Currently, project quota could be changed by fssetxattr
ioctl, and existed permission check inode_owner_or_capable()
is obviously not enough, just think that common users could
change project id of file, that could make users to
break project quota easily.

This patch try to follow same regular of xfs project
quota:

"Project Quota ID state is only allowed to change from
within the init namespace. Enforce that restriction only
if we are trying to change the quota ID state.
Everything else is allowed in user namespaces."

Besides that, check and set project id'state should
be an atomic operation, protect whole operation with
inode lock, ext4_ioctl_setproject() is only used for
ioctl EXT4_IOC_FSSETXATTR, we have held mnt_want_write_file()
before ext4_ioctl_setflags(), and ext4_ioctl_setproject()
is called after ext4_ioctl_setflags(), we could share
codes, so remove it inside ext4_ioctl_setproject().

Signed-off-by: Wang Shilong <wshilong@ddn.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Cc: stable@kernel.org