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>

4 files changed, 52 insertions, 20 deletions

diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
index d21a427a35ae..ae3a698415e6 100644
--- a/security/apparmor/lsm.c
+++ b/security/apparmor/lsm.c
@@ -22,6 +22,7 @@
 #include <linux/ctype.h>
 #include <linux/sysctl.h>
 #include <linux/audit.h>
+#include <linux/user_namespace.h>
 #include <net/sock.h>
 
 #include "include/apparmor.h"
@@ -136,11 +137,11 @@ static int apparmor_capget(struct task_struct *target, kernel_cap_t *effective,
 }
 
 static int apparmor_capable(struct task_struct *task, const struct cred *cred,
-                            int cap, int audit)
+                            struct user_namespace *ns, int cap, int audit)
 {
         struct aa_profile *profile;
         /* cap_capable returns 0 on success, else -EPERM */
-        int error = cap_capable(task, cred, cap, audit);
+        int error = cap_capable(task, cred, ns, cap, audit);
         if (!error) {
                 profile = aa_cred_profile(cred);
                 if (!unconfined(profile))
diff --git a/security/commoncap.c b/security/commoncap.c
index 49c57fd60aea..43a205bc7d7c 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -27,6 +27,7 @@
 #include <linux/sched.h>
 #include <linux/prctl.h>
 #include <linux/securebits.h>
+#include <linux/user_namespace.h>
 
 /*
  * If a non-root user executes a setuid-root binary in
@@ -67,6 +68,7 @@ EXPORT_SYMBOL(cap_netlink_recv);
  * cap_capable - Determine whether a task has a particular effective capability
  * @tsk: The task to query
  * @cred: The credentials to use
+ * @ns:  The user namespace in which we need the capability
  * @cap: The capability to check for
  * @audit: Whether to write an audit message or not
  *
@@ -78,10 +80,30 @@ EXPORT_SYMBOL(cap_netlink_recv);
  * cap_has_capability() returns 0 when a task has a capability, but the
  * kernel's capable() and has_capability() returns 1 for this case.
  */
-int cap_capable(struct task_struct *tsk, const struct cred *cred, int cap,
-                int audit)
+int cap_capable(struct task_struct *tsk, const struct cred *cred,
+                struct user_namespace *targ_ns, int cap, int audit)
 {
-        return cap_raised(cred->cap_effective, cap) ? 0 : -EPERM;
+        for (;;) {
+                /* The creator of the user namespace has all caps. */
+                if (targ_ns != &init_user_ns && targ_ns->creator == cred->user)
+                        return 0;
+
+                /* Do we have the necessary capabilities? */
+                if (targ_ns == cred->user->user_ns)
+                        return cap_raised(cred->cap_effective, cap) ? 0 : -EPERM;
+
+                /* Have we tried all of the parent namespaces? */
+                if (targ_ns == &init_user_ns)
+                        return -EPERM;
+
+                /*
+                 *If you have a capability in a parent user ns, then you have
+                 * it over all children user namespaces as well.
+                 */
+                targ_ns = targ_ns->creator->user_ns;
+        }
+
+        /* We never get here */
 }
 
 /**
@@ -176,7 +198,8 @@ static inline int cap_inh_is_capped(void)
         /* they are so limited unless the current task has the CAP_SETPCAP
          * capability
          */
-        if (cap_capable(current, current_cred(), CAP_SETPCAP,
+        if (cap_capable(current, current_cred(),
+                        current_cred()->user->user_ns, CAP_SETPCAP,
                         SECURITY_CAP_AUDIT) == 0)
                 return 0;
         return 1;
@@ -828,7 +851,8 @@ int cap_task_prctl(int option, unsigned long arg2, unsigned long arg3,
                      & (new->securebits ^ arg2))                        /*[1]*/
                     || ((new->securebits & SECURE_ALL_LOCKS & ~arg2))   /*[2]*/
                     || (arg2 & ~(SECURE_ALL_LOCKS | SECURE_ALL_BITS))   /*[3]*/
-                    || (cap_capable(current, current_cred(), CAP_SETPCAP,
+                    || (cap_capable(current, current_cred(),
+                                    current_cred()->user->user_ns, CAP_SETPCAP,
                                     SECURITY_CAP_AUDIT) != 0)           /*[4]*/
                         /*
                          * [1] no changing of bits that are locked
@@ -893,7 +917,7 @@ int cap_vm_enough_memory(struct mm_struct *mm, long pages)
 {
         int cap_sys_admin = 0;
 
-        if (cap_capable(current, current_cred(), CAP_SYS_ADMIN,
+        if (cap_capable(current, current_cred(), &init_user_ns, CAP_SYS_ADMIN,
                         SECURITY_CAP_NOAUDIT) == 0)
                 cap_sys_admin = 1;
         return __vm_enough_memory(mm, pages, cap_sys_admin);
@@ -920,7 +944,7 @@ int cap_file_mmap(struct file *file, unsigned long reqprot,
         int ret = 0;
 
         if (addr < dac_mmap_min_addr) {
-                ret = cap_capable(current, current_cred(), CAP_SYS_RAWIO,
+                ret = cap_capable(current, current_cred(), &init_user_ns, CAP_SYS_RAWIO,
                                   SECURITY_CAP_AUDIT);
                 /* set PF_SUPERPRIV if it turns out we allow the low mmap */
                 if (ret == 0)
diff --git a/security/security.c b/security/security.c
index 9187665a3fdd..101142369db4 100644
--- a/security/security.c
+++ b/security/security.c
@@ -154,29 +154,33 @@ int security_capset(struct cred *new, const struct cred *old,
                                     effective, inheritable, permitted);
 }
 
-int security_capable(const struct cred *cred, int cap)
+int security_capable(struct user_namespace *ns, const struct cred *cred,
+                     int cap)
 {
-        return security_ops->capable(current, cred, cap, SECURITY_CAP_AUDIT);
+        return security_ops->capable(current, cred, ns, cap,
+                                     SECURITY_CAP_AUDIT);
 }
 
-int security_real_capable(struct task_struct *tsk, int cap)
+int security_real_capable(struct task_struct *tsk, struct user_namespace *ns,
+                          int cap)
 {
         const struct cred *cred;
         int ret;
 
         cred = get_task_cred(tsk);
-        ret = security_ops->capable(tsk, cred, cap, SECURITY_CAP_AUDIT);
+        ret = security_ops->capable(tsk, cred, ns, cap, SECURITY_CAP_AUDIT);
         put_cred(cred);
         return ret;
 }
 
-int security_real_capable_noaudit(struct task_struct *tsk, int cap)
+int security_real_capable_noaudit(struct task_struct *tsk,
+                                  struct user_namespace *ns, int cap)
 {
         const struct cred *cred;
         int ret;
 
         cred = get_task_cred(tsk);
-        ret = security_ops->capable(tsk, cred, cap, SECURITY_CAP_NOAUDIT);
+        ret = security_ops->capable(tsk, cred, ns, cap, SECURITY_CAP_NOAUDIT);
         put_cred(cred);
         return ret;
 }
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 6475e1f0223e..c67f863d3546 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -79,6 +79,7 @@
 #include <linux/mutex.h>
 #include <linux/posix-timers.h>
 #include <linux/syslog.h>
+#include <linux/user_namespace.h>
 
 #include "avc.h"
 #include "objsec.h"
@@ -1846,11 +1847,11 @@ static int selinux_capset(struct cred *new, const struct cred *old,
  */
 
 static int selinux_capable(struct task_struct *tsk, const struct cred *cred,
-                           int cap, int audit)
+                           struct user_namespace *ns, int cap, int audit)
 {
         int rc;
 
-        rc = cap_capable(tsk, cred, cap, audit);
+        rc = cap_capable(tsk, cred, ns, cap, audit);
         if (rc)
                 return rc;
 
@@ -1931,7 +1932,8 @@ static int selinux_vm_enough_memory(struct mm_struct *mm, long pages)
 {
         int rc, cap_sys_admin = 0;
 
-        rc = selinux_capable(current, current_cred(), CAP_SYS_ADMIN,
+        rc = selinux_capable(current, current_cred(),
+                             &init_user_ns, CAP_SYS_ADMIN,
                              SECURITY_CAP_NOAUDIT);
         if (rc == 0)
                 cap_sys_admin = 1;
@@ -2834,7 +2836,8 @@ static int selinux_inode_getsecurity(const struct inode *inode, const char *name
          * and lack of permission just means that we fall back to the
          * in-core context value, not a denial.
          */
-        error = selinux_capable(current, current_cred(), CAP_MAC_ADMIN,
+        error = selinux_capable(current, current_cred(),
+                                &init_user_ns, CAP_MAC_ADMIN,
                                 SECURITY_CAP_NOAUDIT);
         if (!error)
                 error = security_sid_to_context_force(isec->sid, &context,
@@ -2968,7 +2971,7 @@ static int selinux_file_ioctl(struct file *file, unsigned int cmd,
         case KDSKBENT:
         case KDSKBSENT:
                 error = task_has_capability(current, cred, CAP_SYS_TTY_CONFIG,
-                                            SECURITY_CAP_AUDIT);
+                                        SECURITY_CAP_AUDIT);
                 break;
 
         /* default case assumes that the command will go