ceph: send alternate_name in MClientRequest

In the event that we have a filename longer than CEPH_NOHASH_NAME_MAX,
we'll need to hash the tail of the filename. The client however will
still need to know the full name of the file if it has a key.

To support this, the MClientRequest field has grown a new alternate_name
field that we populate with the full (binary) crypttext of the filename.
This is then transmitted to the clients in readdir or traces as part of
the dentry lease.

Add support for populating this field when the filenames are very long.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Xiubo Li <xiubli@redhat.com>
Reviewed-and-tested-by: Luís Henriques <lhenriques@suse.de>
Reviewed-by: Milind Changire <mchangir@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/mds_client.c

@@ -1027,6 +1027,7 @@ void ceph_mdsc_release_request(struct kref *kref)
 	if (req->r_pagelist)
 		ceph_pagelist_release(req->r_pagelist);
 	kfree(req->r_fscrypt_auth);
+	kfree(req->r_altname);
 	put_request_session(req);
 	ceph_unreserve_caps(req->r_mdsc, &req->r_caps_reservation);
 	WARN_ON_ONCE(!list_empty(&req->r_wait));
@@ -2435,6 +2436,64 @@ static inline  u64 __get_oldest_tid(struct ceph_mds_client *mdsc)
 	return mdsc->oldest_tid;
 }
 
+#if IS_ENABLED(CONFIG_FS_ENCRYPTION)
+static u8 *get_fscrypt_altname(const struct ceph_mds_request *req, u32 *plen)
+{
+	struct inode *dir = req->r_parent;
+	struct dentry *dentry = req->r_dentry;
+	u8 *cryptbuf = NULL;
+	u32 len = 0;
+	int ret = 0;
+
+	/* only encode if we have parent and dentry */
+	if (!dir || !dentry)
+		goto success;
+
+	/* No-op unless this is encrypted */
+	if (!IS_ENCRYPTED(dir))
+		goto success;
+
+	ret = __fscrypt_prepare_readdir(dir);
+	if (ret)
+		return ERR_PTR(ret);
+
+	/* No key? Just ignore it. */
+	if (!fscrypt_has_encryption_key(dir))
+		goto success;
+
+	if (!fscrypt_fname_encrypted_size(dir, dentry->d_name.len, NAME_MAX,
+					  &len)) {
+		WARN_ON_ONCE(1);
+		return ERR_PTR(-ENAMETOOLONG);
+	}
+
+	/* No need to append altname if name is short enough */
+	if (len <= CEPH_NOHASH_NAME_MAX) {
+		len = 0;
+		goto success;
+	}
+
+	cryptbuf = kmalloc(len, GFP_KERNEL);
+	if (!cryptbuf)
+		return ERR_PTR(-ENOMEM);
+
+	ret = fscrypt_fname_encrypt(dir, &dentry->d_name, cryptbuf, len);
+	if (ret) {
+		kfree(cryptbuf);
+		return ERR_PTR(ret);
+	}
+success:
+	*plen = len;
+	return cryptbuf;
+}
+#else
+static u8 *get_fscrypt_altname(const struct ceph_mds_request *req, u32 *plen)
+{
+	*plen = 0;
+	return NULL;
+}
+#endif
+
 /**
  * ceph_mdsc_build_path - build a path string to a given dentry
  * @dentry: dentry to which path should be built
@@ -2662,14 +2721,15 @@ static void encode_mclientrequest_tail(void **p,
 	ceph_encode_timespec64(&ts, &req->r_stamp);
 	ceph_encode_copy(p, &ts, sizeof(ts));
 
-	/* gid_list */
+	/* v4: gid_list */
 	ceph_encode_32(p, req->r_cred->group_info->ngroups);
 	for (i = 0; i < req->r_cred->group_info->ngroups; i++)
 		ceph_encode_64(p, from_kgid(&init_user_ns,
 					    req->r_cred->group_info->gid[i]));
 
-	/* v5: altname (TODO: skip for now) */
+	/* v5: altname */
-	ceph_encode_32(p, 0);
+	ceph_encode_32(p, req->r_altname_len);
+	ceph_encode_copy(p, req->r_altname, req->r_altname_len);
 
 	/* v6: fscrypt_auth and fscrypt_file */
 	if (req->r_fscrypt_auth) {
@@ -2729,7 +2789,13 @@ static struct ceph_msg *create_request_message(struct ceph_mds_session *session,
 		goto out_free1;
 	}
 
-	/* head */
+	req->r_altname = get_fscrypt_altname(req, &req->r_altname_len);
+	if (IS_ERR(req->r_altname)) {
+		msg = ERR_CAST(req->r_altname);
+		req->r_altname = NULL;
+		goto out_free2;
+	}
+
 	len = legacy ? sizeof(*head) : sizeof(struct ceph_mds_request_head);
 
 	/* filepaths */
@@ -2755,7 +2821,7 @@ static struct ceph_msg *create_request_message(struct ceph_mds_session *session,
 	len += sizeof(u32) + (sizeof(u64) * req->r_cred->group_info->ngroups);
 
 	/* alternate name */
-	len += sizeof(u32);	// TODO
+	len += sizeof(u32) + req->r_altname_len;
 
 	/* fscrypt_auth */
 	len += sizeof(u32); // fscrypt_auth

fs/ceph/mds_client.h

@@ -285,6 +285,9 @@ struct ceph_mds_request {
 
 	struct ceph_fscrypt_auth *r_fscrypt_auth;
 
+	u8 *r_altname;		    /* fscrypt binary crypttext for long filenames */
+	u32 r_altname_len;	    /* length of r_altname */
+
 	int r_fmode;        /* file mode, if expecting cap */
 	int r_request_release_offset;
 	const struct cred *r_cred;