From 5ec2dd3a095442ec1a21d86042a4994f2ba24e63 Mon Sep 17 00:00:00 2001
Message-Id: <5ec2dd3a095442ec1a21d86042a4994f2ba24e63.1512651251.git.jan.steffens@gmail.com>
From: Serge Hallyn <serge.hallyn@canonical.com>
Date: Fri, 31 May 2013 19:12:12 +0100
Subject: [PATCH] add sysctl to disallow unprivileged CLONE_NEWUSER by default

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
[bwh: Remove unneeded binary sysctl bits]
Signed-off-by: Daniel Micay <danielmicay@gmail.com>
---
 kernel/fork.c           | 15 +++++++++++++++
 kernel/sysctl.c         | 12 ++++++++++++
 kernel/user_namespace.c |  3 +++
 3 files changed, 30 insertions(+)

diff --git a/kernel/fork.c b/kernel/fork.c
index 07cc743698d3668e..4011d68a8ff9305c 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -102,6 +102,11 @@
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/task.h>
+#ifdef CONFIG_USER_NS
+extern int unprivileged_userns_clone;
+#else
+#define unprivileged_userns_clone 0
+#endif
 
 /*
  * Minimum number of threads to boot the kernel
@@ -1555,6 +1560,10 @@ static __latent_entropy struct task_struct *copy_process(
 	if ((clone_flags & (CLONE_NEWUSER|CLONE_FS)) == (CLONE_NEWUSER|CLONE_FS))
 		return ERR_PTR(-EINVAL);
 
+	if ((clone_flags & CLONE_NEWUSER) && !unprivileged_userns_clone)
+		if (!capable(CAP_SYS_ADMIN))
+			return ERR_PTR(-EPERM);
+
 	/*
 	 * Thread groups must share signals as well, and detached threads
 	 * can only be started up within the thread group.
@@ -2348,6 +2357,12 @@ SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags)
 	if (unshare_flags & CLONE_NEWNS)
 		unshare_flags |= CLONE_FS;
 
+	if ((unshare_flags & CLONE_NEWUSER) && !unprivileged_userns_clone) {
+		err = -EPERM;
+		if (!capable(CAP_SYS_ADMIN))
+			goto bad_unshare_out;
+	}
+
 	err = check_unshare_flags(unshare_flags);
 	if (err)
 		goto bad_unshare_out;
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index b86520ed3fb60fbf..f7dab3760839f1a1 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -105,6 +105,9 @@ extern int core_uses_pid;
 extern char core_pattern[];
 extern unsigned int core_pipe_limit;
 #endif
+#ifdef CONFIG_USER_NS
+extern int unprivileged_userns_clone;
+#endif
 extern int pid_max;
 extern int pid_max_min, pid_max_max;
 extern int percpu_pagelist_fraction;
@@ -513,6 +516,15 @@ static struct ctl_table kern_table[] = {
 		.proc_handler	= proc_dointvec,
 	},
 #endif
+#ifdef CONFIG_USER_NS
+	{
+		.procname	= "unprivileged_userns_clone",
+		.data		= &unprivileged_userns_clone,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec,
+	},
+#endif
 #ifdef CONFIG_PROC_SYSCTL
 	{
 		.procname	= "tainted",
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index c490f1e4313b998a..dd03bd39d7bf194d 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -24,6 +24,9 @@
 #include <linux/projid.h>
 #include <linux/fs_struct.h>
 
+/* sysctl */
+int unprivileged_userns_clone;
+
 static struct kmem_cache *user_ns_cachep __read_mostly;
 static DEFINE_MUTEX(userns_state_mutex);
 
-- 
2.15.1

From b5202296055dd333db4425120d3f93ef4e6a0573 Mon Sep 17 00:00:00 2001
From: "Jan Alexander Steffens (heftig)" <jan.steffens@gmail.com>
Date: Thu, 7 Dec 2017 13:50:48 +0100
Subject: ZEN: Add CONFIG for unprivileged_userns_clone

This way our default behavior continues to match the vanilla kernel.
---
 init/Kconfig            | 16 ++++++++++++++++
 kernel/user_namespace.c |  4 ++++
 2 files changed, 20 insertions(+)

diff --git a/init/Kconfig b/init/Kconfig
index 4592bf7997c0..f3df02990aff 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1004,6 +1004,22 @@ config USER_NS
 
 	  If unsure, say N.
 
+config USER_NS_UNPRIVILEGED
+	bool "Allow unprivileged users to create namespaces"
+	default y
+	depends on USER_NS
+	help
+	  When disabled, unprivileged users will not be able to create
+	  new namespaces. Allowing users to create their own namespaces
+	  has been part of several recent local privilege escalation
+	  exploits, so if you need user namespaces but are
+	  paranoid^Wsecurity-conscious you want to disable this.
+
+	  This setting can be overridden at runtime via the
+	  kernel.unprivileged_userns_clone sysctl.
+
+	  If unsure, say Y.
+
 config PID_NS
 	bool "PID Namespaces"
 	default y
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 6b9dbc257e34..107b17f0d528 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -27,7 +27,11 @@
 #include <linux/sort.h>
 
 /* sysctl */
+#ifdef CONFIG_USER_NS_UNPRIVILEGED
+int unprivileged_userns_clone = 1;
+#else
 int unprivileged_userns_clone;
+#endif
 
 static struct kmem_cache *user_ns_cachep __read_mostly;
 static DEFINE_MUTEX(userns_state_mutex);
