From d70cb56d43efddd10d4263f2af24f52fb81137b9 Mon Sep 17 00:00:00 2001 From: Serge Hallyn Date: Fri, 31 May 2013 19:12:12 +0100 Subject: [PATCH] add sysctl to disallow unprivileged CLONE_NEWUSER by default add sysctl to disallow unprivileged CLONE_NEWUSER by default This is a short-term patch. Unprivileged use of CLONE_NEWUSER is certainly an intended feature of user namespaces. However for at least saucy we want to make sure that, if any security issues are found, we have a fail-safe. Signed-off-by: Serge Hallyn [bwh: Remove unneeded binary sysctl bits] [bwh: Keep this sysctl, but change the default to enabled] --- kernel/fork.c | 16 ++++++++++++++++ kernel/sysctl.c | 13 +++++++++++++ kernel/user_namespace.c | 3 +++ 3 files changed, 32 insertions(+) diff --git a/kernel/fork.c b/kernel/fork.c index ca2ca3884f76..d9591a8a6ead 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -119,6 +119,12 @@ #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 */ @@ -2171,6 +2177,10 @@ __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. @@ -3324,6 +3334,12 @@ 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 cb57da499ebb..5e9ae0e6a727 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -135,6 +135,10 @@ static enum sysctl_writes_mode sysctl_writes_strict = SYSCTL_WRITES_STRICT; int sysctl_legacy_va_layout; #endif +#ifdef CONFIG_USER_NS +extern int unprivileged_userns_clone; +#endif + #endif /* CONFIG_SYSCTL */ /* @@ -1617,6 +1621,15 @@ static const struct ctl_table kern_table[] = { .mode = 0644, .proc_handler = proc_dointvec, }, +#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 aa0b2e47f2f2..222bb2b40b73 100644 --- a/kernel/user_namespace.c +++ b/kernel/user_namespace.c @@ -22,6 +22,9 @@ #include #include +/* sysctl */ +int unprivileged_userns_clone = 1; + static struct kmem_cache *user_ns_cachep __ro_after_init; static DEFINE_MUTEX(userns_state_mutex); -- 2.49.0