Re: [PATCH 08/11] vfs: push EXDEV check down into ->remap_file_range

Dave Chinner
2018-12-03T23:40:32Z

On Mon, Dec 03, 2018 at 11:11:30AM -0800, Darrick J. Wong wrote:
> On Mon, Dec 03, 2018 at 01:04:07PM +0200, Amir Goldstein wrote:
> > On Mon, Dec 3, 2018 at 10:34 AM Dave Chinner <david@fromorbit.com> wrote:
> > >
> > > From: Dave Chinner <dchinner@redhat.com>
> > >
> > > before we can enable cross-device copies into copy_file_range(),
> > > we have to ensure that ->remap_file_range() implemenations will
> > > correctly reject attempts to do cross filesystem clones. Currently
> >
> > But you only fixed remap_file_range() implemenations of xfs and ocfs2...
> >
> > > these checks are done above calls to ->remap_file_range(), but
> > > we need to drive them inwards so that we get EXDEV protection for all
> > > callers of ->remap_file_range().
> > >
> > > Signed-off-by: Dave Chinner <dchinner@redhat.com>
> > > ---
> > > fs/read_write.c | 21 +++++++++++++--------
> > > 1 file changed, 13 insertions(+), 8 deletions(-)
> > >
> > > diff --git a/fs/read_write.c b/fs/read_write.c
> > > index 3288db1d5f21..174cf92eea1d 100644
> > > --- a/fs/read_write.c
> > > +++ b/fs/read_write.c
> > > @@ -1909,6 +1909,19 @@ int generic_remap_file_range_prep(struct file *file_in, loff_t pos_in,
> > > bool same_inode = (inode_in == inode_out);
> > > int ret;
> > >
> > > + /*
> > > + * FICLONE/FICLONERANGE ioctls enforce that src and dest files are on
> > > + * the same mount. Practically, they only need to be on the same file
> > > + * system. We check this here rather than at the ioctl layers because
> > > + * this is effectively a limitation of the fielsystem implementations,
> > > + * not so much the API itself. Further, ->remap_file_range() can be
> > > + * called from syscalls that don't have cross device copy restrictions
> > > + * (such as copy_file_range()) and so we need to catch them before we
> > > + * do any damage.
> > > + */
> > > + if (inode_in->i_sb != inode_out->i_sb)
> > > + return -EXDEV;
> > > +
> > > /* Don't touch certain kinds of inodes */
> > > if (IS_IMMUTABLE(inode_out))
> > > return -EPERM;
> > > @@ -2013,14 +2026,6 @@ loff_t do_clone_file_range(struct file *file_in, loff_t pos_in,
> > > if (!S_ISREG(inode_in->i_mode) || !S_ISREG(inode_out->i_mode))
> > > return -EINVAL;
> > >
> > > - /*
> > > - * FICLONE/FICLONERANGE ioctls enforce that src and dest files are on
> > > - * the same mount. Practically, they only need to be on the same file
> > > - * system.
> > > - */
> > > - if (inode_in->i_sb != inode_out->i_sb)
> > > - return -EXDEV;
> > > -
> >
>
> I think this is sort of backwards -- the checks should stay in
> do_clone_file_range, and vfs_copy_file_range should be calling that
> instead of directly calling ->remap_range():
>
> vfs_copy_file_range()
> {
> file_start_write(...);
> ret = do_clone_file_range(...);
> if (ret > 0)
> return ret;
> ret = do_copy_file_range(...);
> file_end_write(...);
> return ret;
> }

I'm already confused by the way we weave in and out of "vfs_/do_*"
functions, and this just makes it worse.

Just what the hell is supposed to be in a "vfs_" prefixed function,
and why the hell is it considered a "vfs" level function if we then
export it's internal functions for individual filesystems to use?

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com