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

     /*-
      * Copyright (c) 1999-2002, 2006, 2009 Robert N. M. Watson
      * Copyright (c) 2001 Ilmar S. Habibulin
      * Copyright (c) 2001-2005 Networks Associates Technology, Inc.
      * Copyright (c) 2005-2006 SPARTA, Inc.
      * Copyright (c) 2008-2009 Apple 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").
     *
     * This software was developed at the University of Cambridge Computer
     * Laboratory with support from a grant from Google, Inc.
     *
     * 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: releng/11.0/sys/security/mac/mac_framework.c 299187 2016-05-06 16:59:04Z pfg $");
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/condvar.h>
    #include <sys/kernel.h>
    #include <sys/lock.h>
    #include <sys/mac.h>
    #include <sys/module.h>
    #include <sys/rmlock.h>
    #include <sys/sdt.h>
    #include <sys/sx.h>
    #include <sys/sysctl.h>
    
    #include <security/mac/mac_framework.h>
    #include <security/mac/mac_internal.h>
    #include <security/mac/mac_policy.h>
    
    /*
     * DTrace SDT providers for MAC.
     */
    SDT_PROVIDER_DEFINE(mac);
    SDT_PROVIDER_DEFINE(mac_framework);
    
    SDT_PROBE_DEFINE2(mac, , policy, modevent, "int",
        "struct mac_policy_conf *");
    SDT_PROBE_DEFINE1(mac, , policy, register,
        "struct mac_policy_conf *");
   SDT_PROBE_DEFINE1(mac, , policy, unregister,
       "struct mac_policy_conf *");
   
   /*
    * 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;
   
   /*
    * Each policy declares a mask of object types requiring labels to be
    * allocated for them.  For convenience, we combine and cache the bitwise or
    * of the per-policy object flags to track whether we will allocate a label
    * for an object type at run-time.
    */
   uint64_t        mac_labeled;
   SYSCTL_UQUAD(_security_mac, OID_AUTO, labeled, CTLFLAG_RD, &mac_labeled, 0,
       "Mask of object types being labeled");
   
   MALLOC_DEFINE(M_MACTEMP, "mactemp", "MAC temporary label storage");
   
   /*
    * MAC policy modules are placed in one of two lists: mac_static_policy_list,
    * for policies that are loaded early and cannot be unloaded, and
    * mac_policy_list, which holds policies either loaded later in the boot
    * cycle or that may be unloaded.  The static policy list does not require
    * locks to iterate over, but the dynamic list requires synchronization.
    * Support for dynamic policy loading can be compiled out using the
    * MAC_STATIC kernel option.
    *
    * The dynamic policy list is protected by two locks: modifying the list
    * requires both locks to be held exclusively.  One of the locks,
    * mac_policy_rm, is acquired over policy entry points that will never sleep;
    * the other, mac_policy_sx, is acquire over policy entry points that may
    * sleep.  The former category will be used when kernel locks may be held
    * over calls to the MAC Framework, during network processing in ithreads,
    * etc.  The latter will tend to involve potentially blocking memory
    * allocations, extended attribute I/O, etc.
    */
   #ifndef MAC_STATIC
   static struct rmlock mac_policy_rm;     /* Non-sleeping entry points. */
   static struct sx mac_policy_sx;         /* Sleeping entry points. */
   #endif
   
   struct mac_policy_list_head mac_policy_list;
   struct mac_policy_list_head mac_static_policy_list;
   u_int mac_policy_count;                 /* Registered policy count. */
   
   static void     mac_policy_xlock(void);
   static void     mac_policy_xlock_assert(void);
   static void     mac_policy_xunlock(void);
   
   void
   mac_policy_slock_nosleep(struct rm_priotracker *tracker)
   {
   
   #ifndef MAC_STATIC
           if (!mac_late)
                   return;
   
           rm_rlock(&mac_policy_rm, tracker);
   #endif
   }
   
   void
   mac_policy_slock_sleep(void)
   {
   
           WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL,
               "mac_policy_slock_sleep");
   
   #ifndef MAC_STATIC
           if (!mac_late)
                   return;
   
           sx_slock(&mac_policy_sx);
   #endif
   }
   
   void
   mac_policy_sunlock_nosleep(struct rm_priotracker *tracker)
   {
   
   #ifndef MAC_STATIC
           if (!mac_late)
                   return;
   
           rm_runlock(&mac_policy_rm, tracker);
   #endif
   }
   
   void
   mac_policy_sunlock_sleep(void)
   {
   
   #ifndef MAC_STATIC
           if (!mac_late)
                   return;
   
           sx_sunlock(&mac_policy_sx);
   #endif
   }
   
   static void
   mac_policy_xlock(void)
   {
   
           WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL,
               "mac_policy_xlock()");
   
   #ifndef MAC_STATIC
           if (!mac_late)
                   return;
   
           sx_xlock(&mac_policy_sx);
           rm_wlock(&mac_policy_rm);
   #endif
   }
   
   static void
   mac_policy_xunlock(void)
   {
   
   #ifndef MAC_STATIC
           if (!mac_late)
                   return;
   
           rm_wunlock(&mac_policy_rm);
           sx_xunlock(&mac_policy_sx);
   #endif
   }
   
   static void
   mac_policy_xlock_assert(void)
   {
   
   #ifndef MAC_STATIC
           if (!mac_late)
                   return;
   
           /* XXXRW: rm_assert(&mac_policy_rm, RA_WLOCKED); */
           sx_assert(&mac_policy_sx, SA_XLOCKED);
   #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
           rm_init_flags(&mac_policy_rm, "mac_policy_rm", RM_NOWITNESS |
               RM_RECURSE);
           sx_init_flags(&mac_policy_sx, "mac_policy_sx", SX_NOWITNESS);
   #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;
   }
   
   /*
    * Given a policy, derive from its set of non-NULL label init methods what
    * object types the policy is interested in.
    */
   static uint64_t
   mac_policy_getlabeled(struct mac_policy_conf *mpc)
   {
           uint64_t labeled;
   
   #define MPC_FLAG(method, flag)                                  \
           if (mpc->mpc_ops->mpo_ ## method != NULL)                       \
                   labeled |= (flag);                                      \
   
           labeled = 0;
           MPC_FLAG(cred_init_label, MPC_OBJECT_CRED);
           MPC_FLAG(proc_init_label, MPC_OBJECT_PROC);
           MPC_FLAG(vnode_init_label, MPC_OBJECT_VNODE);
           MPC_FLAG(inpcb_init_label, MPC_OBJECT_INPCB);
           MPC_FLAG(socket_init_label, MPC_OBJECT_SOCKET);
           MPC_FLAG(devfs_init_label, MPC_OBJECT_DEVFS);
           MPC_FLAG(mbuf_init_label, MPC_OBJECT_MBUF);
           MPC_FLAG(ipq_init_label, MPC_OBJECT_IPQ);
           MPC_FLAG(ifnet_init_label, MPC_OBJECT_IFNET);
           MPC_FLAG(bpfdesc_init_label, MPC_OBJECT_BPFDESC);
           MPC_FLAG(pipe_init_label, MPC_OBJECT_PIPE);
           MPC_FLAG(mount_init_label, MPC_OBJECT_MOUNT);
           MPC_FLAG(posixsem_init_label, MPC_OBJECT_POSIXSEM);
           MPC_FLAG(posixshm_init_label, MPC_OBJECT_POSIXSHM);
           MPC_FLAG(sysvmsg_init_label, MPC_OBJECT_SYSVMSG);
           MPC_FLAG(sysvmsq_init_label, MPC_OBJECT_SYSVMSQ);
           MPC_FLAG(sysvsem_init_label, MPC_OBJECT_SYSVSEM);
           MPC_FLAG(sysvshm_init_label, MPC_OBJECT_SYSVSHM);
           MPC_FLAG(syncache_init_label, MPC_OBJECT_SYNCACHE);
           MPC_FLAG(ip6q_init_label, MPC_OBJECT_IP6Q);
   
   #undef MPC_FLAG
           return (labeled);
   }
   
   /*
    * When policies are loaded or unloaded, walk the list of registered policies
    * and built mac_labeled, a bitmask representing the union of all objects
    * requiring labels across all policies.
    */
   static void
   mac_policy_update(void)
   {
           struct mac_policy_conf *mpc;
   
           mac_policy_xlock_assert();
   
           mac_labeled = 0;
           mac_policy_count = 0;
           LIST_FOREACH(mpc, &mac_static_policy_list, mpc_list) {
                   mac_labeled |= mac_policy_getlabeled(mpc);
                   mac_policy_count++;
           }
           LIST_FOREACH(mpc, &mac_policy_list, mpc_list) {
                   mac_labeled |= mac_policy_getlabeled(mpc);
                   mac_policy_count++;
           }
   }
   
   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_xlock();
   
           /*
            * 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" occurring 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_update();
   
           SDT_PROBE1(mac, , policy, register, mpc);
           printf("Security policy loaded: %s (%s)\n", mpc->mpc_fullname,
               mpc->mpc_name);
   
   out:
           mac_policy_xunlock();
           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_xlock();
           if ((mpc->mpc_runtime_flags & MPC_RUNTIME_FLAG_REGISTERED) == 0) {
                   mac_policy_xunlock();
                   return (0);
           }
   #if 0
           /*
            * Don't allow unloading modules with private data.
            */
           if (mpc->mpc_field_off != NULL) {
                   mac_policy_xunlock();
                   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_xunlock();
                   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_update();
           mac_policy_xunlock();
   
           SDT_PROBE1(mac, , policy, unregister, mpc);
           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
   
           SDT_PROBE2(mac, , policy, modevent, type, mpc);
           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 > 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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