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From 9baf57b4c2d9348bd5adecbb893870d1d79fade1 Mon Sep 17 00:00:00 2001
From: "Jan Alexander Steffens (heftig)" <jan.steffens@gmail.com>
Date: Mon, 16 Sep 2019 04:53:20 +0200
Subject: [PATCH 1/2] ZEN: Add sysctl and CONFIG to disallow unprivileged
CLONE_NEWUSER
Our default behavior continues to match the vanilla kernel.
---
include/linux/user_namespace.h | 4 ++++
init/Kconfig | 16 ++++++++++++++++
kernel/fork.c | 14 ++++++++++++++
kernel/sysctl.c | 12 ++++++++++++
kernel/user_namespace.c | 7 +++++++
5 files changed, 53 insertions(+)
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index 33a4240e6a6f..82213f9c4c17 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -139,6 +139,8 @@ static inline void set_rlimit_ucount_max(struct user_namespace *ns,
#ifdef CONFIG_USER_NS
+extern int unprivileged_userns_clone;
+
static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
{
if (ns)
@@ -172,6 +174,8 @@ extern bool current_in_userns(const struct user_namespace *target_ns);
struct ns_common *ns_get_owner(struct ns_common *ns);
#else
+#define unprivileged_userns_clone 0
+
static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
{
return &init_user_ns;
diff --git a/init/Kconfig b/init/Kconfig
index b19e2eeaae80..2c2e01d76076 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1240,6 +1240,22 @@ 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/fork.c b/kernel/fork.c
index 0d8abfb9e0f4..bd7c215e315f 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -99,6 +99,10 @@
#include <linux/bpf.h>
#include <linux/sched/mm.h>
+#ifdef CONFIG_USER_NS
+#include <linux/user_namespace.h>
+#endif
+
#include <asm/pgalloc.h>
#include <linux/uaccess.h>
#include <asm/mmu_context.h>
@@ -1992,6 +1996,10 @@ 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.
@@ -3128,6 +3136,12 @@ int ksys_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 830aaf8ca08e..af4c0806bd8e 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -91,6 +91,9 @@
#if defined(CONFIG_PROVE_LOCKING) || defined(CONFIG_LOCK_STAT)
#include <linux/lockdep.h>
#endif
+#ifdef CONFIG_USER_NS
+#include <linux/user_namespace.h>
+#endif
#if defined(CONFIG_SYSCTL)
@@ -1803,6 +1806,15 @@ static struct ctl_table kern_table[] = {
.mode = 0644,
.proc_handler = proc_dointvec,
},
+#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 5481ba44a8d6..423ab2563ad7 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -21,6 +21,13 @@
#include <linux/bsearch.h>
#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);
--
2.36.1
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