sys/kern/kern_priv.c

   1 /*-
   2  * Copyright (c) 2006 nCircle Network Security, Inc.
   3  * All rights reserved.
   4  *
   5  * This software was developed by Robert N. M. Watson for the TrustedBSD
   6  * Project under contract to nCircle Network Security, Inc.
   7  *
   8  * Redistribution and use in source and binary forms, with or without
   9  * modification, are permitted provided that the following conditions
  10  * are met:
  11  * 1. Redistributions of source code must retain the above copyright
  12  *    notice, this list of conditions and the following disclaimer.
  13  * 2. Redistributions in binary form must reproduce the above copyright
  14  *    notice, this list of conditions and the following disclaimer in the
  15  *    documentation and/or other materials provided with the distribution.
  16  *
  17  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR, NCIRCLE NETWORK SECURITY,
  21  * INC., OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  22  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
  23  * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  24  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
  25  * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
  26  * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
  27  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  28  */
  29
  30 #include "opt_mac.h"
  31
  32 #include <sys/cdefs.h>
  33 __FBSDID("$FreeBSD$");
  34
  35 #include <sys/param.h>
  36 #include <sys/jail.h>
  37 #include <sys/kernel.h>
  38 #include <sys/priv.h>
  39 #include <sys/proc.h>
  40 #include <sys/sysctl.h>
  41 #include <sys/systm.h>
  42
  43 #include <security/mac/mac_framework.h>
  44
  45 /*
  46  * `suser_enabled' (which can be set by the security.bsd.suser_enabled
  47  * sysctl) determines whether the system 'super-user' policy is in effect.  If
  48  * it is nonzero, an effective uid of 0 connotes special privilege,
  49  * overriding many mandatory and discretionary protections.  If it is zero,
  50  * uid 0 is offered no special privilege in the kernel security policy.
  51  * Setting it to zero may seriously impact the functionality of many existing
  52  * userland programs, and should not be done without careful consideration of
  53  * the consequences.
  54  */
  55 static int      suser_enabled = 1;
  56 SYSCTL_INT(_security_bsd, OID_AUTO, suser_enabled, CTLFLAG_RW,
  57     &suser_enabled, 0, "processes with uid 0 have privilege");
  58 TUNABLE_INT("security.bsd.suser_enabled", &suser_enabled);
  59
  60 /*
  61  * Check a credential for privilege.  Lots of good reasons to deny privilege;
  62  * only a few to grant it.
  63  */
  64 int
  65 priv_check_cred(struct ucred *cred, int priv, int flags)
  66 {
  67         int error;
  68
  69         KASSERT(PRIV_VALID(priv), ("priv_check_cred: invalid privilege %d",
  70             priv));
  71
  72         /*
  73          * We first evaluate policies that may deny the granting of
  74          * privilege unilaterally.
  75          */
  76 #ifdef MAC
  77         error = mac_priv_check(cred, priv);
  78         if (error)
  79                 return (error);
  80 #endif
  81
  82         /*
  83          * Jail policy will restrict certain privileges that may otherwise be
  84          * be granted.
  85          */
  86         error = prison_priv_check(cred, priv);
  87         if (error)
  88                 return (error);
  89
  90         /*
  91          * Having determined if privilege is restricted by various policies,
  92          * now determine if privilege is granted.  At this point, any policy
  93          * may grant privilege.  For now, we allow short-circuit boolean
  94          * evaluation, so may not call all policies.  Perhaps we should.
  95          *
  96          * Superuser policy grants privilege based on the effective (or in
  97          * the case of specific privileges, real) uid being 0.  We allow the
  98          * superuser policy to be globally disabled, although this is
  99          * currenty of limited utility.
 100          */
 101         if (suser_enabled) {
 102                 switch (priv) {
 103                 case PRIV_MAXFILES:
 104                 case PRIV_MAXPROC:
 105                 case PRIV_PROC_LIMIT:
 106                         if (cred->cr_ruid == 0)
 107                                 return (0);
 108                         break;
 109
 110                 default:
 111                         if (cred->cr_uid == 0)
 112                                 return (0);
 113                         break;
 114                 }
 115         }
 116
 117         /*
 118          * Now check with MAC, if enabled, to see if a policy module grants
 119          * privilege.
 120          */
 121 #ifdef MAC
 122         if (mac_priv_grant(cred, priv) == 0)
 123                 return (0);
 124 #endif
 125         return (EPERM);
 126 }
 127
 128 int
 129 priv_check(struct thread *td, int priv)
 130 {
 131
 132         KASSERT(td == curthread, ("priv_check: td != curthread"));
 133
 134         return (priv_check_cred(td->td_ucred, priv, 0));
 135 }
 136
 137 /*
 138  * Historical suser() wrapper functions, which now simply request PRIV_ROOT.
 139  * These will be removed in the near future, and exist solely because
 140  * the kernel and modules are not yet fully adapted to the new model.
 141  */
 142 int
 143 suser_cred(struct ucred *cred, int flags)
 144 {
 145
 146         return (priv_check_cred(cred, PRIV_ROOT, flags));
 147 }
 148
 149 int
 150 suser(struct thread *td)
 151 {
 152
 153         KASSERT(td == curthread, ("suser: td != curthread"));
 154
 155         return (suser_cred(td->td_ucred, 0));
 156 }