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From a8d736bad70d4062a14c29bdcbed71bef7b575f5 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 01/15] ZEN: Add sysctl and CONFIG to disallow unprivileged
CLONE_NEWUSER
Our default behavior continues to match the vanilla kernel.
---
init/Kconfig | 16 ++++++++++++++++
kernel/fork.c | 15 +++++++++++++++
kernel/sysctl.c | 12 ++++++++++++
kernel/user_namespace.c | 7 +++++++
4 files changed, 50 insertions(+)
diff --git a/init/Kconfig b/init/Kconfig
index b4daad2bac23..362f82c5ec07 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1118,6 +1118,22 @@ 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 755d8160e001..ed909f8050b2 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -106,6 +106,11 @@
#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
@@ -1779,6 +1784,10 @@ 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.
@@ -2836,6 +2845,12 @@ 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 70665934d53e..9797869ed829 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -110,6 +110,9 @@ 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;
@@ -546,6 +549,15 @@ 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 8eadadc478f9..c36ecd19562c 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);
--
2.25.0
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