132 lines
3.7 KiB
Diff
132 lines
3.7 KiB
Diff
From f4b254de5d2b75143dd7c225e58afb3f5ee3bae6 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] 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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init/Kconfig | 16 ++++++++++++++++
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kernel/fork.c | 15 +++++++++++++++
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kernel/sysctl.c | 12 ++++++++++++
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kernel/user_namespace.c | 7 +++++++
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4 files changed, 50 insertions(+)
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diff --git a/init/Kconfig b/init/Kconfig
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index 6db3e310a5e4..2dd7dd1b6b0d 100644
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--- a/init/Kconfig
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+++ b/init/Kconfig
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@@ -1083,6 +1083,22 @@ 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 9180f4416dba..a02f83b1d9b4 100644
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--- a/kernel/fork.c
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+++ b/kernel/fork.c
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@@ -106,6 +106,11 @@
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#define CREATE_TRACE_POINTS
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#include <trace/events/task.h>
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+#ifdef CONFIG_USER_NS
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+extern int unprivileged_userns_clone;
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+#else
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+#define unprivileged_userns_clone 0
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+#endif
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/*
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* Minimum number of threads to boot the kernel
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@@ -1779,6 +1784,10 @@ 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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@@ -2837,6 +2846,12 @@ 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 70665934d53e..9797869ed829 100644
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--- a/kernel/sysctl.c
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+++ b/kernel/sysctl.c
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@@ -110,6 +110,9 @@ extern int core_uses_pid;
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extern char core_pattern[];
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extern unsigned int core_pipe_limit;
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#endif
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+#ifdef CONFIG_USER_NS
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+extern int unprivileged_userns_clone;
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+#endif
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extern int pid_max;
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extern int pid_max_min, pid_max_max;
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extern int percpu_pagelist_fraction;
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@@ -546,6 +549,15 @@ 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 8eadadc478f9..c36ecd19562c 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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2.26.2
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