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 97c9afe3efc38da1acc466a7e385ddbae0176395..fc298dbb5675c133d4f833d8497c110e26a9880b 100644 (file)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -120,6 +120,12 @@
 
 #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
  */
@@ -2162,6 +2168,10 @@ __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.
@@ -3315,6 +3325,12 @@ 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 79e6cb1d5c48f8e4f48580114f09bed9d65481af..382c9c451bd597d38b9bb1bfb919508b8c2a1d58 100644 (file)
--- 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 */
 
 /*
@@ -1618,6 +1622,15 @@ static 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 aa0b2e47f2f21bef96c45e09aaa4bc05dc5216b9..222bb2b40b73b6188a9c06be5aa52fc4e439326a 100644 (file)
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -22,6 +22,9 @@
 #include <linux/bsearch.h>
 #include <linux/sort.h>
 
+/* sysctl */
+int unprivileged_userns_clone = 1;
+
 static struct kmem_cache *user_ns_cachep __ro_after_init;
 static DEFINE_MUTEX(userns_state_mutex);