Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754786AbcCNFG1 (ORCPT ); Mon, 14 Mar 2016 01:06:27 -0400 Received: from mail.kernel.org ([198.145.29.136]:60533 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753842AbcCNFGV (ORCPT ); Mon, 14 Mar 2016 01:06:21 -0400 From: Andy Lutomirski To: Linux FS Devel , , "Eric W. Biederman" Cc: gnome-os-list@gnome.org, James Bottomley , Andy Lutomirski , Alexander Larsson , mclasen@redhat.com, Linux Containers Subject: [PATCH] devpts: Make ptmx be owned by the userns owner instead of userns-local 0 Date: Sun, 13 Mar 2016 22:06:15 -0700 Message-Id: X-Mailer: git-send-email 2.5.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2593 Lines: 75 We used to have ptmx be owned by the inner uid and gid 0. Change this: if the owner and group are both mapped but are not both 0, then use the owner instead. For container-style namespaces (LXC, etc), this should have no effect -- UID 0 is will either be the owner or will be unmapped. The important behavior change is for sandboxes: many sandboxes intentionally do not create an inner uid 0. Without this patch, mounting devpts in such a sandbox is awkward. With this patch, it will just work and ptmx will be owned by the namespace owner. Cc: Alexander Larsson Cc: mclasen@redhat.com Cc: "Eric W. Biederman" Cc: Linux Containers Signed-off-by: Andy Lutomirski --- fs/devpts/inode.c | 34 ++++++++++++++++++++++++++++++---- 1 file changed, 30 insertions(+), 4 deletions(-) diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c index 655f21f99160..d6fa2d1beee3 100644 --- a/fs/devpts/inode.c +++ b/fs/devpts/inode.c @@ -27,6 +27,7 @@ #include #include #include +#include #define DEVPTS_DEFAULT_MODE 0600 /* @@ -250,10 +251,35 @@ static int mknod_ptmx(struct super_block *sb) kuid_t root_uid; kgid_t root_gid; - root_uid = make_kuid(current_user_ns(), 0); - root_gid = make_kgid(current_user_ns(), 0); - if (!uid_valid(root_uid) || !gid_valid(root_gid)) - return -EINVAL; + /* + * For a new devpts instance, ptmx is owned by the creating user + * namespace's owner. Usually, that will be 0 as seen by the + * user namespace, but for unprivileged sandbox namespaces, + * there may not be a uid 0 or gid 0 at all. + */ + root_uid = current_user_ns()->owner; + root_gid = current_user_ns()->group; + + if (!uid_valid(root_uid) || !gid_valid(root_gid)) { + /* + * It's very unlikely for us to get here if the userns + * owner is not mapped, but it's possible -- we'd have + * to be running in the userns with capabilities granted + * by unshare or setns, since there is no inner + * privileged user. Nonetheless, this could happen, and + * we don't want ptmx to be owned by an unmapped user or + * group. + * + * If this happens fall back to historical behavior: + * try to have ptmx be owned by 0:0. + */ + root_uid = make_kuid(current_user_ns(), 0); + root_gid = make_kgid(current_user_ns(), 0); + + /* If this still doesn't work, give up. */ + if (!uid_valid(root_uid) || !gid_valid(root_gid)) + return -EINVAL; + } inode_lock(d_inode(root)); -- 2.5.0