[fscrypt][RFC PATCH] ceph: don't allow changing layout on encrypted files/directories

[Luis Henriques]

Encryption is currently only supported on files/directories with layouts
where stripe_count=1.  Forbid changing layouts when encryption is involved.

Signed-off-by: Luis Henriques <lhenriques@xxxxxxx>
---
Hi!

While continuing looking into fscrypt, I realized we're not yet forbidding
different layouts on encrypted files.  This patch tries to do just that.

Regarding the setxattr, I've also made a change [1] to the MDS code so that it
also prevents layouts to be changed.  This should make the changes to
ceph_sync_setxattr() redundant, but in practice it doesn't because if we encrypt
a directory and immediately after that we change that directory layout, the MDS
wouldn't yet have received the fscrypt_auth for that inode.  So... yeah, an
alternative would be to propagate the fscrypt context immediately after
encrypting a directory.

[1] https://github.com/luis-henrix/ceph/commit/601488ae798ecfa5ec81677d1ced02f7dd42aa10

Cheers,
--
Luis

 fs/ceph/ioctl.c | 4 ++++
 fs/ceph/xattr.c | 6 ++++++
 2 files changed, 10 insertions(+)

diff --git a/fs/ceph/ioctl.c b/fs/ceph/ioctl.c
index 477ecc667aee..42abfc564301 100644
--- a/fs/ceph/ioctl.c
+++ b/fs/ceph/ioctl.c
@@ -294,6 +294,10 @@ static long ceph_set_encryption_policy(struct file *file, unsigned long arg)
 	struct inode *inode = file_inode(file);
 	struct ceph_inode_info *ci = ceph_inode(inode);
 
+	/* encrypted directories can't have striped layout */
+	if (ci->i_layout.stripe_count > 1)
+		return -EOPNOTSUPP;
+
 	ret = vet_mds_for_fscrypt(file);
 	if (ret)
 		return ret;
diff --git a/fs/ceph/xattr.c b/fs/ceph/xattr.c
index b175b3029dc0..7921cb34900c 100644
--- a/fs/ceph/xattr.c
+++ b/fs/ceph/xattr.c
@@ -1051,6 +1051,12 @@ static int ceph_sync_setxattr(struct inode *inode, const char *name,
 	int op = CEPH_MDS_OP_SETXATTR;
 	int err;
 
+	/* encrypted directories/files can't have their layout changed */
+	if (IS_ENCRYPTED(inode) &&
+	    (!strncmp(name, "ceph.file.layout", 16) ||
+	     !strncmp(name, "ceph.dir.layout", 15)))
+		return -EOPNOTSUPP;
+
 	if (size > 0) {
 		/* copy value into pagelist */
 		pagelist = ceph_pagelist_alloc(GFP_NOFS);

Cheers,
--
Luís