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 #include "opt_mac.h" 33 34 #include <sys/cdefs.h> 35 __FBSDID("$FreeBSD$"); 36 37 #include <sys/param.h> 38 #include <sys/jail.h> 39 #include <sys/kernel.h> 40 #include <sys/priv.h> 41 #include <sys/proc.h> 42 #include <sys/sdt.h> 43 #include <sys/sysctl.h> 44 #include <sys/systm.h> 45 46 #include <security/mac/mac_framework.h> 47 48 /* 49 * `suser_enabled' (which can be set by the security.bsd.suser_enabled 50 * sysctl) determines whether the system 'super-user' policy is in effect. If 51 * it is nonzero, an effective uid of 0 connotes special privilege, 52 * overriding many mandatory and discretionary protections. If it is zero, 53 * uid 0 is offered no special privilege in the kernel security policy. 54 * Setting it to zero may seriously impact the functionality of many existing 55 * userland programs, and should not be done without careful consideration of 56 * the consequences. 57 */ 58 static int suser_enabled = 1; 59 SYSCTL_INT(_security_bsd, OID_AUTO, suser_enabled, CTLFLAG_RW, 60 &suser_enabled, 0, "processes with uid 0 have privilege"); 61 TUNABLE_INT("security.bsd.suser_enabled", &suser_enabled); 62 63 SDT_PROVIDER_DEFINE(priv); 64 65 SDT_PROBE_DEFINE(priv, kernel, priv_check, priv_ok); 66 SDT_PROBE_ARGTYPE(priv, kernel, priv_check, priv_ok, 0, "int"); 67 68 SDT_PROBE_DEFINE(priv, kernel, priv_check, priv_err); 69 SDT_PROBE_ARGTYPE(priv, kernel, priv_check, priv_err, 0, "int"); 70 71 /* 72 * Check a credential for privilege. Lots of good reasons to deny privilege; 73 * only a few to grant it. 74 */ 75 int 76 priv_check_cred(struct ucred *cred, int priv, int flags) 77 { 78 int error; 79 80 KASSERT(PRIV_VALID(priv), ("priv_check_cred: invalid privilege %d", 81 priv)); 82 83 /* 84 * We first evaluate policies that may deny the granting of 85 * privilege unilaterally. 86 */ 87 #ifdef MAC 88 error = mac_priv_check(cred, priv); 89 if (error) 90 goto out; 91 #endif 92 93 /* 94 * Jail policy will restrict certain privileges that may otherwise be 95 * be granted. 96 */ 97 error = prison_priv_check(cred, priv); 98 if (error) 99 goto out; 100 101 /* 102 * Having determined if privilege is restricted by various policies, 103 * now determine if privilege is granted. At this point, any policy 104 * may grant privilege. For now, we allow short-circuit boolean 105 * evaluation, so may not call all policies. Perhaps we should. 106 * 107 * Superuser policy grants privilege based on the effective (or in 108 * the case of specific privileges, real) uid being 0. We allow the 109 * superuser policy to be globally disabled, although this is 110 * currenty of limited utility. 111 */ 112 if (suser_enabled) { 113 switch (priv) { 114 case PRIV_MAXFILES: 115 case PRIV_MAXPROC: 116 case PRIV_PROC_LIMIT: 117 if (cred->cr_ruid == 0) { 118 error = 0; 119 goto out; 120 } 121 break; 122 123 default: 124 if (cred->cr_uid == 0) { 125 error = 0; 126 goto out; 127 } 128 break; 129 } 130 } 131 132 /* 133 * Now check with MAC, if enabled, to see if a policy module grants 134 * privilege. 135 */ 136 #ifdef MAC 137 if (mac_priv_grant(cred, priv) == 0) { 138 error = 0; 139 goto out; 140 } 141 #endif 142 143 /* 144 * The default is deny, so if no policies have granted it, reject 145 * with a privilege error here. 146 */ 147 error = EPERM; 148 out: 149 if (error) { 150 SDT_PROBE(priv, kernel, priv_check, priv_err, priv, 0, 0, 0, 151 0); 152 } else { 153 SDT_PROBE(priv, kernel, priv_check, priv_ok, priv, 0, 0, 0, 154 0); 155 } 156 return (error); 157 } 158 159 int 160 priv_check(struct thread *td, int priv) 161 { 162 163 KASSERT(td == curthread, ("priv_check: td != curthread")); 164 165 return (priv_check_cred(td->td_ucred, priv, 0)); 166 } 167