smb/client: use writable handle for FS_IOC_SETFLAGS compression

Setting the compressed flag on a CIFS mount can fail with -EACCES:

	[compress_share]
		vfs objects = btrfs

        $ touch test.bin
        $ chattr +c test.bin
        chattr: Permission denied while setting flags on test.bin

This can be reproduced against a Samba share backed by a filesystem that
supports compression, such as btrfs.

FS_IOC_SETFLAGS is issued on the file handle opened by userspace.  chattr
opens the target read-only before setting FS_COMPR_FL, so the SMB client
currently sends FSCTL_SET_COMPRESSION on a handle that may not have
FILE_WRITE_DATA access.  Samba requires FILE_WRITE_DATA for
FSCTL_SET_COMPRESSION and rejects the request.

Use the current handle only if it already has FILE_WRITE_DATA.  Otherwise
try an existing writable handle for the inode.  If none is available, open
a temporary FILE_WRITE_DATA handle for the compression request.

After FSCTL_SET_COMPRESSION succeeds, update the cached compressed
attribute immediately, matching how smb2_set_sparse() updates
FILE_ATTRIBUTE_SPARSE_FILE after a successful FSCTL_SET_SPARSE.

Signed-off-by: Huiwen He <hehuiwen@kylinos.cn>
Reviewed-by: ChenXiaoSong <chenxiaosong@kylinos.cn>
Signed-off-by: Steve French <stfrench@microsoft.com>

0 files changed, 0 insertions, 0 deletions