vfs: remap helper should update destination inode metadata

Extend generic_remap_file_range_prep to handle inode metadata updates
when remapping into a file.  If the operation can possibly alter the
file contents, we must update the ctime and mtime and remove security
privileges, just like we do for regular file writes.
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/read_write.c

@@ -1820,6 +1820,25 @@ int generic_remap_file_range_prep(struct file *file_in, loff_t pos_in,
 	if (ret)
 		return ret;
 
+	/* If can't alter the file contents, we're done. */
+	if (!(remap_flags & REMAP_FILE_DEDUP)) {
+		/* Update the timestamps, since we can alter file contents. */
+		if (!(file_out->f_mode & FMODE_NOCMTIME)) {
+			ret = file_update_time(file_out);
+			if (ret)
+				return ret;
+		}
+
+		/*
+		 * Clear the security bits if the process is not being run by
+		 * root.  This keeps people from modifying setuid and setgid
+		 * binaries.
+		 */
+		ret = file_remove_privs(file_out);
+		if (ret)
+			return ret;
+	}
+
 	return 1;
 }
 EXPORT_SYMBOL(generic_remap_file_range_prep);

fs/xfs/xfs_reflink.c

@@ -1372,29 +1372,6 @@ xfs_reflink_remap_prep(
 	truncate_inode_pages_range(&inode_out->i_data, pos_out,
 				   PAGE_ALIGN(pos_out + *len) - 1);
 
-	/* If we're altering the file contents... */
-	if (!(remap_flags & REMAP_FILE_DEDUP)) {
-		/*
-		 * ...update the timestamps (which will grab the ilock again
-		 * from xfs_fs_dirty_inode, so we have to call it before we
-		 * take the ilock).
-		 */
-		if (!(file_out->f_mode & FMODE_NOCMTIME)) {
-			ret = file_update_time(file_out);
-			if (ret)
-				goto out_unlock;
-		}
-
-		/*
-		 * ...clear the security bits if the process is not being run
-		 * by root.  This keeps people from modifying setuid and setgid
-		 * binaries.
-		 */
-		ret = file_remove_privs(file_out);
-		if (ret)
-			goto out_unlock;
-	}
-
 	return 1;
 out_unlock:
 	xfs_reflink_remap_unlock(file_in, file_out);