userns: security: make capabilities relative to the user namespace
- Introduce ns_capable to test for a capability in a non-default
user namespace.
- Teach cap_capable to handle capabilities in a non-default
user namespace.
The motivation is to get to the unprivileged creation of new
namespaces. It looks like this gets us 90% of the way there, with
only potential uid confusion issues left.
I still need to handle getting all caps after creation but otherwise I
think I have a good starter patch that achieves all of your goals.
Changelog:
11/05/2010: [serge] add apparmor
12/14/2010: [serge] fix capabilities to created user namespaces
Without this, if user serge creates a user_ns, he won't have
capabilities to the user_ns he created. THis is because we
were first checking whether his effective caps had the caps
he needed and returning -EPERM if not, and THEN checking whether
he was the creator. Reverse those checks.
12/16/2010: [serge] security_real_capable needs ns argument in !security case
01/11/2011: [serge] add task_ns_capable helper
01/11/2011: [serge] add nsown_capable() helper per Bastian Blank suggestion
02/16/2011: [serge] fix a logic bug: the root user is always creator of
init_user_ns, but should not always have capabilities to
it! Fix the check in cap_capable().
02/21/2011: Add the required user_ns parameter to security_capable,
fixing a compile failure.
02/23/2011: Convert some macros to functions as per akpm comments. Some
couldn't be converted because we can't easily forward-declare
them (they are inline if !SECURITY, extern if SECURITY). Add
a current_user_ns function so we can use it in capability.h
without #including cred.h. Move all forward declarations
together to the top of the #ifdef __KERNEL__ section, and use
kernel-doc format.
02/23/2011: Per dhowells, clean up comment in cap_capable().
02/23/2011: Per akpm, remove unreachable 'return -EPERM' in cap_capable.
(Original written and signed off by Eric; latest, modified version
acked by him)
[akpm@linux-foundation.org: fix build]
[akpm@linux-foundation.org: export current_user_ns() for ecryptfs]
[serge.hallyn@canonical.com: remove unneeded extra argument in selinux's task_has_capability]
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Serge E. Hallyn <serge.hallyn@canonical.com>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Acked-by: Daniel Lezcano <daniel.lezcano@free.fr>
Acked-by: David Howells <dhowells@redhat.com>
Cc: James Morris <jmorris@namei.org>
Signed-off-by: Serge E. Hallyn <serge.hallyn@canonical.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/kernel/capability.c b/kernel/capability.c
index 9e9385f..0a3d2c8 100644
--- a/kernel/capability.c
+++ b/kernel/capability.c
@@ -14,6 +14,7 @@
#include <linux/security.h>
#include <linux/syscalls.h>
#include <linux/pid_namespace.h>
+#include <linux/user_namespace.h>
#include <asm/uaccess.h>
/*
@@ -299,17 +300,48 @@
* This sets PF_SUPERPRIV on the task if the capability is available on the
* assumption that it's about to be used.
*/
-int capable(int cap)
+bool capable(int cap)
+{
+ return ns_capable(&init_user_ns, cap);
+}
+EXPORT_SYMBOL(capable);
+
+/**
+ * ns_capable - Determine if the current task has a superior capability in effect
+ * @ns: The usernamespace we want the capability in
+ * @cap: The capability to be tested for
+ *
+ * Return true if the current task has the given superior capability currently
+ * available for use, false if not.
+ *
+ * This sets PF_SUPERPRIV on the task if the capability is available on the
+ * assumption that it's about to be used.
+ */
+bool ns_capable(struct user_namespace *ns, int cap)
{
if (unlikely(!cap_valid(cap))) {
printk(KERN_CRIT "capable() called with invalid cap=%u\n", cap);
BUG();
}
- if (security_capable(current_cred(), cap) == 0) {
+ if (security_capable(ns, current_cred(), cap) == 0) {
current->flags |= PF_SUPERPRIV;
- return 1;
+ return true;
}
- return 0;
+ return false;
}
-EXPORT_SYMBOL(capable);
+EXPORT_SYMBOL(ns_capable);
+
+/**
+ * task_ns_capable - Determine whether current task has a superior
+ * capability targeted at a specific task's user namespace.
+ * @t: The task whose user namespace is targeted.
+ * @cap: The capability in question.
+ *
+ * Return true if it does, false otherwise.
+ */
+bool task_ns_capable(struct task_struct *t, int cap)
+{
+ return ns_capable(task_cred_xxx(t, user)->user_ns, cap);
+}
+EXPORT_SYMBOL(task_ns_capable);