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