ceph: add support for encrypted snapshot names

Since filenames in encrypted directories are encrypted and shown as
a base64-encoded string when the directory is locked, make snapshot
names show a similar behaviour.

When creating a snapshot, .snap directories for every subdirectory will
show the snapshot name in the "long format":

# mkdir .snap/my-snap
# ls my-dir/.snap/
_my-snap_1099511627782

Encrypted snapshots will need to be able to handle these by
encrypting/decrypting only the snapshot part of the string ('my-snap').

Also, since the MDS prevents snapshot names to be bigger than 240
characters it is necessary to adapt CEPH_NOHASH_NAME_MAX to accommodate
this extra limitation.

[ idryomov: drop const on !CONFIG_FS_ENCRYPTION branch too ]

Signed-off-by: Luís Henriques <[e-mail]>
Reviewed-by: Jeff Layton <[e-mail]>
Reviewed-by: Xiubo Li <[e-mail]>
Reviewed-by: Milind Changire <[e-mail]>
Signed-off-by: Ilya Dryomov <[e-mail]>

fs/ceph/crypto.c

···
 	swap(req->r_fscrypt_auth, as->fscrypt_auth);
 }
 
-int ceph_encode_encrypted_dname(const struct inode *parent,
-				struct qstr *d_name, char *buf)
+/*
+ * User-created snapshots can't start with '_'.  Snapshots that start with this
+ * character are special (hint: there aren't real snapshots) and use the
+ * following format:
+ *
+ *   _<SNAPSHOT-NAME>_<INODE-NUMBER>
+ *
+ * where:
+ *  - <SNAPSHOT-NAME> - the real snapshot name that may need to be decrypted,
+ *  - <INODE-NUMBER> - the inode number (in decimal) for the actual snapshot
+ *
+ * This function parses these snapshot names and returns the inode
+ * <INODE-NUMBER>.  'name_len' will also bet set with the <SNAPSHOT-NAME>
+ * length.
+ */
+static struct inode *parse_longname(const struct inode *parent,
+				    const char *name, int *name_len)
 {
+	struct inode *dir = NULL;
+	struct ceph_vino vino = { .snap = CEPH_NOSNAP };
+	char *inode_number;
+	char *name_end;
+	int orig_len = *name_len;
+	int ret = -EIO;
+
+	/* Skip initial '_' */
+	name++;
+	name_end = strrchr(name, '_');
+	if (!name_end) {
+		dout("Failed to parse long snapshot name: %s\n", name);
+		return ERR_PTR(-EIO);
+	}
+	*name_len = (name_end - name);
+	if (*name_len <= 0) {
+		pr_err("Failed to parse long snapshot name\n");
+		return ERR_PTR(-EIO);
+	}
+
+	/* Get the inode number */
+	inode_number = kmemdup_nul(name_end + 1,
+				   orig_len - *name_len - 2,
+				   GFP_KERNEL);
+	if (!inode_number)
+		return ERR_PTR(-ENOMEM);
+	ret = kstrtou64(inode_number, 10, &vino.ino);
+	if (ret) {
+		dout("Failed to parse inode number: %s\n", name);
+		dir = ERR_PTR(ret);
+		goto out;
+	}
+
+	/* And finally the inode */
+	dir = ceph_find_inode(parent->i_sb, vino);
+	if (!dir) {
+		/* This can happen if we're not mounting cephfs on the root */
+		dir = ceph_get_inode(parent->i_sb, vino, NULL);
+		if (!dir)
+			dir = ERR_PTR(-ENOENT);
+	}
+	if (IS_ERR(dir))
+		dout("Can't find inode %s (%s)\n", inode_number, name);
+
+out:
+	kfree(inode_number);
+	return dir;
+}
+
+int ceph_encode_encrypted_dname(struct inode *parent, struct qstr *d_name,
+				char *buf)
+{
+	struct inode *dir = parent;
+	struct qstr iname;
 	u32 len;
+	int name_len;
 	int elen;
 	int ret;
-	u8 *cryptbuf;
+	u8 *cryptbuf = NULL;
 
-	if (!fscrypt_has_encryption_key(parent)) {
+	iname.name = d_name->name;
+	name_len = d_name->len;
+
+	/* Handle the special case of snapshot names that start with '_' */
+	if ((ceph_snap(dir) == CEPH_SNAPDIR) && (name_len > 0) &&
+	    (iname.name[0] == '_')) {
+		dir = parse_longname(parent, iname.name, &name_len);
+		if (IS_ERR(dir))
+			return PTR_ERR(dir);
+		iname.name++; /* skip initial '_' */
+	}
+	iname.len = name_len;
+
+	if (!fscrypt_has_encryption_key(dir)) {
 		memcpy(buf, d_name->name, d_name->len);
-		return d_name->len;
+		elen = d_name->len;
+		goto out;
 	}
 
 	/*
···
 	 *
 	 * See: fscrypt_setup_filename
 	 */
-	if (!fscrypt_fname_encrypted_size(parent, d_name->len, NAME_MAX, &len))
-		return -ENAMETOOLONG;
+	if (!fscrypt_fname_encrypted_size(dir, iname.len, NAME_MAX, &len)) {
+		elen = -ENAMETOOLONG;
+		goto out;
+	}
 
 	/* Allocate a buffer appropriate to hold the result */
 	cryptbuf = kmalloc(len > CEPH_NOHASH_NAME_MAX ? NAME_MAX : len,
 			   GFP_KERNEL);
-	if (!cryptbuf)
-		return -ENOMEM;
+	if (!cryptbuf) {
+		elen = -ENOMEM;
+		goto out;
+	}
 
-	ret = fscrypt_fname_encrypt(parent, d_name, cryptbuf, len);
+	ret = fscrypt_fname_encrypt(dir, &iname, cryptbuf, len);
 	if (ret) {
-		kfree(cryptbuf);
-		return ret;
+		elen = ret;
+		goto out;
 	}
 
 	/* hash the end if the name is long enough */
···
 
 	/* base64 encode the encrypted name */
 	elen = ceph_base64_encode(cryptbuf, len, buf);
-	kfree(cryptbuf);
 	dout("base64-encoded ciphertext name = %.*s\n", elen, buf);
+
+	/* To understand the 240 limit, see CEPH_NOHASH_NAME_MAX comments */
+	WARN_ON(elen > 240);
+	if ((elen > 0) && (dir != parent)) {
+		char tmp_buf[NAME_MAX];
+
+		elen = snprintf(tmp_buf, sizeof(tmp_buf), "_%.*s_%ld",
+				elen, buf, dir->i_ino);
+		memcpy(buf, tmp_buf, elen);
+	}
+
+out:
+	kfree(cryptbuf);
+	if (dir != parent) {
+		if ((dir->i_state & I_NEW))
+			discard_new_inode(dir);
+		else
+			iput(dir);
+	}
 	return elen;
 }
 
-int ceph_encode_encrypted_fname(const struct inode *parent,
-				struct dentry *dentry, char *buf)
+int ceph_encode_encrypted_fname(struct inode *parent, struct dentry *dentry,
+				char *buf)
 {
 	WARN_ON_ONCE(!fscrypt_has_encryption_key(parent));
 
···
 int ceph_fname_to_usr(const struct ceph_fname *fname, struct fscrypt_str *tname,
 		      struct fscrypt_str *oname, bool *is_nokey)
 {
-	int ret;
+	struct inode *dir = fname->dir;
 	struct fscrypt_str _tname = FSTR_INIT(NULL, 0);
 	struct fscrypt_str iname;
-
-	if (!IS_ENCRYPTED(fname->dir)) {
-		oname->name = fname->name;
-		oname->len = fname->name_len;
-		return 0;
-	}
+	char *name = fname->name;
+	int name_len = fname->name_len;
+	int ret;
 
 	/* Sanity check that the resulting name will fit in the buffer */
 	if (fname->name_len > NAME_MAX || fname->ctext_len > NAME_MAX)
 		return -EIO;
 
-	ret = ceph_fscrypt_prepare_readdir(fname->dir);
-	if (ret < 0)
-		return ret;
+	/* Handle the special case of snapshot names that start with '_' */
+	if ((ceph_snap(dir) == CEPH_SNAPDIR) && (name_len > 0) &&
+	    (name[0] == '_')) {
+		dir = parse_longname(dir, name, &name_len);
+		if (IS_ERR(dir))
+			return PTR_ERR(dir);
+		name++; /* skip initial '_' */
+	}
+
+	if (!IS_ENCRYPTED(dir)) {
+		oname->name = fname->name;
+		oname->len = fname->name_len;
+		ret = 0;
+		goto out_inode;
+	}
+
+	ret = ceph_fscrypt_prepare_readdir(dir);
+	if (ret)
+		goto out_inode;
 
 	/*
 	 * Use the raw dentry name as sent by the MDS instead of
 	 * generating a nokey name via fscrypt.
 	 */
-	if (!fscrypt_has_encryption_key(fname->dir)) {
+	if (!fscrypt_has_encryption_key(dir)) {
 		if (fname->no_copy)
 			oname->name = fname->name;
 		else
···
 		oname->len = fname->name_len;
 		if (is_nokey)
 			*is_nokey = true;
-		return 0;
+		ret = 0;
+		goto out_inode;
 	}
 
 	if (fname->ctext_len == 0) {
···
 		if (!tname) {
 			ret = fscrypt_fname_alloc_buffer(NAME_MAX, &_tname);
 			if (ret)
-				return ret;
+				goto out_inode;
 			tname = &_tname;
 		}
 
-		declen = ceph_base64_decode(fname->name, fname->name_len,
-					    tname->name);
+		declen = ceph_base64_decode(name, name_len, tname->name);
 		if (declen <= 0) {
 			ret = -EIO;
 			goto out;
···
 		iname.len = fname->ctext_len;
 	}
 
-	ret = fscrypt_fname_disk_to_usr(fname->dir, 0, 0, &iname, oname);
+	ret = fscrypt_fname_disk_to_usr(dir, 0, 0, &iname, oname);
+	if (!ret && (dir != fname->dir)) {
+		char tmp_buf[CEPH_BASE64_CHARS(NAME_MAX)];
+
+		name_len = snprintf(tmp_buf, sizeof(tmp_buf), "_%.*s_%ld",
+				    oname->len, oname->name, dir->i_ino);
+		memcpy(oname->name, tmp_buf, name_len);
+		oname->len = name_len;
+	}
+
 out:
 	fscrypt_fname_free_buffer(&_tname);
+out_inode:
+	if ((dir != fname->dir) && !IS_ERR(dir)) {
+		if ((dir->i_state & I_NEW))
+			discard_new_inode(dir);
+		else
+			iput(dir);
+	}
 	return ret;
 }
 

fs/ceph/crypto.h

···
 				 struct ceph_acl_sec_ctx *as);
 void ceph_fscrypt_as_ctx_to_req(struct ceph_mds_request *req,
 				struct ceph_acl_sec_ctx *as);
-int ceph_encode_encrypted_dname(const struct inode *parent,
-				struct qstr *d_name, char *buf);
-int ceph_encode_encrypted_fname(const struct inode *parent,
-				struct dentry *dentry, char *buf);
+int ceph_encode_encrypted_dname(struct inode *parent, struct qstr *d_name,
+				char *buf);
+int ceph_encode_encrypted_fname(struct inode *parent, struct dentry *dentry,
+				char *buf);
 
 static inline int ceph_fname_alloc_buffer(struct inode *parent,
 					  struct fscrypt_str *fname)
···
 {
 }
 
-static inline int ceph_encode_encrypted_dname(const struct inode *parent,
+static inline int ceph_encode_encrypted_dname(struct inode *parent,
 					      struct qstr *d_name, char *buf)
 {
 	memcpy(buf, d_name->name, d_name->len);
 	return d_name->len;
 }
 
-static inline int ceph_encode_encrypted_fname(const struct inode *parent,
+static inline int ceph_encode_encrypted_fname(struct inode *parent,
 					      struct dentry *dentry, char *buf)
 {
 	return -EOPNOTSUPP;

fs/ceph/inode.c

···
 	if (err < 0)
 		goto out_err;
 
-	err = ceph_fscrypt_prepare_context(dir, inode, as_ctx);
-	if (err)
-		goto out_err;
+	/*
+	 * We'll skip setting fscrypt context for snapshots, leaving that for
+	 * the handle_reply().
+	 */
+	if (ceph_snap(dir) != CEPH_SNAPDIR) {
+		err = ceph_fscrypt_prepare_context(dir, inode, as_ctx);
+		if (err)
+			goto out_err;
+	}
 
 	return inode;
 out_err:
···
 	};
 	struct inode *inode = ceph_get_inode(parent->i_sb, vino, NULL);
 	struct ceph_inode_info *ci = ceph_inode(inode);
+	int ret = -ENOTDIR;
 
 	if (IS_ERR(inode))
 		return inode;
···
 	ci->i_rbytes = 0;
 	ci->i_btime = ceph_inode(parent)->i_btime;
 
+#ifdef CONFIG_FS_ENCRYPTION
+	/* if encrypted, just borrow fscrypt_auth from parent */
+	if (IS_ENCRYPTED(parent)) {
+		struct ceph_inode_info *pci = ceph_inode(parent);
+
+		ci->fscrypt_auth = kmemdup(pci->fscrypt_auth,
+					   pci->fscrypt_auth_len,
+					   GFP_KERNEL);
+		if (ci->fscrypt_auth) {
+			inode->i_flags |= S_ENCRYPTED;
+			ci->fscrypt_auth_len = pci->fscrypt_auth_len;
+		} else {
+			dout("Failed to alloc snapdir fscrypt_auth\n");
+			ret = -ENOMEM;
+			goto err;
+		}
+	}
+#endif
 	if (inode->i_state & I_NEW) {
 		inode->i_op = &ceph_snapdir_iops;
 		inode->i_fop = &ceph_snapdir_fops;
···
 		discard_new_inode(inode);
 	else
 		iput(inode);
-	return ERR_PTR(-ENOTDIR);
+	return ERR_PTR(ret);
 }
 
 const struct inode_operations ceph_file_iops = {