This is a note to let you know that I've just added the patch titled
userns: Don't allow setgroups until a gid mapping has been setablished
to the 3.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
userns-don-t-allow-setgroups-until-a-gid-mapping-has-been-setablished.patch
and it can be found in the queue-3.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 273d2c67c3e179adb1e74f403d1e9a06e3f841b5 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Date: Fri, 5 Dec 2014 18:01:11 -0600
Subject: userns: Don't allow setgroups until a gid mapping has been setablished
From: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
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@xxxxxxxxxxxxxx>
Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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;
Patches currently in stable-queue which might be from ebiederm@xxxxxxxxxxxx are
queue-3.10/mnt-update-unprivileged-remount-test.patch
queue-3.10/userns-check-euid-no-fsuid-when-establishing-an-unprivileged-uid-mapping.patch
queue-3.10/mnt-implicitly-add-mnt_nodev-on-remount-when-it-was-implicitly-added-by-mount.patch
queue-3.10/userns-don-t-allow-unprivileged-creation-of-gid-mappings.patch
queue-3.10/userns-rename-id_map_mutex-to-userns_state_mutex.patch
queue-3.10/userns-add-a-knob-to-disable-setgroups-on-a-per-user-namespace-basis.patch
queue-3.10/userns-allow-setting-gid_maps-without-privilege-when-setgroups-is-disabled.patch
queue-3.10/userns-don-t-allow-setgroups-until-a-gid-mapping-has-been-setablished.patch
queue-3.10/groups-consolidate-the-setgroups-permission-checks.patch
queue-3.10/userns-only-allow-the-creator-of-the-userns-unprivileged-mappings.patch
queue-3.10/userns-document-what-the-invariant-required-for-safe-unprivileged-mappings.patch
queue-3.10/umount-disallow-unprivileged-mount-force.patch
queue-3.10/userns-unbreak-the-unprivileged-remount-tests.patch
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