path: root/kernel
diff options
authorEric W. Biederman <ebiederm@xmission.com>2014-12-05 18:01:11 -0600
committerEric W. Biederman <ebiederm@xmission.com>2014-12-09 16:58:40 -0600
commit273d2c67c3e179adb1e74f403d1e9a06e3f841b5 (patch)
tree500bf14c930ea5c1db4c40dec54d95a00085552c /kernel
parent0542f17bf2c1f2430d368f44c8fcf2f82ec9e53e (diff)
userns: Don't allow setgroups until a gid mapping has been setablished
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. Cc: stable@vger.kernel.org Reviewed-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Diffstat (limited to 'kernel')
2 files changed, 17 insertions, 1 deletions
diff --git a/kernel/groups.c b/kernel/groups.c
index 02d8a251c476..664411f171b5 100644
--- 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 */
@@ -217,7 +218,8 @@ 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);
diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
index b99c862a2e3f..27c8dab48c07 100644
--- a/kernel/user_namespace.c
+++ b/kernel/user_namespace.c
@@ -843,6 +843,20 @@ static bool new_idmap_permitted(const struct file *file,
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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