Commit 06a7adf3 authored by Pali Rohár's avatar Pali Rohár Committed by Steve French
Browse files

cifs: Add support for parsing WSL-style symlinks 



Linux CIFS client currently does not implement readlink() for WSL-style
symlinks. It is only able to detect that file is of WSL-style symlink, but
is not able to read target symlink location.

Add this missing functionality and implement support for parsing content of
WSL-style symlink.

The important note is that symlink target location stored for WSL symlink
reparse point (IO_REPARSE_TAG_LX_SYMLINK) is in UTF-8 encoding instead of
UTF-16 (which is used in whole SMB protocol and also in all other symlink
styles). So for proper locale/cp support it is needed to do conversion from
UTF-8 to local_nls.

Signed-off-by: default avatarPali Rohár <pali@kernel.org>
Signed-off-by: default avatarSteve French <stfrench@microsoft.com>
parent dd26bc06

fs/smb/client/reparse.c

+49 −0
Original line number Diff line number Diff line
@@ -647,6 +647,52 @@ static int parse_reparse_symlink(struct reparse_symlink_data_buffer *sym, 
					 cifs_sb);

}



static int parse_reparse_wsl_symlink(struct reparse_wsl_symlink_data_buffer *buf,

				     struct cifs_sb_info *cifs_sb,

				     struct cifs_open_info_data *data)

{

	int len = le16_to_cpu(buf->ReparseDataLength);

	int symname_utf8_len;

	__le16 *symname_utf16;

	int symname_utf16_len;



	if (len <= sizeof(buf->Flags)) {

		cifs_dbg(VFS, "srv returned malformed wsl symlink buffer\n");

		return -EIO;

	}



	/* PathBuffer is in UTF-8 but without trailing null-term byte */

	symname_utf8_len = len - sizeof(buf->Flags);

	/*

	 * Check that buffer does not contain null byte

	 * because Linux cannot process symlink with null byte.

	 */

	if (strnlen(buf->PathBuffer, symname_utf8_len) != symname_utf8_len) {

		cifs_dbg(VFS, "srv returned null byte in wsl symlink target location\n");

		return -EIO;

	}

	symname_utf16 = kzalloc(symname_utf8_len * 2, GFP_KERNEL);

	if (!symname_utf16)

		return -ENOMEM;

	symname_utf16_len = utf8s_to_utf16s(buf->PathBuffer, symname_utf8_len,

					    UTF16_LITTLE_ENDIAN,

					    symname_utf16, symname_utf8_len * 2);

	if (symname_utf16_len < 0) {

		kfree(symname_utf16);

		return symname_utf16_len;

	}

	symname_utf16_len *= 2; /* utf8s_to_utf16s() returns number of u16 items, not byte length */



	data->symlink_target = cifs_strndup_from_utf16((u8 *)symname_utf16,

						       symname_utf16_len, true,

						       cifs_sb->local_nls);

	kfree(symname_utf16);

	if (!data->symlink_target)

		return -ENOMEM;



	return 0;

}



int parse_reparse_point(struct reparse_data_buffer *buf,

			u32 plen, struct cifs_sb_info *cifs_sb,

			const char *full_path,
@@ -666,6 +712,9 @@ int parse_reparse_point(struct reparse_data_buffer *buf, 
			(struct reparse_symlink_data_buffer *)buf,

			plen, unicode, cifs_sb, full_path, data);

	case IO_REPARSE_TAG_LX_SYMLINK:

		return parse_reparse_wsl_symlink(

			(struct reparse_wsl_symlink_data_buffer *)buf,

			cifs_sb, data);

	case IO_REPARSE_TAG_AF_UNIX:

	case IO_REPARSE_TAG_LX_FIFO:

	case IO_REPARSE_TAG_LX_CHR:

fs/smb/common/smb2pdu.h

+9 −0
Original line number Diff line number Diff line
@@ -1552,6 +1552,15 @@ struct reparse_symlink_data_buffer { 


/* See MS-FSCC 2.1.2.6 and cifspdu.h for struct reparse_posix_data */



/* For IO_REPARSE_TAG_LX_SYMLINK */

struct reparse_wsl_symlink_data_buffer {

	__le32	ReparseTag;

	__le16	ReparseDataLength;

	__u16	Reserved;

	__le32	Flags;

	__u8	PathBuffer[]; /* Variable Length UTF-8 string without nul-term */

} __packed;



struct validate_negotiate_info_req {

	__le32 Capabilities;

	__u8   Guid[SMB2_CLIENT_GUID_SIZE];