",
> +                         and "..".
> +  @param[in]  OpenMode   The mode to open the file. The only valid combinations that the
> +                         file may be opened with are: Read, Read/Write, or Create/Read/Write.
> +  @param[in]  Attributes Only valid for EFI_FILE_MODE_CREATE, in which case these are the
> +                         attribute bits for the newly created file.
> +
> +  @retval EFI_SUCCESS          The file was opened.
> +  @retval EFI_NOT_FOUND        The specified file could not be found on the device.
> +  @retval EFI_NO_MEDIA         The device has no medium.
> +  @retval EFI_MEDIA_CHANGED    The device has a different medium in it or the medium is no
> +                               longer supported.
> +  @retval EFI_DEVICE_ERROR     The device reported an error.
> +  @retval EFI_VOLUME_CORRUPTED The file system structures are corrupted.
> +  @retval EFI_WRITE_PROTECTED  An attempt was made to create a file, or open a file for write
> +                               when the media is write-protected.
> +  @retval EFI_ACCESS_DENIED    The service denied access to the file.
> +  @retval EFI_OUT_OF_RESOURCES Not enough resources were available to open the file.
> +  @retval EFI_VOLUME_FULL      The volume is full.
> +
> +**/
> +EFI_STATUS
> +Ext4OpenInternal (
> +  OUT EXT4_FILE  **FoundFile,
> +  IN  EXT4_FILE  *Source,
> +  IN  CHAR16     *FileName,
> +  IN  UINT64     OpenMode,
> +  IN  UINT64     Attributes
> +  );
> +
> /**
>    Closes a file.
> 
> @@ -774,6 +816,30 @@ Ext4FileIsDir (
>   IN CONST EXT4_FILE  *File
>   );
> 
> +/**
> +   Checks if a file is a symlink.
> +
> +   @param[in]      File          Pointer to the opened file.
> +
> +   @return BOOLEAN         Whether file is a symlink
> +**/
> +BOOLEAN
> +Ext4FileIsSymlink (
> +  IN CONST EXT4_FILE  *File
> +  );
> +
> +/**
> +   Detects if a symlink is a fast symlink.
> +
> +   @param[in]      File          Pointer to the opened file.
> +
> +   @return BOOLEAN         Whether symlink is a fast symlink
> +**/
> +BOOLEAN
> +Ext4SymlinkIsFastSymlink (
> +  IN CONST EXT4_FILE  *File
> +  );
> +
> /**
>    Checks if a file is a regular file.
>    @param[in]      File          Pointer to the opened file.
> @@ -797,7 +863,7 @@ Ext4FileIsReg (
>            it's a regular file or a directory, since most other file types
>            don't make sense under UEFI.
> **/
> -#define Ext4FileIsOpenable(File)  (Ext4FileIsReg(File) || Ext4FileIsDir(File))
> +#define Ext4FileIsOpenable(File)  (Ext4FileIsReg (File) || Ext4FileIsDir (File) || Ext4FileIsSymlink (File))
> 
> #define EXT4_INODE_HAS_FIELD(Inode, Field)                                     \
>   (Inode->i_extra_isize + EXT4_GOOD_OLD_INODE_SIZE >=                          \
> @@ -935,6 +1001,26 @@ Ext4ReadDir (
>   IN OUT UINTN       *OutLength
>   );
> 
> +/**
> +  Reads a symlink file.
> +
> +  @param[in]      Partition   Pointer to the ext4 partition.
> +  @param[in]      File        Pointer to the open symlink file.
> +  @param[out]     Symlink     Pointer to the output unicode symlink string.
> +
> +  @retval EFI_SUCCESS           Symlink was read.
> +  @retval EFI_ACCESS_DENIED     Symlink is encrypted.
> +  @retval EFI_OUT_OF_RESOURCES  Memory allocation error.
> +  @retval EFI_INVALID_PARAMETER Symlink path has incorrect length
> +  @retval EFI_VOLUME_CORRUPTED  Symlink read block size differ from inode value
> +**/
> +EFI_STATUS
> +Ext4ReadSymlink (
> +  IN     EXT4_PARTITION  *Partition,
> +  IN     EXT4_FILE       *File,
> +  OUT    CHAR16          **Symlink
> +  );
> +
> /**
>    Initialises the (empty) extents map, that will work as a cache of extents.
> 
> diff --git a/Features/Ext4Pkg/Ext4Dxe/File.c b/Features/Ext4Pkg/Ext4Dxe/File.c
> index ff1746d5640a..ae9230d6422b 100644
> --- a/Features/Ext4Pkg/Ext4Dxe/File.c
> +++ b/Features/Ext4Pkg/Ext4Dxe/File.c
> @@ -134,14 +134,224 @@ Ext4DirCanLookup (
>   return (File->Inode->i_mode & EXT4_INO_PERM_EXEC_OWNER) == EXT4_INO_PERM_EXEC_OWNER;
> }
> 
> +/**
> +  Reads a fast symlink file.
> +
> +  @param[in]      Partition   Pointer to the ext4 partition.
> +  @param[in]      File        Pointer to the open symlink file.
> +  @param[out]     AsciiSymlink     Pointer to the output ascii symlink string.
> +  @param[out]     AsciiSymlinkSize Pointer to the output ascii symlink string length.
> +
> +  @retval EFI_SUCCESS            Fast symlink was read.
> +  @retval EFI_OUT_OF_RESOURCES   Memory allocation error.
> +**/
> +STATIC
> +EFI_STATUS
> +Ext4ReadFastSymlink (
> +  IN     EXT4_PARTITION  *Partition,
> +  IN     EXT4_FILE       *File,
> +  OUT    CHAR8           **AsciiSymlink,
> +  OUT    UINT32          *AsciiSymlinkSize
> +  )
> +{
> +  UINT32  SymlinkSize;
> +  CHAR8   *AsciiSymlinkTmp;
> +  //
> +  // Fast-symlink's EXT4_INODE_SIZE is not necessarily validated when we checked it in
> +  // Ext4SymlinkIsFastSymlink(), so truncate if necessary.
> +  //
> +  SymlinkSize = (UINT32)MIN (EXT4_INODE_SIZE (File->Inode), EXT4_FAST_SYMLINK_MAX_SIZE);
> +
> +  AsciiSymlinkTmp = AllocatePool (SymlinkSize + 1);
> +  if (AsciiSymlinkTmp == NULL) {
> +    DEBUG ((DEBUG_FS, "[ext4] Failed to allocate symlink ascii string buffer\n"));
> +    return EFI_OUT_OF_RESOURCES;
> +  }
> +
> +  CopyMem (AsciiSymlinkTmp, File->Inode->i_data, SymlinkSize);
> +
> +  //
> +  // Add null-terminator
> +  //
> +  AsciiSymlinkTmp[SymlinkSize] = '\0';
> +
> +  *AsciiSymlink     = AsciiSymlinkTmp;
> +  *AsciiSymlinkSize = SymlinkSize + 1;
> +
> +  return EFI_SUCCESS;
> +}
> +
> +/**
> +  Reads a slow symlink file.
> +
> +  @param[in]      Partition        Pointer to the ext4 partition.
> +  @param[in]      File             Pointer to the open symlink file.
> +  @param[out]     AsciiSymlink     Pointer to the output ascii symlink string.
> +  @param[out]     AsciiSymlinkSize Pointer to the output ascii symlink string length.
> +
> +  @retval EFI_SUCCESS           Slow symlink was read.
> +  @retval EFI_OUT_OF_RESOURCES  Memory allocation error.
> +  @retval EFI_INVALID_PARAMETER Slow symlink path has incorrect length
> +  @retval EFI_VOLUME_CORRUPTED  Symlink read block size differ from inode value
> +**/
> +STATIC
> +EFI_STATUS
> +Ext4ReadSlowSymlink (
> +  IN     EXT4_PARTITION  *Partition,
> +  IN     EXT4_FILE       *File,
> +  OUT    CHAR8           **AsciiSymlink,
> +  OUT    UINT32          *AsciiSymlinkSize
> +  )
> +{
> +  EFI_STATUS  Status;
> +  CHAR8       *SymlinkTmp;
> +  UINT64      SymlinkSizeTmp;
> +  UINT32      SymlinkAllocateSize;
> +  UINTN       ReadSize;
> +
> +  SymlinkSizeTmp = EXT4_INODE_SIZE (File->Inode);
> +
> +  //
> +  // Allocate EXT4_INODE_SIZE + 1
> +  //
> +  if (SymlinkSizeTmp > EFI_PATH_MAX - 1) {
> +    DEBUG ((
> +      DEBUG_FS,
> +      "[ext4] Error! Symlink path maximum length was hit!\n"
> +      ));
> +    return EFI_INVALID_PARAMETER;
> +  }
> +
> +  SymlinkAllocateSize = (UINT32)SymlinkSizeTmp + 1;
> +
> +  SymlinkTmp = AllocatePool (SymlinkAllocateSize);
> +  if (SymlinkTmp == NULL) {
> +    DEBUG ((DEBUG_FS, "[ext4] Failed to allocate symlink ascii string buffer\n"));
> +    return EFI_OUT_OF_RESOURCES;
> +  }
> +
> +  ReadSize = (UINTN)SymlinkSizeTmp;
> +  Status   = Ext4Read (Partition, File, SymlinkTmp, File->Position, &ReadSize);
> +  if (EFI_ERROR (Status)) {
> +    DEBUG ((DEBUG_FS, "[ext4] Failed to read symlink from blocks with Status %r\n", Status));
> +    FreePool (SymlinkTmp);
> +    return Status;
> +  }
> +
> +  File->Position += ReadSize;
> +
> +  //
> +  // Add null-terminator
> +  //
> +  SymlinkTmp[SymlinkSizeTmp] = '\0';
> +
> +  if (SymlinkSizeTmp != ReadSize) {
> +    DEBUG ((
> +      DEBUG_FS,
> +      "[ext4] Error! The sz of the read block doesn't match the value from the inode!\n"
> +      ));
> +    return EFI_VOLUME_CORRUPTED;
> +  }
> +
> +  *AsciiSymlinkSize = SymlinkAllocateSize;
> +  *AsciiSymlink     = SymlinkTmp;
> +
> +  return EFI_SUCCESS;
> +}
> +
> +/**
> +  Reads a symlink file.
> +
> +  @param[in]      Partition   Pointer to the ext4 partition.
> +  @param[in]      File        Pointer to the open symlink file.
> +  @param[out]     Symlink     Pointer to the output unicode symlink string.
> +
> +  @retval EFI_SUCCESS           Symlink was read.
> +  @retval EFI_ACCESS_DENIED     Symlink is encrypted.
> +  @retval EFI_OUT_OF_RESOURCES  Memory allocation error.
> +  @retval EFI_INVALID_PARAMETER Symlink path has incorrect length
> +  @retval EFI_VOLUME_CORRUPTED  Symlink read block size differ from inode value
> +**/
> +EFI_STATUS
> +Ext4ReadSymlink (
> +  IN     EXT4_PARTITION  *Partition,
> +  IN     EXT4_FILE       *File,
> +  OUT    CHAR16          **Symlink
> +  )
> +{
> +  EFI_STATUS  Status;
> +  CHAR8       *SymlinkTmp;
> +  UINT32      SymlinkSize;
> +  CHAR16      *Symlink16Tmp;
> +  CHAR16      *Needle;
> +
> +  //
> +  // Assume that we alread read Inode via Ext4ReadInode
> +  // Skip reading, just check encryption flag
> +  //
> +  if ((File->Inode->i_flags & EXT4_ENCRYPT_FL) != 0) {
> +    DEBUG ((DEBUG_FS, "[ext4] Error, symlink is encrypted\n"));
> +    return EFI_ACCESS_DENIED;
> +  }
> +
> +  if (Ext4SymlinkIsFastSymlink (File)) {
> +    Status = Ext4ReadFastSymlink (Partition, File, &SymlinkTmp, &SymlinkSize);
> +  } else {
> +    Status = Ext4ReadSlowSymlink (Partition, File, &SymlinkTmp, &SymlinkSize);
> +  }
> +
> +  if (EFI_ERROR (Status)) {
> +    DEBUG ((DEBUG_FS, "[ext4] Symlink read error with Status %r\n", Status));
> +    return Status;
> +  }
> +
> +  Symlink16Tmp = AllocateZeroPool (SymlinkSize * sizeof (CHAR16));

Any specific reason to use ZeroPool here, when the rest of the code doesn’t?

> +  if (Symlink16Tmp == NULL) {
> +    DEBUG ((DEBUG_FS, "[ext4] Failed to allocate symlink unicode string buffer\n"));
> +    FreePool (SymlinkTmp);
> +    return EFI_OUT_OF_RESOURCES;
> +  }
> +
> +  Status = AsciiStrToUnicodeStrS (
> +             SymlinkTmp,
> +             Symlink16Tmp,
> +             SymlinkSize
> +             );

Can’t SymlinkTmp be free’d here?

> +
> +  if (EFI_ERROR (Status)) {
> +    DEBUG ((
> +      DEBUG_FS,
> +      "[ext4] Failed to convert ascii symlink to unicode with Status %r\n",
> +      Status
> +      ));
> +    FreePool (Symlink16Tmp);
> +    FreePool (SymlinkTmp);
> +    return Status;
> +  }
> +
> +  //
> +  // Convert to UEFI slashes
> +  //
> +  for (Needle = Symlink16Tmp; *Needle != L'\0'; Needle++) {
> +    if (*Needle == L'/') {
> +      *Needle = L'\\';
> +    }
> +  }
> +
> +  *Symlink = Symlink16Tmp;
> +
> +  FreePool (SymlinkTmp);
> +  return Status;
> +}
> +
> /**
>   Opens a new file relative to the source file's location.
> 
> -  @param[in]  This       A pointer to the EFI_FILE_PROTOCOL instance that is the file
> +  @param[out] FoundFile  A pointer to the location to return the opened handle for the new
> +                         file.
> +  @param[in]  Source     A pointer to the EXT4_FILE instance that is the file
>                          handle to the source location. This would typically be an open
>                          handle to a directory.
> -  @param[out] NewHandle  A pointer to the location to return the opened handle for the new
> -                         file.
>   @param[in]  FileName   The Null-terminated string of the name of the file to be opened.
>                          The file name may contain the following path modifiers: "\", ".",
>                          and "..".
> @@ -165,13 +375,12 @@ Ext4DirCanLookup (
> 
> **/
> EFI_STATUS
> -EFIAPI
> -Ext4Open (
> -  IN EFI_FILE_PROTOCOL   *This,
> -  OUT EFI_FILE_PROTOCOL  **NewHandle,
> -  IN CHAR16              *FileName,
> -  IN UINT64              OpenMode,
> -  IN UINT64              Attributes
> +Ext4OpenInternal (
> +  OUT EXT4_FILE  **FoundFile,
> +  IN  EXT4_FILE  *Source,
> +  IN  CHAR16     *FileName,
> +  IN  UINT64     OpenMode,
> +  IN  UINT64     Attributes
>   )
> {
>   EXT4_FILE       *Current;
> @@ -180,13 +389,14 @@ Ext4Open (
>   CHAR16          PathSegment[EXT4_NAME_MAX + 1];
>   UINTN           Length;
>   EXT4_FILE       *File;
> +  CHAR16          *Symlink;
>   EFI_STATUS      Status;
> 
> -  Current   = (EXT4_FILE *)This;
> +  Current   = Source;
>   Partition = Current->Partition;
>   Level     = 0;
> 
> -  DEBUG ((DEBUG_FS, "[ext4] Ext4Open %s\n", FileName));
> +  DEBUG ((DEBUG_FS, "[ext4] Ext4OpenInternal %s\n", FileName));
>   // If the path starts with a backslash, we treat the root directory as the base directory
>   if (FileName[0] == L'\\') {
>     FileName++;
> @@ -194,6 +404,11 @@ Ext4Open (
>   }
> 
>   while (FileName[0] != L'\0') {
> +    if (Partition->Root->SymLoops > SYMLOOP_MAX) {
> +      DEBUG ((DEBUG_FS, "[ext4] Symloop limit is hit !\n"));
> +      return EFI_ACCESS_DENIED;
> +    }
> +
>     // Discard leading path separators
>     while (FileName[0] == L'\\') {
>       FileName++;
> @@ -238,18 +453,45 @@ Ext4Open (
>     }
> 
>     // Check if this is a valid file to open in EFI
> -
> -    // What to do with symlinks? They're nonsense when absolute but may
> -    // be useful when they're relative. Right now, they're ignored, since they
> -    // bring a lot of trouble for something that's not as useful in our case.
> -    // If you want to link, use hard links.
> -
>     if (!Ext4FileIsOpenable (File)) {
>       Ext4CloseInternal (File);
>       // This looks like an /okay/ status to return.
>       return EFI_ACCESS_DENIED;
>     }
> 
> +    //
> +    // Reading symlink and then trying to follow it
> +    //
> +    if (Ext4FileIsSymlink (File)) {
> +      Partition->Root->SymLoops++;
> +      DEBUG ((DEBUG_FS, "[ext4] File %s is symlink, trying to read it\n", PathSegment));
> +      Status = Ext4ReadSymlink (Partition, File, &Symlink);
> +      if (EFI_ERROR (Status)) {
> +        DEBUG ((DEBUG_FS, "[ext4] Error reading %s symlink!\n", PathSegment));
> +        return Status;
> +      }
> +
> +      DEBUG ((DEBUG_FS, "[ext4] File %s is linked to %s\n", PathSegment, Symlink));
> +      //
> +      // Close symlink file
> +      //
> +      Ext4CloseInternal (File);
> +      //
> +      // Open linked file by recursive call of Ext4OpenFile
> +      //
> +      Status = Ext4OpenInternal (FoundFile, Current, Symlink, OpenMode, Attributes);
> +      FreePool (Symlink);
> +      if (EFI_ERROR (Status)) {
> +        DEBUG ((DEBUG_FS, "[ext4] Error opening linked file %s\n", Symlink));
> +        return Status;
> +      }
> +
> +      //
> +      // Set File to newly opened
> +      //
> +      File = *FoundFile;
> +    }
> +
>     if (Level != 0) {
>       // Careful not to close the base directory
>       Ext4CloseInternal (Current);
> @@ -273,12 +515,75 @@ Ext4Open (
>     return EFI_ACCESS_DENIED;
>   }
> 
> -  *NewHandle = &Current->Protocol;
> +  *FoundFile = Current;
> 
>   DEBUG ((DEBUG_FS, "[ext4] Opened filename %s\n", Current->Dentry->Name));
>   return EFI_SUCCESS;
> }
> 
> +/**
> +  Opens a new file relative to the source file's location.
> +  @param[in]  This       A pointer to the EFI_FILE_PROTOCOL instance that is the file
> +                         handle to the source location. This would typically be an open
> +                         handle to a directory.
> +  @param[out] NewHandle  A pointer to the location to return the opened handle for the new
> +                         file.
> +  @param[in]  FileName   The Null-terminated string of the name of the file to be opened.
> +                         The file name may contain the following path modifiers: "\", ".",
> +                         and "..".
> +  @param[in]  OpenMode   The mode to open the file. The only valid combinations that the
> +                         file may be opened with are: Read, Read/Write, or Create/Read/Write.
> +  @param[in]  Attributes Only valid for EFI_FILE_MODE_CREATE, in which case these are the
> +                         attribute bits for the newly created file.
> +  @retval EFI_SUCCESS          The file was opened.
> +  @retval EFI_NOT_FOUND        The specified file could not be found on the device.
> +  @retval EFI_NO_MEDIA         The device has no medium.
> +  @retval EFI_MEDIA_CHANGED    The device has a different medium in it or the medium is no
> +                               longer supported.
> +  @retval EFI_DEVICE_ERROR     The device reported an error.
> +  @retval EFI_VOLUME_CORRUPTED The file system structures are corrupted.
> +  @retval EFI_WRITE_PROTECTED  An attempt was made to create a file, or open a file for write
> +                               when the media is write-protected.
> +  @retval EFI_ACCESS_DENIED    The service denied access to the file.
> +  @retval EFI_OUT_OF_RESOURCES Not enough resources were available to open the file.
> +  @retval EFI_VOLUME_FULL      The volume is full.
> +**/
> +EFI_STATUS
> +EFIAPI
> +Ext4Open (
> +  IN EFI_FILE_PROTOCOL   *This,
> +  OUT EFI_FILE_PROTOCOL  **NewHandle,
> +  IN CHAR16              *FileName,
> +  IN UINT64              OpenMode,
> +  IN UINT64              Attributes
> +  )
> +{
> +  EFI_STATUS  Status;
> +  EXT4_FILE   *FoundFile;
> +  EXT4_FILE   *Source;
> +
> +  Source = (EXT4_FILE *)This;
> +
> +  //
> +  // Reset SymLoops counter
> +  //
> +  Source->Partition->Root->SymLoops = 0;
> +
> +  Status = Ext4OpenInternal (
> +             &FoundFile,
> +             Source,
> +             FileName,
> +             OpenMode,
> +             Attributes
> +             );
> +
> +  if (!EFI_ERROR (Status)) {
> +    *NewHandle = &FoundFile->Protocol;
> +  }
> +
> +  return Status;
> +}
> +
> /**
>   Closes a specified file handle.
> 
> @@ -588,7 +893,7 @@ Ext4GetVolumeName (
> 
>   // s_volume_name is only valid on dynamic revision; old filesystems don't support this
>   if (Partition->SuperBlock.s_rev_level == EXT4_DYNAMIC_REV) {
> -    CopyMem (TempVolName, (CONST CHAR8 *)Partition->SuperBlock.s_volume_name, 16);
> +    CopyMem (TempVolName, Partition->SuperBlock.s_volume_name, 16);
>     TempVolName[16] = '\0';
> 
>     Status = UTF8StrToUCS2 (TempVolName, &VolumeName);
> @@ -754,12 +1059,14 @@ Ext4GetInfo (
>   OUT VOID              *Buffer
>   )
> {
> +  EXT4_FILE       *File;
>   EXT4_PARTITION  *Partition;
> 
> -  Partition = ((EXT4_FILE *)This)->Partition;
> +  File      = (EXT4_FILE *)This;
> +  Partition = File->Partition;
> 
>   if (CompareGuid (InformationType, &gEfiFileInfoGuid)) {
> -    return Ext4GetFileInfo ((EXT4_FILE *)This, Buffer, BufferSize);
> +    return Ext4GetFileInfo (File, Buffer, BufferSize);
>   }
> 
>   if (CompareGuid (InformationType, &gEfiFileSystemInfoGuid)) {
> @@ -870,12 +1177,12 @@ Ext4SetInfo (
>   )
> {
>   EXT4_FILE       *File;
> -  EXT4_PARTITION  *Part;
> +  EXT4_PARTITION  *Partition;
> 
> -  File = (EXT4_FILE *)This;
> -  Part = File->Partition;
> +  File      = (EXT4_FILE *)This;
> +  Partition = File->Partition;
> 
> -  if (Part->ReadOnly) {
> +  if (Partition->ReadOnly) {
>     return EFI_WRITE_PROTECTED;
>   }
> 
> diff --git a/Features/Ext4Pkg/Ext4Dxe/Inode.c b/Features/Ext4Pkg/Ext4Dxe/Inode.c
> index 831f5946e870..e7a6b3225709 100644
> --- a/Features/Ext4Pkg/Ext4Dxe/Inode.c
> +++ b/Features/Ext4Pkg/Ext4Dxe/Inode.c
> @@ -255,6 +255,59 @@ Ext4FileIsDir (
>   return (File->Inode->i_mode & EXT4_INO_TYPE_DIR) == EXT4_INO_TYPE_DIR;
> }
> 
> +/**
> +   Checks if a file is a symlink.
> +
> +   @param[in]      File          Pointer to the opened file.
> +
> +   @return BOOLEAN         Whether file is a symlink
> +**/
> +BOOLEAN
> +Ext4FileIsSymlink (
> +  IN CONST EXT4_FILE  *File
> +  )
> +{
> +  return (File->Inode->i_mode & EXT4_INO_TYPE_SYMLINK) == EXT4_INO_TYPE_SYMLINK;
> +}
> +
> +/**
> +   Detects if a symlink is a fast symlink.
> +
> +   @param[in]      File          Pointer to the opened file.
> +
> +   @return BOOLEAN         Whether symlink is a fast symlink
> +**/
> +BOOLEAN
> +Ext4SymlinkIsFastSymlink (
> +  IN CONST EXT4_FILE  *File
> +  )
> +{
> +  //
> +  // Detection logic of the fast-symlink splits into two behaviors - old and new.
> +  // The old behavior is based on comparing the extended attribute blocks
> +  // with the inode's i_blocks, and if it's zero we know the inode isn't storing
> +  // the link in filesystem blocks, so we look to the inode->i_data.
> +  // The new behavior is apparently needed only with the large EA inode feature.
> +  // In this case we check that inode size less than maximum fast symlink size.
> +  // So, we revert to the old behavior if the large EA inode feature is not set.
> +  //
> +  UINT32  FileAcl;
> +  UINT32  ExtAttrBlocks;
> +
> +  if ((File->Inode->i_flags & EXT4_EA_INODE_FL) == 0) {
> +    FileAcl = File->Inode->i_file_acl;
> +    if (EXT4_IS_64_BIT (File->Partition)) {
> +      FileAcl |= LShiftU64 (File->Inode->i_osd2.data_linux.l_i_file_acl_high, 32);

*If* you happen to do a new revision anyway, you could drop the shift (with a comment!) if you want, because we don’t care about the actual value, just whether any one bit is set. Don’t bother if there won’t be a new revision anyway, though. :)

> +    }
> +
> +    ExtAttrBlocks = FileAcl != 0 ? (File->Partition->BlockSize >> 9) : 0;
> +
> +    return File->Inode->i_blocks == ExtAttrBlocks;
> +  }
> +
> +  return EXT4_INODE_SIZE (File->Inode) <= EXT4_FAST_SYMLINK_MAX_SIZE;
> +}
> +
> /**
>    Checks if a file is a regular file.
>    @param[in]      File          Pointer to the opened file.
> -- 
> 2.37.1
>