From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1945933Ab2LNXaS (ORCPT ); Fri, 14 Dec 2012 18:30:18 -0500 Received: from 50-56-35-84.static.cloud-ips.com ([50.56.35.84]:58686 "EHLO mail.hallyn.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932763Ab2LNXaP (ORCPT ); Fri, 14 Dec 2012 18:30:15 -0500 Date: Fri, 14 Dec 2012 23:35:24 +0000 From: "Serge E. Hallyn" To: "Eric W. Biederman" Cc: Linux Containers , linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, "Serge E. Hallyn" , Andy Lutomirski , David Howells Subject: Re: [PATCH 2/4] userns: Require CAP_SYS_ADMIN for most uses of setns. Message-ID: <20121214233524.GA13659@mail.hallyn.com> References: <87txroxpgq.fsf@xmission.com> <87hanoxpdh.fsf@xmission.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87hanoxpdh.fsf@xmission.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Quoting Eric W. Biederman (ebiederm@xmission.com): > > Andy Lutomirski found a nasty little bug in > the permissions of setns. With unprivileged user namespaces it > became possible to create new namespaces without privilege. > > However the setns calls were relaxed to only require CAP_SYS_ADMIN in > the user nameapce of the targed namespace. > > Which made the following nasty sequence possible. > > pid = clone(CLONE_NEWUSER | CLONE_NEWNS); > if (pid == 0) { /* child */ > system("mount --bind /home/me/passwd /etc/passwd"); > } > else if (pid != 0) { /* parent */ > char path[PATH_MAX]; > snprintf(path, sizeof(path), "/proc/%u/ns/mnt"); > fd = open(path, O_RDONLY); > setns(fd, 0); > system("su -"); > } > > Prevent this possibility by requiring CAP_SYS_ADMIN > in the current user namespace when joing all but the user namespace. > > Signed-off-by: "Eric W. Biederman" Acked-by: Serge Hallyn > --- > fs/namespace.c | 3 ++- > ipc/namespace.c | 3 ++- > kernel/pid_namespace.c | 3 ++- > kernel/utsname.c | 3 ++- > net/core/net_namespace.c | 3 ++- > 5 files changed, 10 insertions(+), 5 deletions(-) > > diff --git a/fs/namespace.c b/fs/namespace.c > index c1bbe86..398a50f 100644 > --- a/fs/namespace.c > +++ b/fs/namespace.c > @@ -2781,7 +2781,8 @@ static int mntns_install(struct nsproxy *nsproxy, void *ns) > struct path root; > > if (!ns_capable(mnt_ns->user_ns, CAP_SYS_ADMIN) || > - !nsown_capable(CAP_SYS_CHROOT)) > + !nsown_capable(CAP_SYS_CHROOT) || > + !nsown_capable(CAP_SYS_ADMIN)) > return -EPERM; > > if (fs->users != 1) > diff --git a/ipc/namespace.c b/ipc/namespace.c > index cf3386a..7c1fa45 100644 > --- a/ipc/namespace.c > +++ b/ipc/namespace.c > @@ -170,7 +170,8 @@ static void ipcns_put(void *ns) > static int ipcns_install(struct nsproxy *nsproxy, void *new) > { > struct ipc_namespace *ns = new; > - if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN)) > + if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN) || > + !nsown_capable(CAP_SYS_ADMIN)) > return -EPERM; > > /* Ditch state from the old ipc namespace */ > diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c > index 560da0d..fdbd0cd 100644 > --- a/kernel/pid_namespace.c > +++ b/kernel/pid_namespace.c > @@ -325,7 +325,8 @@ static int pidns_install(struct nsproxy *nsproxy, void *ns) > struct pid_namespace *active = task_active_pid_ns(current); > struct pid_namespace *ancestor, *new = ns; > > - if (!ns_capable(new->user_ns, CAP_SYS_ADMIN)) > + if (!ns_capable(new->user_ns, CAP_SYS_ADMIN) || > + !nsown_capable(CAP_SYS_ADMIN)) > return -EPERM; > > /* > diff --git a/kernel/utsname.c b/kernel/utsname.c > index f6336d5..08b197e 100644 > --- a/kernel/utsname.c > +++ b/kernel/utsname.c > @@ -113,7 +113,8 @@ static int utsns_install(struct nsproxy *nsproxy, void *new) > { > struct uts_namespace *ns = new; > > - if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN)) > + if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN) || > + !nsown_capable(CAP_SYS_ADMIN)) > return -EPERM; > > get_uts_ns(ns); > diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c > index 2e9a313..8acce01 100644 > --- a/net/core/net_namespace.c > +++ b/net/core/net_namespace.c > @@ -649,7 +649,8 @@ static int netns_install(struct nsproxy *nsproxy, void *ns) > { > struct net *net = ns; > > - if (!ns_capable(net->user_ns, CAP_SYS_ADMIN)) > + if (!ns_capable(net->user_ns, CAP_SYS_ADMIN) || > + !nsown_capable(CAP_SYS_ADMIN)) > return -EPERM; > > put_net(nsproxy->net_ns); > -- > 1.7.5.4