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, "int"); 64 SDT_PROBE_DEFINE1(priv, kernel, priv_check, 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 } 162