Several questions have popped up regarding the ext4 directory entry layout and contents off-list. Attempt to clarify these issues by adding some explanatory comments.
Signed-off-by: Pedro Falcato <[email protected]> Cc: Marvin Häuser <[email protected]> --- Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h | 18 +++++++++++++++++- Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h | 3 +-- 2 files changed, 18 insertions(+), 3 deletions(-) diff --git a/Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h b/Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h index 4fd91a423324..2dad967e575d 100644 --- a/Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h +++ b/Features/Ext4Pkg/Ext4Dxe/Ext4Disk.h @@ -397,12 +397,28 @@ typedef struct _Ext4Inode { UINT32 i_projid; } EXT4_INODE; +#define EXT4_NAME_MAX 255 + typedef struct { + // ext4 directory entries are layed out in the following fashion: + // offset 0x0: UINT32 inode number (if 0, unused entry, should skip.) + // offset 0x4: UINT16 rec_len: Dir entry's length. + // Note: rec_len >= name_len + EXT4_MIN_DIR_ENTRY_LEN and rec_len % 4 == 0. + // offset 0x6: UINT8 name_len: Dir entry's name's length + // offset 0x7: UINT8 file_type Dir entry's file type indicator + // offset 0x8: CHAR8 name[name_len]: Variable length character array; not null-terminated. + // + // Further note: ext4 directories are defined, as the documentation puts it, as: + // "a directory is more or less a flat file that maps an arbitrary byte string + // (usually ASCII) to an inode number on the filesystem". So, they are not + // necessarily encoded with ASCII, UTF-8, or any of the sort. We must treat it + // as a bag of bytes. When interacting with EFI interfaces themselves (which expect UCS-2) + // we skip any directory entry that is not valid UTF-8. UINT32 inode; UINT16 rec_len; UINT8 name_len; UINT8 file_type; - CHAR8 name[255]; + CHAR8 name[EXT4_NAME_MAX]; } EXT4_DIR_ENTRY; #define EXT4_MIN_DIR_ENTRY_LEN 8 diff --git a/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h b/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h index adf3c13f6ea9..81ba568c5947 100644 --- a/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h +++ b/Features/Ext4Pkg/Ext4Dxe/Ext4Dxe.h @@ -31,8 +31,7 @@ #include "Ext4Disk.h" -#define SYMLOOP_MAX 8 -#define EXT4_NAME_MAX 255 +#define SYMLOOP_MAX 8 // // We need to specify path length limit for security purposes, to prevent possible // overflows and dead-loop conditions. Originally this limit is absent in FS design, -- 2.39.0 -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. View/Reply Online (#98320): https://edk2.groups.io/g/devel/message/98320 Mute This Topic: https://groups.io/mt/96211960/21656 Group Owner: [email protected] Unsubscribe: https://edk2.groups.io/g/devel/unsub [[email protected]] -=-=-=-=-=-=-=-=-=-=-=-
