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From: Serge Hallyn <serge.hallyn@canonical.com>
Date: Fri, 31 May 2013 19:12:12 +0000 (+0100)
Subject: 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]
---
kernel/fork.c | 16 ++++++++++++++++
kernel/sysctl.c | 13 +++++++++++++
kernel/user_namespace.c | 3 +++
3 files changed, 32 insertions(+)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -122,6 +122,12 @@
#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
*/
@@ -1933,6 +1939,10 @@ __latent_entropy struct task_struct *cop
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.
@@ -3099,6 +3109,12 @@ int ksys_unshare(unsigned long unshare_f
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;
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -77,6 +77,10 @@ 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
/**
@@ -1581,6 +1585,15 @@ int proc_do_static_key(const struct ctl_
}
static const struct ctl_table kern_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 = "tainted",
--- 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);
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