FreeBSD/Linux Kernel Cross Reference
sys/security/mac/mac_framework.c

     /*-
      * Copyright (c) 1999-2002, 2006 Robert N. M. Watson
      * Copyright (c) 2001 Ilmar S. Habibulin
      * Copyright (c) 2001-2005 Networks Associates Technology, Inc.
      * Copyright (c) 2005-2006 SPARTA, Inc.
      * All rights reserved.
      *
      * This software was developed by Robert Watson and Ilmar Habibulin for the
      * TrustedBSD Project.
     *
     * This software was developed for the FreeBSD Project in part by Network
     * Associates Laboratories, the Security Research Division of Network
     * Associates, Inc. under DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"),
     * as part of the DARPA CHATS research program.
     *
     * This software was enhanced by SPARTA ISSO under SPAWAR contract 
     * N66001-04-C-6019 ("SEFOS").
     *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     *
     * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     */
    
    /*-
     * Framework for extensible kernel access control.  This file contains core
     * kernel infrastructure for the TrustedBSD MAC Framework, including policy
     * registration, versioning, locking, error composition operator, and system
     * calls.
     *
     * The MAC Framework implements three programming interfaces:
     *
     * - The kernel MAC interface, defined in mac_framework.h, and invoked
     *   throughout the kernel to request security decisions, notify of security
     *   related events, etc.
     *
     * - The MAC policy module interface, defined in mac_policy.h, which is
     *   implemented by MAC policy modules and invoked by the MAC Framework to
     *   forward kernel security requests and notifications to policy modules.
     *
     * - The user MAC API, defined in mac.h, which allows user programs to query
     *   and set label state on objects.
     *
     * The majority of the MAC Framework implementation may be found in
     * src/sys/security/mac.  Sample policy modules may be found in
     * src/sys/security/mac_*.
     */
    
    #include "opt_mac.h"
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD$");
    
    #include <sys/param.h>
    #include <sys/condvar.h>
    #include <sys/kernel.h>
    #include <sys/lock.h>
    #include <sys/mutex.h>
    #include <sys/mac.h>
    #include <sys/module.h>
    #include <sys/systm.h>
    #include <sys/sysctl.h>
    
    #include <security/mac/mac_framework.h>
    #include <security/mac/mac_internal.h>
    #include <security/mac/mac_policy.h>
    
    /*
     * Root sysctl node for all MAC and MAC policy controls.
     */
    SYSCTL_NODE(_security, OID_AUTO, mac, CTLFLAG_RW, 0,
        "TrustedBSD MAC policy controls");
    
    /*
     * Declare that the kernel provides MAC support, version 3 (FreeBSD 7.x).
     * This permits modules to refuse to be loaded if the necessary support isn't
     * present, even if it's pre-boot.
     */
    MODULE_VERSION(kernel_mac_support, MAC_VERSION);
    
    static unsigned int     mac_version = MAC_VERSION;
    SYSCTL_UINT(_security_mac, OID_AUTO, version, CTLFLAG_RD, &mac_version, 0,
        "");
   
   /*
    * Labels consist of a indexed set of "slots", which are allocated policies
    * as required.  The MAC Framework maintains a bitmask of slots allocated so
    * far to prevent reuse.  Slots cannot be reused, as the MAC Framework
    * guarantees that newly allocated slots in labels will be NULL unless
    * otherwise initialized, and because we do not have a mechanism to garbage
    * collect slots on policy unload.  As labeled policies tend to be statically
    * loaded during boot, and not frequently unloaded and reloaded, this is not
    * generally an issue.
    */
   #if MAC_MAX_SLOTS > 32
   #error "MAC_MAX_SLOTS too large"
   #endif
   
   static unsigned int mac_max_slots = MAC_MAX_SLOTS;
   static unsigned int mac_slot_offsets_free = (1 << MAC_MAX_SLOTS) - 1;
   SYSCTL_UINT(_security_mac, OID_AUTO, max_slots, CTLFLAG_RD, &mac_max_slots,
       0, "");
   
   /*
    * Has the kernel started generating labeled objects yet?  All read/write
    * access to this variable is serialized during the boot process.  Following
    * the end of serialization, we don't update this flag; no locking.
    */
   static int      mac_late = 0;
   
   /*
    * Flag to indicate whether or not we should allocate label storage for new
    * mbufs.  Since most dynamic policies we currently work with don't rely on
    * mbuf labeling, try to avoid paying the cost of mtag allocation unless
    * specifically notified of interest.  One result of this is that if a
    * dynamically loaded policy requests mbuf labels, it must be able to deal
    * with a NULL label being returned on any mbufs that were already in flight
    * when the policy was loaded.  Since the policy already has to deal with
    * uninitialized labels, this probably won't be a problem.  Note: currently
    * no locking.  Will this be a problem?
    *
    * In the future, we may want to allow objects to request labeling on a per-
    * object type basis, rather than globally for all objects.
    */
   #ifndef MAC_ALWAYS_LABEL_MBUF
   int     mac_labelmbufs = 0;
   #endif
   
   MALLOC_DEFINE(M_MACTEMP, "mactemp", "MAC temporary label storage");
   
   /*
    * mac_static_policy_list holds a list of policy modules that are not loaded
    * while the system is "live", and cannot be unloaded.  These policies can be
    * invoked without holding the busy count.
    *
    * mac_policy_list stores the list of dynamic policies.  A busy count is
    * maintained for the list, stored in mac_policy_busy.  The busy count is
    * protected by mac_policy_mtx; the list may be modified only while the busy
    * count is 0, requiring that the lock be held to prevent new references to
    * the list from being acquired.  For almost all operations, incrementing the
    * busy count is sufficient to guarantee consistency, as the list cannot be
    * modified while the busy count is elevated.  For a few special operations
    * involving a change to the list of active policies, the mtx itself must be
    * held.  A condition variable, mac_policy_cv, is used to signal potential
    * exclusive consumers that they should try to acquire the lock if a first
    * attempt at exclusive access fails.
    *
    * This design intentionally avoids fairness, and may starve attempts to
    * acquire an exclusive lock on a busy system.  This is required because we
    * do not ever want acquiring a read reference to perform an unbounded length
    * sleep.  Read references are acquired in ithreads, network isrs, etc, and
    * any unbounded blocking could lead quickly to deadlock.
    *
    * Another reason for never blocking on read references is that the MAC
    * Framework may recurse: if a policy calls a VOP, for example, this might
    * lead to vnode life cycle operations (such as init/destroy).
    *
    * If the kernel option MAC_STATIC has been compiled in, all locking becomes
    * a no-op, and the global list of policies is not allowed to change after
    * early boot.
    *
    * XXXRW: Currently, we signal mac_policy_cv every time the framework becomes
    * unbusy and there is a thread waiting to enter it exclusively.  Since it 
    * may take some time before the thread runs, we may issue a lot of signals.
    * We should instead keep track of the fact that we've signalled, taking into 
    * account that the framework may be busy again by the time the thread runs, 
    * requiring us to re-signal. 
    */
   #ifndef MAC_STATIC
   static struct mtx mac_policy_mtx;
   static struct cv mac_policy_cv;
   static int mac_policy_count;
   static int mac_policy_wait;
   #endif
   struct mac_policy_list_head mac_policy_list;
   struct mac_policy_list_head mac_static_policy_list;
   
   /*
    * We manually invoke WITNESS_WARN() to allow Witness to generate warnings
    * even if we don't end up ever triggering the wait at run-time.  The
    * consumer of the exclusive interface must not hold any locks (other than
    * potentially Giant) since we may sleep for long (potentially indefinite)
    * periods of time waiting for the framework to become quiescent so that a
    * policy list change may be made.
    */
   void
   mac_policy_grab_exclusive(void)
   {
   
   #ifndef MAC_STATIC
           if (!mac_late)
                   return;
   
           WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL,
               "mac_policy_grab_exclusive() at %s:%d", __FILE__, __LINE__);
           mtx_lock(&mac_policy_mtx);
           while (mac_policy_count != 0) {
                   mac_policy_wait++;
                   cv_wait(&mac_policy_cv, &mac_policy_mtx);
                   mac_policy_wait--;
           }
   #endif
   }
   
   void
   mac_policy_assert_exclusive(void)
   {
   
   #ifndef MAC_STATIC
           if (!mac_late)
                   return;
   
           mtx_assert(&mac_policy_mtx, MA_OWNED);
           KASSERT(mac_policy_count == 0,
               ("mac_policy_assert_exclusive(): not exclusive"));
   #endif
   }
   
   void
   mac_policy_release_exclusive(void)
   {
   #ifndef MAC_STATIC
           int dowakeup;
   
           if (!mac_late)
                   return;
   
           KASSERT(mac_policy_count == 0,
               ("mac_policy_release_exclusive(): not exclusive"));
           dowakeup = (mac_policy_wait != 0);
           mtx_unlock(&mac_policy_mtx);
           if (dowakeup)
                   cv_signal(&mac_policy_cv);
   #endif
   }
   
   void
   mac_policy_list_busy(void)
   {
   
   #ifndef MAC_STATIC
           if (!mac_late)
                   return;
   
           mtx_lock(&mac_policy_mtx);
           mac_policy_count++;
           mtx_unlock(&mac_policy_mtx);
   #endif
   }
   
   int
   mac_policy_list_conditional_busy(void)
   {
   #ifndef MAC_STATIC
           int ret;
   
           if (!mac_late)
                   return (1);
   
           mtx_lock(&mac_policy_mtx);
           if (!LIST_EMPTY(&mac_policy_list)) {
                   mac_policy_count++;
                   ret = 1;
           } else
                   ret = 0;
           mtx_unlock(&mac_policy_mtx);
           return (ret);
   #else
           return (1);
   #endif
   }
   
   void
   mac_policy_list_unbusy(void)
   {
   #ifndef MAC_STATIC
           int dowakeup;
   
           if (!mac_late)
                   return;
   
           mtx_lock(&mac_policy_mtx);
           mac_policy_count--;
           KASSERT(mac_policy_count >= 0, ("MAC_POLICY_LIST_LOCK"));
           dowakeup = (mac_policy_count == 0 && mac_policy_wait != 0);
           mtx_unlock(&mac_policy_mtx);
   
           if (dowakeup)
                   cv_signal(&mac_policy_cv);
   #endif
   }
   
   /*
    * Initialize the MAC subsystem, including appropriate SMP locks.
    */
   static void
   mac_init(void)
   {
   
           LIST_INIT(&mac_static_policy_list);
           LIST_INIT(&mac_policy_list);
           mac_labelzone_init();
   
   #ifndef MAC_STATIC
           mtx_init(&mac_policy_mtx, "mac_policy_mtx", NULL, MTX_DEF);
           cv_init(&mac_policy_cv, "mac_policy_cv");
   #endif
   }
   
   /*
    * For the purposes of modules that want to know if they were loaded "early",
    * set the mac_late flag once we've processed modules either linked into the
    * kernel, or loaded before the kernel startup.
    */
   static void
   mac_late_init(void)
   {
   
           mac_late = 1;
   }
   
   /*
    * After the policy list has changed, walk the list to update any global
    * flags.  Currently, we support only one flag, and it's conditionally
    * defined; as a result, the entire function is conditional.  Eventually, the
    * #else case might also iterate across the policies.
    */
   static void
   mac_policy_updateflags(void)
   {
   #ifndef MAC_ALWAYS_LABEL_MBUF
           struct mac_policy_conf *tmpc;
           int labelmbufs;
   
           mac_policy_assert_exclusive();
   
           labelmbufs = 0;
           LIST_FOREACH(tmpc, &mac_static_policy_list, mpc_list) {
                   if (tmpc->mpc_loadtime_flags & MPC_LOADTIME_FLAG_LABELMBUFS)
                           labelmbufs++;
           }
           LIST_FOREACH(tmpc, &mac_policy_list, mpc_list) {
                   if (tmpc->mpc_loadtime_flags & MPC_LOADTIME_FLAG_LABELMBUFS)
                           labelmbufs++;
           }
           mac_labelmbufs = (labelmbufs != 0);
   #endif
   }
   
   static int
   mac_policy_register(struct mac_policy_conf *mpc)
   {
           struct mac_policy_conf *tmpc;
           int error, slot, static_entry;
   
           error = 0;
   
           /*
            * We don't technically need exclusive access while !mac_late, but
            * hold it for assertion consistency.
            */
           mac_policy_grab_exclusive();
   
           /*
            * If the module can potentially be unloaded, or we're loading late,
            * we have to stick it in the non-static list and pay an extra
            * performance overhead.  Otherwise, we can pay a light locking cost
            * and stick it in the static list.
            */
           static_entry = (!mac_late &&
               !(mpc->mpc_loadtime_flags & MPC_LOADTIME_FLAG_UNLOADOK));
   
           if (static_entry) {
                   LIST_FOREACH(tmpc, &mac_static_policy_list, mpc_list) {
                           if (strcmp(tmpc->mpc_name, mpc->mpc_name) == 0) {
                                   error = EEXIST;
                                   goto out;
                           }
                   }
           } else {
                   LIST_FOREACH(tmpc, &mac_policy_list, mpc_list) {
                           if (strcmp(tmpc->mpc_name, mpc->mpc_name) == 0) {
                                   error = EEXIST;
                                   goto out;
                           }
                   }
           }
           if (mpc->mpc_field_off != NULL) {
                   slot = ffs(mac_slot_offsets_free);
                   if (slot == 0) {
                           error = ENOMEM;
                           goto out;
                   }
                   slot--;
                   mac_slot_offsets_free &= ~(1 << slot);
                   *mpc->mpc_field_off = slot;
           }
           mpc->mpc_runtime_flags |= MPC_RUNTIME_FLAG_REGISTERED;
   
           /*
            * If we're loading a MAC module after the framework has initialized,
            * it has to go into the dynamic list.  If we're loading it before
            * we've finished initializing, it can go into the static list with
            * weaker locker requirements.
            */
           if (static_entry)
                   LIST_INSERT_HEAD(&mac_static_policy_list, mpc, mpc_list);
           else
                   LIST_INSERT_HEAD(&mac_policy_list, mpc, mpc_list);
   
           /*
            * Per-policy initialization.  Currently, this takes place under the
            * exclusive lock, so policies must not sleep in their init method.
            * In the future, we may want to separate "init" from "start", with
            * "init" occuring without the lock held.  Likewise, on tear-down,
            * breaking out "stop" from "destroy".
            */
           if (mpc->mpc_ops->mpo_init != NULL)
                   (*(mpc->mpc_ops->mpo_init))(mpc);
           mac_policy_updateflags();
   
           printf("Security policy loaded: %s (%s)\n", mpc->mpc_fullname,
               mpc->mpc_name);
   
   out:
           mac_policy_release_exclusive();
           return (error);
   }
   
   static int
   mac_policy_unregister(struct mac_policy_conf *mpc)
   {
   
           /*
            * If we fail the load, we may get a request to unload.  Check to see
            * if we did the run-time registration, and if not, silently succeed.
            */
           mac_policy_grab_exclusive();
           if ((mpc->mpc_runtime_flags & MPC_RUNTIME_FLAG_REGISTERED) == 0) {
                   mac_policy_release_exclusive();
                   return (0);
           }
   #if 0
           /*
            * Don't allow unloading modules with private data.
            */
           if (mpc->mpc_field_off != NULL) {
                   MAC_POLICY_LIST_UNLOCK();
                   return (EBUSY);
           }
   #endif
           /*
            * Only allow the unload to proceed if the module is unloadable by
            * its own definition.
            */
           if ((mpc->mpc_loadtime_flags & MPC_LOADTIME_FLAG_UNLOADOK) == 0) {
                   mac_policy_release_exclusive();
                   return (EBUSY);
           }
           if (mpc->mpc_ops->mpo_destroy != NULL)
                   (*(mpc->mpc_ops->mpo_destroy))(mpc);
   
           LIST_REMOVE(mpc, mpc_list);
           mpc->mpc_runtime_flags &= ~MPC_RUNTIME_FLAG_REGISTERED;
           mac_policy_updateflags();
   
           mac_policy_release_exclusive();
   
           printf("Security policy unload: %s (%s)\n", mpc->mpc_fullname,
               mpc->mpc_name);
   
           return (0);
   }
   
   /*
    * Allow MAC policy modules to register during boot, etc.
    */
   int
   mac_policy_modevent(module_t mod, int type, void *data)
   {
           struct mac_policy_conf *mpc;
           int error;
   
           error = 0;
           mpc = (struct mac_policy_conf *) data;
   
   #ifdef MAC_STATIC
           if (mac_late) {
                   printf("mac_policy_modevent: MAC_STATIC and late\n");
                   return (EBUSY);
           }
   #endif
   
           switch (type) {
           case MOD_LOAD:
                   if (mpc->mpc_loadtime_flags & MPC_LOADTIME_FLAG_NOTLATE &&
                       mac_late) {
                           printf("mac_policy_modevent: can't load %s policy "
                               "after booting\n", mpc->mpc_name);
                           error = EBUSY;
                           break;
                   }
                   error = mac_policy_register(mpc);
                   break;
           case MOD_UNLOAD:
                   /* Don't unregister the module if it was never registered. */
                   if ((mpc->mpc_runtime_flags & MPC_RUNTIME_FLAG_REGISTERED)
                       != 0)
                           error = mac_policy_unregister(mpc);
                   else
                           error = 0;
                   break;
           default:
                   error = EOPNOTSUPP;
                   break;
           }
   
           return (error);
   }
   
   /*
    * Define an error value precedence, and given two arguments, selects the
    * value with the higher precedence.
    */
   int
   mac_error_select(int error1, int error2)
   {
   
           /* Certain decision-making errors take top priority. */
           if (error1 == EDEADLK || error2 == EDEADLK)
                   return (EDEADLK);
   
           /* Invalid arguments should be reported where possible. */
           if (error1 == EINVAL || error2 == EINVAL)
                   return (EINVAL);
   
           /* Precedence goes to "visibility", with both process and file. */
           if (error1 == ESRCH || error2 == ESRCH)
                   return (ESRCH);
   
           if (error1 == ENOENT || error2 == ENOENT)
                   return (ENOENT);
   
           /* Precedence goes to DAC/MAC protections. */
           if (error1 == EACCES || error2 == EACCES)
                   return (EACCES);
   
           /* Precedence goes to privilege. */
           if (error1 == EPERM || error2 == EPERM)
                   return (EPERM);
   
           /* Precedence goes to error over success; otherwise, arbitrary. */
           if (error1 != 0)
                   return (error1);
           return (error2);
   }
   
   int
   mac_check_structmac_consistent(struct mac *mac)
   {
   
           if (mac->m_buflen < 0 ||
               mac->m_buflen > MAC_MAX_LABEL_BUF_LEN)
                   return (EINVAL);
   
           return (0);
   }
   
   SYSINIT(mac, SI_SUB_MAC, SI_ORDER_FIRST, mac_init, NULL);
   SYSINIT(mac_late, SI_SUB_MAC_LATE, SI_ORDER_FIRST, mac_late_init, NULL);

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