allow root in container to copy namespaces (v3)

Quoting Eric W. Biederman (ebiederm@xmission.com):
> Serge Hallyn <serge@hallyn.com> writes:
>
> > From: Serge E. Hallyn <serge.hallyn@canonical.com>
> >
> > Othewise nested containers with user namespaces won't be possible.
> >
> > It's true that user namespaces are not yet fully isolated, but for
> > that same reason there are far worse things that root in a child
> > user ns can do.  Spawning a child user ns is not in itself bad.
> >
> > This patch also allows setns for root in a container:
> > @Eric Biederman: are there gotchas in allowing setns from child
> > userns?
>
> Yes.  We need to ensure that the target namespaces are namespaces
> that have been created in from user_namespace or from a child of this
> user_namespace.
>
> Aka we need to ensure that we have CAP_SYS_ADMIN for the new namespace.

[New patch below]

Othewise nested containers with user namespaces won't be possible.

It's true that user namespaces are not yet fully isolated, but for
that same reason there are far worse things that root in a child
user ns can do.  Spawning a child user ns is not in itself bad.

This patch also allows setns for root in a container:
@Eric Biederman: are there gotchas in allowing setns from child
userns?

Changelog:
  Jul 29: setns: target capability check for setns
          When changing to another namespace, make sure that we have
          the CAP_SYS_ADMIN capability targeted at the user namespace
          owning the new ns.

Signed-off-by: Serge E. Hallyn <serge.hallyn@canonical.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>

5 files changed, 13 insertions, 7 deletions

diff --git a/ipc/namespace.c b/ipc/namespace.c
index ce0a647869b1e..f527e499aa534 100644
--- a/ipc/namespace.c
+++ b/ipc/namespace.c
@@ -163,6 +163,9 @@ static void ipcns_put(void *ns)
 
 static int ipcns_install(struct nsproxy *nsproxy, void *ns)
 {
+	struct ipc_namespace *newns = ns;
+	if (!ns_capable(newns->user_ns, CAP_SYS_ADMIN))
+		return -1;
 	/* Ditch state from the old ipc namespace */
 	exit_sem(current);
 	put_ipc_ns(nsproxy->ipc_ns);
diff --git a/kernel/fork.c b/kernel/fork.c
index e7ceaca896094..f9fac70b3e419 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1488,8 +1488,8 @@ long do_fork(unsigned long clone_flags,
 		/* hopefully this check will go away when userns support is
 		 * complete
 		 */
-		if (!capable(CAP_SYS_ADMIN) || !capable(CAP_SETUID) ||
-				!capable(CAP_SETGID))
+		if (!nsown_capable(CAP_SYS_ADMIN) || !nsown_capable(CAP_SETUID) ||
+				!nsown_capable(CAP_SETGID))
 			return -EPERM;
 	}
 
diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
index 9aeab4b98c643..cadcee0529359 100644
--- a/kernel/nsproxy.c
+++ b/kernel/nsproxy.c
@@ -134,7 +134,7 @@ int copy_namespaces(unsigned long flags, struct task_struct *tsk)
 				CLONE_NEWPID | CLONE_NEWNET)))
 		return 0;
 
-	if (!capable(CAP_SYS_ADMIN)) {
+	if (!nsown_capable(CAP_SYS_ADMIN)) {
 		err = -EPERM;
 		goto out;
 	}
@@ -191,7 +191,7 @@ int unshare_nsproxy_namespaces(unsigned long unshare_flags,
 			       CLONE_NEWNET)))
 		return 0;
 
-	if (!capable(CAP_SYS_ADMIN))
+	if (!nsown_capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
 	*new_nsp = create_new_namespaces(unshare_flags, current,
@@ -241,9 +241,6 @@ SYSCALL_DEFINE2(setns, int, fd, int, nstype)
 	struct file *file;
 	int err;
 
-	if (!capable(CAP_SYS_ADMIN))
-		return -EPERM;
-
 	file = proc_ns_fget(fd);
 	if (IS_ERR(file))
 		return PTR_ERR(file);
diff --git a/kernel/utsname.c b/kernel/utsname.c
index bff131b9510a4..8f648ccc9f686 100644
--- a/kernel/utsname.c
+++ b/kernel/utsname.c
@@ -104,6 +104,9 @@ static void utsns_put(void *ns)
 
 static int utsns_install(struct nsproxy *nsproxy, void *ns)
 {
+	struct uts_namespace *newns = ns;
+	if (!ns_capable(newns->user_ns, CAP_SYS_ADMIN))
+		return -1;
 	get_uts_ns(ns);
 	put_uts_ns(nsproxy->uts_ns);
 	nsproxy->uts_ns = ns;
diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index 5bbdbf0d3664c..90c97f63365dc 100644
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -620,6 +620,9 @@ static void netns_put(void *ns)
 
 static int netns_install(struct nsproxy *nsproxy, void *ns)
 {
+	struct net *net = ns;
+	if (!ns_capable(net->user_ns, CAP_SYS_ADMIN))
+		return -1;
 	put_net(nsproxy->net_ns);
 	nsproxy->net_ns = get_net(ns);
 	return 0;