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 70d09daf4ab92435d4a0462322c6f5699122dd57..f48978864cd05269b89e5ab2d5ef2476271fbc71 100644 (file)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -107,6 +107,11 @@
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/task.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
@@ -1872,6 +1877,10 @@ 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.
@@ -2937,6 +2946,12 @@ 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 b9306d2bb4269e8fb5a12664a0e17359f8df2076..afb0b0344d9a9d3c60bad0fcc1fe5c3c2a670240 100644 (file)
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -200,6 +200,10 @@ static int min_extfrag_threshold;
 static int max_extfrag_threshold = 1000;
 #endif
 
+#ifdef CONFIG_USER_NS
+extern int unprivileged_userns_clone;
+#endif
+
 #endif /* CONFIG_SYSCTL */
 
 #if defined(CONFIG_BPF_SYSCALL) && defined(CONFIG_SYSCTL)
@@ -1902,6 +1906,15 @@ 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 e703d5d9cbe8e66121af6b14d4855ed44472576d..9f6b8b0bac62722f79594d0b178980696a5699a9 100644 (file)
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -21,6 +21,9 @@
 #include <linux/bsearch.h>
 #include <linux/sort.h>
 
+/* sysctl */
+int unprivileged_userns_clone = 1;
+
 static struct kmem_cache *user_ns_cachep __read_mostly;
 static DEFINE_MUTEX(userns_state_mutex);