From 29d4e22912c69936a503f521b8eff1b3d5dfd427 Mon Sep 17 00:00:00 2001 From: "Jan Alexander Steffens (heftig)" Date: Mon, 16 Sep 2019 04:53:20 +0200 Subject: [PATCH 1/4] 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 ef59c5c36cdb..aaad1e4a5772 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -1094,6 +1094,22 @@ 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 c9ba2b7bfef9..599349b67aca 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -106,6 +106,11 @@ #define CREATE_TRACE_POINTS #include +#ifdef CONFIG_USER_NS +extern int unprivileged_userns_clone; +#else +#define unprivileged_userns_clone 0 +#endif /* * Minimum number of threads to boot the kernel @@ -1844,6 +1849,10 @@ 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. @@ -2934,6 +2943,12 @@ 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 ad5b88a53c5a..8f00d26b7b59 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 #include +/* 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); -- 2.26.2