btrfs: disable various operations on encrypted inodes

Initially, only normal data extents will be encrypted. This change
forbids various other bits:

- allows reflinking only if both inodes have the same encryption status
- disable inline data on encrypted inodes

Note: The patch was taken from v5 of fscrypt patchset
(https://lore.kernel.org/linux-btrfs/cover.1706116485.git.josef@toxicpanda.com/)
which was handled over time by various people: Omar Sandoval, Sweet Tea
Dorminy, Josef Bacik.

Signed-off-by: Omar Sandoval <osandov@osandov.com>
Signed-off-by: Daniel Vacek <neelx@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
[ add note ]
Signed-off-by: David Sterba <dsterba@suse.com>

Author: osandov

fs/btrfs/inode.c

@@ -592,6 +592,10 @@ static bool can_cow_file_range_inline(struct btrfs_inode *inode,
 	if (size < i_size_read(&inode->vfs_inode))
 		return false;
 
+	/* Encrypted file cannot be inlined. */
+	if (IS_ENCRYPTED(&inode->vfs_inode))
+		return false;
+
 	return true;
 }
 

fs/btrfs/reflink.c

@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 
 #include <linux/blkdev.h>
+#include <linux/fscrypt.h>
 #include <linux/iversion.h>
 #include "ctree.h"
 #include "fs.h"
@@ -789,6 +790,10 @@ static int btrfs_remap_file_range_prep(struct file *file_in, loff_t pos_in,
 		ASSERT(inode_in->vfs_inode.i_sb == inode_out->vfs_inode.i_sb);
 	}
 
+	/* Can only reflink encrypted files if both files are encrypted. */
+	if (IS_ENCRYPTED(&inode_in->vfs_inode) != IS_ENCRYPTED(&inode_out->vfs_inode))
+		return -EINVAL;
+
 	/* Don't make the dst file partly checksummed */
 	if ((inode_in->flags & BTRFS_INODE_NODATASUM) !=
 	    (inode_out->flags & BTRFS_INODE_NODATASUM)) {