From 6e99903c40381bf6c88d4a1b09e4afd75d6acd58 Mon Sep 17 00:00:00 2001 From: Serge Hallyn Date: Fri, 31 May 2013 19:12:12 +0100 Subject: [PATCH] sysctl: 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] Signed-off-by: Alexandre Frade --- kernel/fork.c | 15 +++++++++++++++ kernel/sysctl.c | 13 +++++++++++++ kernel/user_namespace.c | 3 +++ 3 files changed, 31 insertions(+) diff --git a/kernel/fork.c b/kernel/fork.c index 08969f5aa38d..579257328895 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -108,6 +108,11 @@ #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 @@ -2008,6 +2013,10 @@ 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. @@ -3166,6 +3175,12 @@ 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 59affecacaf8..4e37935ab320 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -137,6 +137,10 @@ 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 */ /* @@ -1669,6 +1673,15 @@ static struct ctl_table kern_table[] = { .extra1 = SYSCTL_ZERO, .extra2 = SYSCTL_TWO, }, +#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 54211dbd516c..43c4c079c554 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 __read_mostly; static DEFINE_MUTEX(userns_state_mutex); -- 2.35.1