add sysctl to disallow unprivileged CLONE_NEWUSER by default

Origin: http://kernel.ubuntu.com/git?p=serge%2Fubuntu-saucy.git;a=commit;h=5c847404dcb2e3195ad0057877e1422ae90892b8

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 <serge.hallyn@ubuntu.com>
[bwh: Remove unneeded binary sysctl bits]
[bwh: Keep this sysctl, but change the default to enabled]

Gbp-Pq: Topic debian
Gbp-Pq: Name add-sysctl-to-disallow-unprivileged-CLONE_NEWUSER-by-default.patch

diff --git a/kernel/fork.c b/kernel/fork.c
index b1f3915d5f8ec887b96a59b799797c34be91c231..83cb05d01836b1d42a37e22f350db7ed70448474 100644 (file)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -123,6 +123,12 @@
 
 #include <kunit/visibility.h>
 
+#ifdef CONFIG_USER_NS
+extern int unprivileged_userns_clone;
+#else
+#define unprivileged_userns_clone 0
+#endif
+
 /*
  * Minimum number of threads to boot the kernel
  */
@@ -1986,6 +1992,10 @@ __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.
@@ -3149,6 +3159,12 @@ 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 2cd767b9680eb696efeae06f436548777b1b6844..94cd4f0c182f60b387065709b570a85e4f739323 100644 (file)
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -35,6 +35,10 @@ EXPORT_SYMBOL_GPL(sysctl_long_vals);
 static const int ngroups_max = NGROUPS_MAX;
 static const int cap_last_cap = CAP_LAST_CAP;
 
+#ifdef CONFIG_USER_NS
+extern int unprivileged_userns_clone;
+#endif
+
 #ifdef CONFIG_PROC_SYSCTL
 
 /**
@@ -1122,6 +1126,15 @@ int proc_do_static_key(const struct ctl_table *table, int dir,
 }
 
 static const struct ctl_table sysctl_subsys_table[] = {
+#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       = "sysctl_writes_strict",

diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index 03cb63883d041a3c82dc89357af307bd41dcbfff..163817801c17520d3758a8f020489b8d00f1a718 100644 (file)
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -23,6 +23,9 @@
 #include <linux/sort.h>
 #include <linux/nstree.h>
 
+/* sysctl */
+int unprivileged_userns_clone = 1;
+
 static struct kmem_cache *user_ns_cachep __ro_after_init;
 static DEFINE_MUTEX(userns_state_mutex);