Eric Lee / smarc-ti-linux-kernel

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Commit d5c3ebc43923644c61155b6b71f9b1a36d570343

Authored by Eric W. Biederman
Committed by Greg Kroah-Hartman
1 parent d9a75912fc

userns: Don't allow setgroups until a gid mapping has been setablished 

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>

Showing 3 changed files with 22 additions and 1 deletions Side-by-side Diff

include/linux/user_namespace.h
Diff comments   View file @ d5c3ebc
... ... @@ -63,6 +63,7 @@
63 63 extern ssize_t proc_uid_map_write(struct file *, const char __user *, size_t, loff_t *);
64 64 extern ssize_t proc_gid_map_write(struct file *, const char __user *, size_t, loff_t *);
65 65 extern ssize_t proc_projid_map_write(struct file *, const char __user *, size_t, loff_t *);
  66 +extern bool userns_may_setgroups(const struct user_namespace *ns);
66 67 #else
67 68  
68 69 static inline struct user_namespace *get_user_ns(struct user_namespace *ns)
... ... @@ -87,6 +88,10 @@
87 88 {
88 89 }
89 90  
  91 +static inline bool userns_may_setgroups(const struct user_namespace *ns)
  92 +{
  93 + return true;
  94 +}
90 95 #endif
91 96  
92 97 #endif /* _LINUX_USER_H */
... ... @@ -6,6 +6,7 @@
6 6 #include <linux/slab.h>
7 7 #include <linux/security.h>
8 8 #include <linux/syscalls.h>
  9 +#include <linux/user_namespace.h>
9 10 #include <asm/uaccess.h>
10 11  
11 12 /* init to 2 - one for init_task, one to ensure it is never freed */
... ... @@ -217,7 +218,8 @@
217 218 {
218 219 struct user_namespace *user_ns = current_user_ns();
219 220  
220   - return ns_capable(user_ns, CAP_SETGID);
  221 + return ns_capable(user_ns, CAP_SETGID) &&
  222 + userns_may_setgroups(user_ns);
221 223 }
222 224  
223 225 /*
kernel/user_namespace.c
Diff comments   View file @ d5c3ebc
... ... @@ -843,6 +843,20 @@
843 843 return false;
844 844 }
845 845  
  846 +bool userns_may_setgroups(const struct user_namespace *ns)
  847 +{
  848 + bool allowed;
  849 +
  850 + mutex_lock(&id_map_mutex);
  851 + /* It is not safe to use setgroups until a gid mapping in
  852 + * the user namespace has been established.
  853 + */
  854 + allowed = ns->gid_map.nr_extents != 0;
  855 + mutex_unlock(&id_map_mutex);
  856 +
  857 + return allowed;
  858 +}
  859 +
846 860 static void *userns_get(struct task_struct *task)
847 861 {
848 862 struct user_namespace *user_ns;