From 8fa8a002546c42f061f070411ee50eb7e248ea0a Mon Sep 17 00:00:00 2001 From: Serge Hallyn Date: Tue, 5 Jan 2016 20:12:21 +0000 Subject: [PATCH] UBUNTU: SAUCE: add a sysctl to disable unprivileged user namespace unsharing It is turned on by default, but can be turned off if admins prefer or, more importantly, if a security vulnerability is found. The intent is to use this as mitigation so long as Ubuntu is on the cutting edge of enablement for things like unprivileged filesystem mounting. (This patch is tweaked from the one currently still in Debian sid, which in turn came from the patch we had in saucy) Signed-off-by: Serge Hallyn [bwh: Remove unneeded binary sysctl bits] Signed-off-by: Tim Gardner --- kernel/fork.c | 15 +++++++++++++++ kernel/sysctl.c | 12 ++++++++++++ kernel/user_namespace.c | 6 ++++++ 3 files changed, 33 insertions(+) diff --git a/kernel/fork.c b/kernel/fork.c index b7e9e57b71ea..db3a7d069397 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -100,6 +100,11 @@ #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 @@ -1539,6 +1544,10 @@ 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. @@ -2334,6 +2343,12 @@ 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 6648fbbb8157..a5ba626b848c 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -105,6 +105,9 @@ 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; @@ -512,6 +515,15 @@ 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 2f735cbe05e8..9708927ffa18 100644 --- a/kernel/user_namespace.c +++ b/kernel/user_namespace.c @@ -24,6 +24,12 @@ #include #include +/* + * sysctl determining whether unprivileged users may unshare a new + * userns. Allowed by default + */ +int unprivileged_userns_clone = 1; + static struct kmem_cache *user_ns_cachep __read_mostly; static DEFINE_MUTEX(userns_state_mutex); -- 2.39.5