The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_priv.c

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    1 /*-
    2  * Copyright (c) 2006 nCircle Network Security, Inc.
    3  * Copyright (c) 2009 Robert N. M. Watson
    4  * All rights reserved.
    5  *
    6  * This software was developed by Robert N. M. Watson for the TrustedBSD
    7  * Project under contract to nCircle Network Security, Inc.
    8  *
    9  * Redistribution and use in source and binary forms, with or without
   10  * modification, are permitted provided that the following conditions
   11  * are met:
   12  * 1. Redistributions of source code must retain the above copyright
   13  *    notice, this list of conditions and the following disclaimer.
   14  * 2. Redistributions in binary form must reproduce the above copyright
   15  *    notice, this list of conditions and the following disclaimer in the
   16  *    documentation and/or other materials provided with the distribution.
   17  *
   18  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   19  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   20  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   21  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR, NCIRCLE NETWORK SECURITY,
   22  * INC., OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   23  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
   24  * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
   25  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
   26  * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
   27  * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
   28  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   29  */
   30 
   31 #include "opt_kdtrace.h"
   32 
   33 #include <sys/cdefs.h>
   34 __FBSDID("$FreeBSD$");
   35 
   36 #include <sys/param.h>
   37 #include <sys/jail.h>
   38 #include <sys/kernel.h>
   39 #include <sys/priv.h>
   40 #include <sys/proc.h>
   41 #include <sys/sdt.h>
   42 #include <sys/sysctl.h>
   43 #include <sys/systm.h>
   44 
   45 #include <security/mac/mac_framework.h>
   46 
   47 /*
   48  * `suser_enabled' (which can be set by the security.bsd.suser_enabled
   49  * sysctl) determines whether the system 'super-user' policy is in effect.  If
   50  * it is nonzero, an effective uid of 0 connotes special privilege,
   51  * overriding many mandatory and discretionary protections.  If it is zero,
   52  * uid 0 is offered no special privilege in the kernel security policy.
   53  * Setting it to zero may seriously impact the functionality of many existing
   54  * userland programs, and should not be done without careful consideration of
   55  * the consequences. 
   56  */
   57 static int      suser_enabled = 1;
   58 SYSCTL_INT(_security_bsd, OID_AUTO, suser_enabled, CTLFLAG_RW,
   59     &suser_enabled, 0, "processes with uid 0 have privilege");
   60 TUNABLE_INT("security.bsd.suser_enabled", &suser_enabled);
   61 
   62 SDT_PROVIDER_DEFINE(priv);
   63 SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv_ok, priv-ok, "int");
   64 SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv_err, priv-err, "int");
   65 
   66 /*
   67  * Check a credential for privilege.  Lots of good reasons to deny privilege;
   68  * only a few to grant it.
   69  */
   70 int
   71 priv_check_cred(struct ucred *cred, int priv, int flags)
   72 {
   73         int error;
   74 
   75         KASSERT(PRIV_VALID(priv), ("priv_check_cred: invalid privilege %d",
   76             priv));
   77 
   78         /*
   79          * We first evaluate policies that may deny the granting of
   80          * privilege unilaterally.
   81          */
   82 #ifdef MAC
   83         error = mac_priv_check(cred, priv);
   84         if (error)
   85                 goto out;
   86 #endif
   87 
   88         /*
   89          * Jail policy will restrict certain privileges that may otherwise be
   90          * be granted.
   91          */
   92         error = prison_priv_check(cred, priv);
   93         if (error)
   94                 goto out;
   95 
   96         /*
   97          * Having determined if privilege is restricted by various policies,
   98          * now determine if privilege is granted.  At this point, any policy
   99          * may grant privilege.  For now, we allow short-circuit boolean
  100          * evaluation, so may not call all policies.  Perhaps we should.
  101          *
  102          * Superuser policy grants privilege based on the effective (or in
  103          * the case of specific privileges, real) uid being 0.  We allow the
  104          * superuser policy to be globally disabled, although this is
  105          * currenty of limited utility.
  106          */
  107         if (suser_enabled) {
  108                 switch (priv) {
  109                 case PRIV_MAXFILES:
  110                 case PRIV_MAXPROC:
  111                 case PRIV_PROC_LIMIT:
  112                         if (cred->cr_ruid == 0) {
  113                                 error = 0;
  114                                 goto out;
  115                         }
  116                         break;
  117 
  118                 default:
  119                         if (cred->cr_uid == 0) {
  120                                 error = 0;
  121                                 goto out;
  122                         }
  123                         break;
  124                 }
  125         }
  126 
  127         /*
  128          * Now check with MAC, if enabled, to see if a policy module grants
  129          * privilege.
  130          */
  131 #ifdef MAC
  132         if (mac_priv_grant(cred, priv) == 0) {
  133                 error = 0;
  134                 goto out;
  135         }
  136 #endif
  137 
  138         /*
  139          * The default is deny, so if no policies have granted it, reject
  140          * with a privilege error here.
  141          */
  142         error = EPERM;
  143 out:
  144         if (error) {
  145                 SDT_PROBE(priv, kernel, priv_check, priv_err, priv, 0, 0, 0,
  146                     0);
  147         } else {
  148                 SDT_PROBE(priv, kernel, priv_check, priv_ok, priv, 0, 0, 0,
  149                     0);
  150         }
  151         return (error);
  152 }
  153 
  154 int
  155 priv_check(struct thread *td, int priv)
  156 {
  157 
  158         KASSERT(td == curthread, ("priv_check: td != curthread"));
  159 
  160         return (priv_check_cred(td->td_ucred, priv, 0));
  161 }

Cache object: 98487a15f065d52b570bd531f688e084


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