From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt0-f194.google.com ([209.85.216.194]:36313 "EHLO mail-qt0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752754AbcKONc2 (ORCPT ); Tue, 15 Nov 2016 08:32:28 -0500 Received: by mail-qt0-f194.google.com with SMTP id n34so8249636qtb.3 for ; Tue, 15 Nov 2016 05:32:27 -0800 (PST) Date: Tue, 15 Nov 2016 14:32:24 +0100 From: Johanna Abrahamsson To: Alexander Viro Cc: linux-fsdevel@vger.kernel.org Subject: [PATCH] vfs: Allow FS_USERNS_MOUNT filesystems to create inodes with unmapped uid/gids Message-ID: <20161115133221.GA23813@fedora-21-dvm> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Sender: linux-fsdevel-owner@vger.kernel.org List-ID: Fixes: 036d523641c6 ("vfs: Don't create inodes with a uid or gid unknown to the vfs") This fixes the bugzilla bug #183461 (https://bugzilla.kernel.org/show_bug.cgi?id=183461) "mkdir(2) returns EOVERFLOW on tmpfs in user namespace" that was introduced in the aforementioned commit. Since filesystems with the FS_USERNS_MOUNT flag (mainly tmpfs in this case) are safe to use within user namespaces they should be allowed to create inodes without checking whether their uid and gid has a mapping or not. I learned most of what I know about user namespaces while researching this bug, so there's a fair chance that I've misunderstood something. Feedback is greatly appreciated. Signed-off-by: Johanna Abrahamsson --- fs/namei.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/fs/namei.c b/fs/namei.c index 1669c93d..9e45e01 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -2816,10 +2816,12 @@ static inline int may_create(struct inode *dir, struct dentry *child) return -EEXIST; if (IS_DEADDIR(dir)) return -ENOENT; - s_user_ns = dir->i_sb->s_user_ns; - if (!kuid_has_mapping(s_user_ns, current_fsuid()) || - !kgid_has_mapping(s_user_ns, current_fsgid())) - return -EOVERFLOW; + if (!(dir->i_sb->s_type->fs_flags & FS_USERNS_MOUNT)) { + s_user_ns = dir->i_sb->s_user_ns; + if (!kuid_has_mapping(s_user_ns, current_fsuid()) || + !kgid_has_mapping(s_user_ns, current_fsgid())) + return -EOVERFLOW; + } return inode_permission(dir, MAY_WRITE | MAY_EXEC); } -- 2.1.4