1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
|
From f3564199e5416a4b2e98190ac37c1986aba049ae 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 1/3] 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 6030a8235..60b7fe5fa 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -156,6 +156,8 @@ static inline void set_userns_rlimit_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)
@@ -189,6 +191,8 @@ 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 5783a0b87..5ea911147 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1265,6 +1265,22 @@ 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 6b97fb2ac..003de4829 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -105,6 +105,10 @@
#include <uapi/linux/pidfd.h>
#include <linux/pidfs.h>
+#ifdef CONFIG_USER_NS
+#include <linux/user_namespace.h>
+#endif
+
#include <asm/pgalloc.h>
#include <linux/uaccess.h>
#include <asm/mmu_context.h>
@@ -2135,6 +2139,10 @@ __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.
@@ -3283,6 +3291,12 @@ 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 79e6cb1d5..676e89dc3 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -80,6 +80,9 @@
#ifdef CONFIG_RT_MUTEXES
#include <linux/rtmutex.h>
#endif
+#ifdef CONFIG_USER_NS
+#include <linux/user_namespace.h>
+#endif
/* shared constants to be used in various sysctls */
const int sysctl_vals[] = { 0, 1, 2, 3, 4, 100, 200, 1000, 3000, INT_MAX, 65535, -1 };
@@ -1618,6 +1621,15 @@ 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 0b0b95418..c4b835b91 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -22,6 +22,13 @@
#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 __ro_after_init;
static DEFINE_MUTEX(userns_state_mutex);
--
2.47.0
|