ceph: create symlinks with encrypted and base64-encoded targets

When creating symlinks in encrypted directories, encrypt and
base64-encode the target with the new inode's key before sending to the
MDS.

When filling a symlinked inode, base64-decode it into a buffer that
we'll keep in ci->i_symlink. When get_link is called, decrypt the buffer
into a new one that will hang off i_link.

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>

1 files changed, 49 insertions, 5 deletions

diff --git a/fs/ceph/dir.c b/fs/ceph/dir.c
index ee5c8b9c8630..7e064c024d2a 100644
--- a/fs/ceph/dir.c
+++ b/fs/ceph/dir.c
@@ -948,6 +948,43 @@ static int ceph_create(struct mnt_idmap *idmap, struct inode *dir,
 	return ceph_mknod(idmap, dir, dentry, mode, 0);
 }
 
+#if IS_ENABLED(CONFIG_FS_ENCRYPTION)
+static int prep_encrypted_symlink_target(struct ceph_mds_request *req,
+					 const char *dest)
+{
+	int err;
+	int len = strlen(dest);
+	struct fscrypt_str osd_link = FSTR_INIT(NULL, 0);
+
+	err = fscrypt_prepare_symlink(req->r_parent, dest, len, PATH_MAX,
+				      &osd_link);
+	if (err)
+		goto out;
+
+	err = fscrypt_encrypt_symlink(req->r_new_inode, dest, len, &osd_link);
+	if (err)
+		goto out;
+
+	req->r_path2 = kmalloc(CEPH_BASE64_CHARS(osd_link.len) + 1, GFP_KERNEL);
+	if (!req->r_path2) {
+		err = -ENOMEM;
+		goto out;
+	}
+
+	len = ceph_base64_encode(osd_link.name, osd_link.len, req->r_path2);
+	req->r_path2[len] = '\0';
+out:
+	fscrypt_fname_free_buffer(&osd_link);
+	return err;
+}
+#else
+static int prep_encrypted_symlink_target(struct ceph_mds_request *req,
+					 const char *dest)
+{
+	return -EOPNOTSUPP;
+}
+#endif
+
 static int ceph_symlink(struct mnt_idmap *idmap, struct inode *dir,
 			struct dentry *dentry, const char *dest)
 {
@@ -983,14 +1020,21 @@ static int ceph_symlink(struct mnt_idmap *idmap, struct inode *dir,
 		goto out_req;
 	}
 
-	req->r_path2 = kstrdup(dest, GFP_KERNEL);
-	if (!req->r_path2) {
-		err = -ENOMEM;
-		goto out_req;
-	}
 	req->r_parent = dir;
 	ihold(dir);
 
+	if (IS_ENCRYPTED(req->r_new_inode)) {
+		err = prep_encrypted_symlink_target(req, dest);
+		if (err)
+			goto out_req;
+	} else {
+		req->r_path2 = kstrdup(dest, GFP_KERNEL);
+		if (!req->r_path2) {
+			err = -ENOMEM;
+			goto out_req;
+		}
+	}
+
 	set_bit(CEPH_MDS_R_PARENT_LOCKED, &req->r_req_flags);
 	req->r_dentry = dget(dentry);
 	req->r_num_caps = 2;