From 5ec2dd3a095442ec1a21d86042a4994f2ba24e63 Mon Sep 17 00:00:00 2001 Message-Id: <5ec2dd3a095442ec1a21d86042a4994f2ba24e63.1512651251.git.jan.steffens@gmail.com> From: Serge Hallyn Date: Fri, 31 May 2013 19:12:12 +0100 Subject: [PATCH] add sysctl to disallow unprivileged CLONE_NEWUSER by default Signed-off-by: Serge Hallyn [bwh: Remove unneeded binary sysctl bits] Signed-off-by: Daniel Micay --- kernel/fork.c | 15 +++++++++++++++ kernel/sysctl.c | 12 ++++++++++++ kernel/user_namespace.c | 3 +++ 3 files changed, 30 insertions(+) diff --git a/kernel/fork.c b/kernel/fork.c index 07cc743698d3668e..4011d68a8ff9305c 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -102,6 +102,11 @@ #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 @@ -1555,6 +1560,10 @@ 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. @@ -2348,6 +2357,12 @@ SYSCALL_DEFINE1(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 b86520ed3fb60fbf..f7dab3760839f1a1 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -105,6 +105,9 @@ extern int core_uses_pid; #if defined(CONFIG_SYSCTL) +#ifdef CONFIG_USER_NS +extern int unprivileged_userns_clone; +#endif /* Constants used for minimum and maximum */ #ifdef CONFIG_LOCKUP_DETECTOR static int sixty = 60; @@ -513,6 +516,15 @@ 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 c490f1e4313b998a..dd03bd39d7bf194d 100644 --- a/kernel/user_namespace.c +++ b/kernel/user_namespace.c @@ -24,6 +24,9 @@ #include #include +/* sysctl */ +int unprivileged_userns_clone; + static struct kmem_cache *user_ns_cachep __read_mostly; static DEFINE_MUTEX(userns_state_mutex); -- 2.15.1 From b5202296055dd333db4425120d3f93ef4e6a0573 Mon Sep 17 00:00:00 2001 From: "Jan Alexander Steffens (heftig)" Date: Thu, 7 Dec 2017 13:50:48 +0100 Subject: ZEN: Add CONFIG for unprivileged_userns_clone This way our default behavior continues to match the vanilla kernel. --- init/Kconfig | 16 ++++++++++++++++ kernel/user_namespace.c | 4 ++++ 2 files changed, 20 insertions(+) diff --git a/init/Kconfig b/init/Kconfig index 4592bf7997c0..f3df02990aff 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -1004,6 +1004,22 @@ 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/user_namespace.c b/kernel/user_namespace.c index 6b9dbc257e34..107b17f0d528 100644 --- a/kernel/user_namespace.c +++ b/kernel/user_namespace.c @@ -27,7 +27,11 @@ #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);