remap_range: merge do_clone_file_range() into vfs_clone_file_range()

commit dfad370 ("remap_range: move permission hooks out of
do_clone_file_range()") moved the permission hooks from
do_clone_file_range() out to its caller vfs_clone_file_range(),
but left all the fast sanity checks in do_clone_file_range().

This makes the expensive security hooks be called in situations
that they would not have been called before (e.g. fs does not support
clone).

The only reason for the do_clone_file_range() helper was that overlayfs
did not use to be able to call vfs_clone_file_range() from copy up
context with sb_writers lock held.  However, since commit c63e56a
("ovl: do not open/llseek lower file with upper sb_writers held"),
overlayfs just uses an open coded version of vfs_clone_file_range().

Merge_clone_file_range() into vfs_clone_file_range(), restoring the
original order of checks as it was before the regressing commit and adapt
the overlayfs code to call vfs_clone_file_range() before the permission
hooks that were added by commit ca7ab48 ("ovl: add permission hooks
outside of do_splice_direct()").

Note that in the merge of do_clone_file_range(), the file_start_write()
context was reduced to cover ->remap_file_range() without holding it
over the permission hooks, which was the reason for doing the regressing
commit in the first place.

Reported-and-tested-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202401312229.eddeb9a6-oliver.sang@intel.com
Fixes: dfad370 ("remap_range: move permission hooks out of do_clone_file_range()")
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Link: https://lore.kernel.org/r/20240202102258.1582671-1-amir73il@gmail.com
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: amir73il

fs/overlayfs/copy_up.c

@@ -265,20 +265,18 @@ static int ovl_copy_up_file(struct ovl_fs *ofs, struct dentry *dentry,
 	if (IS_ERR(old_file))
 		return PTR_ERR(old_file);
 
+	/* Try to use clone_file_range to clone up within the same fs */
+	cloned = vfs_clone_file_range(old_file, 0, new_file, 0, len, 0);
+	if (cloned == len)
+		goto out_fput;
+
+	/* Couldn't clone, so now we try to copy the data */
 	error = rw_verify_area(READ, old_file, &old_pos, len);
 	if (!error)
 		error = rw_verify_area(WRITE, new_file, &new_pos, len);
 	if (error)
 		goto out_fput;
 
-	/* Try to use clone_file_range to clone up within the same fs */
-	ovl_start_write(dentry);
-	cloned = do_clone_file_range(old_file, 0, new_file, 0, len, 0);
-	ovl_end_write(dentry);
-	if (cloned == len)
-		goto out_fput;
-	/* Couldn't clone, so now we try to copy the data */
-
 	/* Check if lower fs supports seek operation */
 	if (old_file->f_mode & FMODE_LSEEK)
 		skip_hole = true;

fs/remap_range.c

@@ -373,9 +373,9 @@ int generic_remap_file_range_prep(struct file *file_in, loff_t pos_in,
 }
 EXPORT_SYMBOL(generic_remap_file_range_prep);
 
-loff_t do_clone_file_range(struct file *file_in, loff_t pos_in,
-			   struct file *file_out, loff_t pos_out,
-			   loff_t len, unsigned int remap_flags)
+loff_t vfs_clone_file_range(struct file *file_in, loff_t pos_in,
+			    struct file *file_out, loff_t pos_out,
+			    loff_t len, unsigned int remap_flags)
 {
 	loff_t ret;
 
@@ -391,23 +391,6 @@ loff_t do_clone_file_range(struct file *file_in, loff_t pos_in,
 	if (!file_in->f_op->remap_file_range)
 		return -EOPNOTSUPP;
 
-	ret = file_in->f_op->remap_file_range(file_in, pos_in,
-			file_out, pos_out, len, remap_flags);
-	if (ret < 0)
-		return ret;
-
-	fsnotify_access(file_in);
-	fsnotify_modify(file_out);
-	return ret;
-}
-EXPORT_SYMBOL(do_clone_file_range);
-
-loff_t vfs_clone_file_range(struct file *file_in, loff_t pos_in,
-			    struct file *file_out, loff_t pos_out,
-			    loff_t len, unsigned int remap_flags)
-{
-	loff_t ret;
-
 	ret = remap_verify_area(file_in, pos_in, len, false);
 	if (ret)
 		return ret;
@@ -417,10 +400,14 @@ loff_t vfs_clone_file_range(struct file *file_in, loff_t pos_in,
 		return ret;
 
 	file_start_write(file_out);
-	ret = do_clone_file_range(file_in, pos_in, file_out, pos_out, len,
-				  remap_flags);
+	ret = file_in->f_op->remap_file_range(file_in, pos_in,
+			file_out, pos_out, len, remap_flags);
 	file_end_write(file_out);
+	if (ret < 0)
+		return ret;
 
+	fsnotify_access(file_in);
+	fsnotify_modify(file_out);
 	return ret;
 }
 EXPORT_SYMBOL(vfs_clone_file_range);

include/linux/fs.h

@@ -2101,9 +2101,6 @@ int __generic_remap_file_range_prep(struct file *file_in, loff_t pos_in,
 int generic_remap_file_range_prep(struct file *file_in, loff_t pos_in,
 				  struct file *file_out, loff_t pos_out,
 				  loff_t *count, unsigned int remap_flags);
-extern loff_t do_clone_file_range(struct file *file_in, loff_t pos_in,
-				  struct file *file_out, loff_t pos_out,
-				  loff_t len, unsigned int remap_flags);
 extern loff_t vfs_clone_file_range(struct file *file_in, loff_t pos_in,
 				   struct file *file_out, loff_t pos_out,
 				   loff_t len, unsigned int remap_flags);