ceph: fix up error handling with snapdirs

There are several warts in the snapdir error handling. The -EOPNOTSUPP
return in __snapfh_to_dentry is currently lost, and the call to
ceph_handle_snapdir is not currently checked at all.

Fix all of this up and eliminate a BUG_ON in ceph_get_snapdir. We can
handle that case with a warning and return an error.
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/ceph/dir.c

@@ -677,6 +677,8 @@ int ceph_handle_snapdir(struct ceph_mds_request *req,
 	    strcmp(dentry->d_name.name,
 		   fsc->mount_options->snapdir_name) == 0) {
 		struct inode *inode = ceph_get_snapdir(parent);
+		if (IS_ERR(inode))
+			return PTR_ERR(inode);
 		dout("ENOENT on snapdir %p '%pd', linking to snapdir %p\n",
 		     dentry, dentry, inode);
 		BUG_ON(!d_unhashed(dentry));

fs/ceph/export.c

@@ -248,9 +248,10 @@ static struct dentry *__snapfh_to_dentry(struct super_block *sb,
 			ihold(inode);
 		} else {
 			/* mds does not support lookup snapped inode */
-			err = -EOPNOTSUPP;
-			inode = NULL;
+			inode = ERR_PTR(-EOPNOTSUPP);
 		}
+	} else {
+		inode = ERR_PTR(-ESTALE);
 	}
 	ceph_mdsc_put_request(req);
 
@@ -261,8 +262,8 @@ static struct dentry *__snapfh_to_dentry(struct super_block *sb,
 		dout("snapfh_to_dentry %llx.%llx parent %llx hash %x err=%d",
 		      vino.ino, vino.snap, sfh->parent_ino, sfh->hash, err);
 	}
-	if (!inode)
-		return ERR_PTR(-ESTALE);
+	if (IS_ERR(inode))
+		return ERR_CAST(inode);
 	/* see comments in ceph_get_parent() */
 	return unlinked ? d_obtain_root(inode) : d_obtain_alias(inode);
 }

fs/ceph/inode.c

@@ -78,9 +78,21 @@ struct inode *ceph_get_snapdir(struct inode *parent)
 	struct inode *inode = ceph_get_inode(parent->i_sb, vino);
 	struct ceph_inode_info *ci = ceph_inode(inode);
 
-	BUG_ON(!S_ISDIR(parent->i_mode));
 	if (IS_ERR(inode))
 		return inode;
+
+	if (!S_ISDIR(parent->i_mode)) {
+		pr_warn_once("bad snapdir parent type (mode=0%o)\n",
+			     parent->i_mode);
+		return ERR_PTR(-ENOTDIR);
+	}
+
+	if (!(inode->i_state & I_NEW) && !S_ISDIR(inode->i_mode)) {
+		pr_warn_once("bad snapdir inode type (mode=0%o)\n",
+			     inode->i_mode);
+		return ERR_PTR(-ENOTDIR);
+	}
+
 	inode->i_mode = parent->i_mode;
 	inode->i_uid = parent->i_uid;
 	inode->i_gid = parent->i_gid;