154 lines
4.4 KiB
Diff
154 lines
4.4 KiB
Diff
From 1ed48c405ba85328bae25d2f393700ba715a2f81 Mon Sep 17 00:00:00 2001
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From: "Jan Alexander Steffens (heftig)" <jan.steffens@gmail.com>
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Date: Mon, 16 Sep 2019 04:53:20 +0200
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Subject: [PATCH 1/2] ZEN: Add sysctl and CONFIG to disallow unprivileged
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CLONE_NEWUSER
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Our default behavior continues to match the vanilla kernel.
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---
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include/linux/user_namespace.h | 4 ++++
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init/Kconfig | 16 ++++++++++++++++
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kernel/fork.c | 14 ++++++++++++++
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kernel/sysctl.c | 12 ++++++++++++
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kernel/user_namespace.c | 7 +++++++
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5 files changed, 53 insertions(+)
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diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
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index f6c5f784be5a..07d194f23587 100644
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--- a/include/linux/user_namespace.h
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+++ b/include/linux/user_namespace.h
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@@ -108,6 +108,8 @@ void dec_ucount(struct ucounts *ucounts, enum ucount_type type);
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#ifdef CONFIG_USER_NS
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+extern int unprivileged_userns_clone;
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+
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static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
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{
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if (ns)
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@@ -141,6 +143,8 @@ extern bool current_in_userns(const struct user_namespace *target_ns);
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struct ns_common *ns_get_owner(struct ns_common *ns);
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#else
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+#define unprivileged_userns_clone 0
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+
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static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
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{
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return &init_user_ns;
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diff --git a/init/Kconfig b/init/Kconfig
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index 5f5c776ef192..afd708ed0241 100644
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--- a/init/Kconfig
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+++ b/init/Kconfig
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@@ -1177,6 +1177,22 @@ config USER_NS
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If unsure, say N.
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+config USER_NS_UNPRIVILEGED
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+ bool "Allow unprivileged users to create namespaces"
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+ default y
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+ depends on USER_NS
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+ help
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+ When disabled, unprivileged users will not be able to create
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+ new namespaces. Allowing users to create their own namespaces
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+ has been part of several recent local privilege escalation
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+ exploits, so if you need user namespaces but are
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+ paranoid^Wsecurity-conscious you want to disable this.
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+
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+ This setting can be overridden at runtime via the
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+ kernel.unprivileged_userns_clone sysctl.
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+
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+ If unsure, say Y.
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+
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config PID_NS
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bool "PID Namespaces"
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default y
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diff --git a/kernel/fork.c b/kernel/fork.c
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index 426cd0c51f9e..e83a79860d58 100644
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--- a/kernel/fork.c
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+++ b/kernel/fork.c
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@@ -97,6 +97,10 @@
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#include <linux/scs.h>
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#include <linux/io_uring.h>
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+#ifdef CONFIG_USER_NS
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+#include <linux/user_namespace.h>
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+#endif
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+
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#include <asm/pgalloc.h>
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#include <linux/uaccess.h>
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#include <asm/mmu_context.h>
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@@ -1872,6 +1876,10 @@ static __latent_entropy struct task_struct *copy_process(
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if ((clone_flags & (CLONE_NEWUSER|CLONE_FS)) == (CLONE_NEWUSER|CLONE_FS))
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return ERR_PTR(-EINVAL);
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+ if ((clone_flags & CLONE_NEWUSER) && !unprivileged_userns_clone)
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+ if (!capable(CAP_SYS_ADMIN))
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+ return ERR_PTR(-EPERM);
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+
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/*
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* Thread groups must share signals as well, and detached threads
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* can only be started up within the thread group.
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@@ -2971,6 +2979,12 @@ int ksys_unshare(unsigned long unshare_flags)
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if (unshare_flags & CLONE_NEWNS)
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unshare_flags |= CLONE_FS;
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+ if ((unshare_flags & CLONE_NEWUSER) && !unprivileged_userns_clone) {
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+ err = -EPERM;
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+ if (!capable(CAP_SYS_ADMIN))
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+ goto bad_unshare_out;
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+ }
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+
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err = check_unshare_flags(unshare_flags);
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if (err)
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goto bad_unshare_out;
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diff --git a/kernel/sysctl.c b/kernel/sysctl.c
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index 62fbd09b5dc1..01192edd25f3 100644
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--- a/kernel/sysctl.c
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+++ b/kernel/sysctl.c
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@@ -103,6 +103,9 @@
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#ifdef CONFIG_LOCKUP_DETECTOR
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#include <linux/nmi.h>
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#endif
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+#ifdef CONFIG_USER_NS
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+#include <linux/user_namespace.h>
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+#endif
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#if defined(CONFIG_SYSCTL)
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@@ -1902,6 +1905,15 @@ static struct ctl_table kern_table[] = {
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.proc_handler = proc_dointvec,
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},
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#endif
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+#ifdef CONFIG_USER_NS
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+ {
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+ .procname = "unprivileged_userns_clone",
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+ .data = &unprivileged_userns_clone,
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+ .maxlen = sizeof(int),
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+ .mode = 0644,
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+ .proc_handler = proc_dointvec,
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+ },
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+#endif
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#ifdef CONFIG_PROC_SYSCTL
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{
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.procname = "tainted",
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diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
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index 9a4b980d695b..4388ca13ea3f 100644
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--- a/kernel/user_namespace.c
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+++ b/kernel/user_namespace.c
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@@ -21,6 +21,13 @@
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#include <linux/bsearch.h>
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#include <linux/sort.h>
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+/* sysctl */
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+#ifdef CONFIG_USER_NS_UNPRIVILEGED
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+int unprivileged_userns_clone = 1;
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+#else
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+int unprivileged_userns_clone;
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+#endif
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+
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static struct kmem_cache *user_ns_cachep __read_mostly;
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static DEFINE_MUTEX(userns_state_mutex);
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--
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2.31.1
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