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:

quoted

On Mon, Dec 3, 2018 at 10:34 AM Dave Chinner [off-list ref] wrote:

quoted

From: Dave Chinner <redacted>

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...

quoted

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 <redacted>
---
 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