From: Serge Hallyn <serge.hallyn@canonical.com>
Date: Fri, 31 May 2013 18:12:12 +0000 (+0100)
Subject: add sysctl to disallow unprivileged CLONE_NEWUSER by default
X-Git-Tag: archive/raspbian/5.2.17-1+rpi1^2~92
X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=563653039d4f6ec40c777c42277c56b649044c09;p=linux.git

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 <serge.hallyn@ubuntu.com>
[bwh: Remove unneeded binary sysctl bits]

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 fbaaece1b5b..96a2d53cb0e 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -106,6 +106,11 @@
 
 #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
@@ -1766,6 +1771,10 @@ 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.
@@ -2654,6 +2663,12 @@ 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 1beca96fb62..fb9633b8b38 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -110,6 +110,9 @@ extern int core_uses_pid;
 extern char core_pattern[];
 extern unsigned int core_pipe_limit;
 #endif
+#ifdef CONFIG_USER_NS
+extern int unprivileged_userns_clone;
+#endif
 extern int pid_max;
 extern int pid_max_min, pid_max_max;
 extern int percpu_pagelist_fraction;
@@ -532,6 +535,15 @@ 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 0eff45ce770..b2f8b577767 100644
--- 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;
+
 static struct kmem_cache *user_ns_cachep __read_mostly;
 static DEFINE_MUTEX(userns_state_mutex);