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Subject[PATCH 3.10 23/38] userns: Dont allow setgroups until a gid mapping has been setablished
Date
3.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: "Eric W. Biederman" <ebiederm@xmission.com>

commit 273d2c67c3e179adb1e74f403d1e9a06e3f841b5 upstream.

setgroups is unique in not needing a valid mapping before it can be called,
in the case of setgroups(0, NULL) which drops all supplemental groups.

The design of the user namespace assumes that CAP_SETGID can not actually
be used until a gid mapping is established. Therefore add a helper function
to see if the user namespace gid mapping has been established and call
that function in the setgroups permission check.

This is part of the fix for CVE-2014-8989, being able to drop groups
without privilege using user namespaces.

Reviewed-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
include/linux/user_namespace.h | 5 +++++
kernel/groups.c | 4 +++-
kernel/user_namespace.c | 14 ++++++++++++++
3 files changed, 22 insertions(+), 1 deletion(-)

--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -59,6 +59,7 @@ extern struct seq_operations proc_projid
extern ssize_t proc_uid_map_write(struct file *, const char __user *, size_t, loff_t *);
extern ssize_t proc_gid_map_write(struct file *, const char __user *, size_t, loff_t *);
extern ssize_t proc_projid_map_write(struct file *, const char __user *, size_t, loff_t *);
+extern bool userns_may_setgroups(const struct user_namespace *ns);
#else

static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
@@ -83,6 +84,10 @@ static inline void put_user_ns(struct us
{
}

+static inline bool userns_may_setgroups(const struct user_namespace *ns)
+{
+ return true;
+}
#endif

void update_mnt_policy(struct user_namespace *userns);
--- a/kernel/groups.c
+++ b/kernel/groups.c
@@ -6,6 +6,7 @@
#include <linux/slab.h>
#include <linux/security.h>
#include <linux/syscalls.h>
+#include <linux/user_namespace.h>
#include <asm/uaccess.h>

/* init to 2 - one for init_task, one to ensure it is never freed */
@@ -227,7 +228,8 @@ bool may_setgroups(void)
{
struct user_namespace *user_ns = current_user_ns();

- return ns_capable(user_ns, CAP_SETGID);
+ return ns_capable(user_ns, CAP_SETGID) &&
+ userns_may_setgroups(user_ns);
}

/*
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -832,6 +832,20 @@ static bool new_idmap_permitted(const st
return false;
}

+bool userns_may_setgroups(const struct user_namespace *ns)
+{
+ bool allowed;
+
+ mutex_lock(&id_map_mutex);
+ /* It is not safe to use setgroups until a gid mapping in
+ * the user namespace has been established.
+ */
+ allowed = ns->gid_map.nr_extents != 0;
+ mutex_unlock(&id_map_mutex);
+
+ return allowed;
+}
+
static void *userns_get(struct task_struct *task)
{
struct user_namespace *user_ns;



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