1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD 3 * 4 * Copyright (c) 2006 nCircle Network Security, Inc. 5 * Copyright (c) 2009 Robert N. M. Watson 6 * All rights reserved. 7 * 8 * This software was developed by Robert N. M. Watson for the TrustedBSD 9 * Project under contract to nCircle Network Security, Inc. 10 * 11 * Redistribution and use in source and binary forms, with or without 12 * modification, are permitted provided that the following conditions 13 * are met: 14 * 1. Redistributions of source code must retain the above copyright 15 * notice, this list of conditions and the following disclaimer. 16 * 2. Redistributions in binary form must reproduce the above copyright 17 * notice, this list of conditions and the following disclaimer in the 18 * documentation and/or other materials provided with the distribution. 19 * 20 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR, NCIRCLE NETWORK SECURITY, 24 * INC., OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 25 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED 26 * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR 27 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF 28 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING 29 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS 30 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 31 */ 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_RWTUN, 59 &suser_enabled, 0, "processes with uid 0 have privilege"); 60 61 static int unprivileged_mlock = 1; 62 SYSCTL_INT(_security_bsd, OID_AUTO, unprivileged_mlock, CTLFLAG_RWTUN, 63 &unprivileged_mlock, 0, "Allow non-root users to call mlock(2)"); 64 65 static int unprivileged_read_msgbuf = 1; 66 SYSCTL_INT(_security_bsd, OID_AUTO, unprivileged_read_msgbuf, 67 CTLFLAG_RW, &unprivileged_read_msgbuf, 0, 68 "Unprivileged processes may read the kernel message buffer"); 69 70 SDT_PROVIDER_DEFINE(priv); 71 SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv__ok, "int"); 72 SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv__err, "int"); 73 74 /* 75 * Check a credential for privilege. Lots of good reasons to deny privilege; 76 * only a few to grant it. 77 */ 78 int 79 priv_check_cred(struct ucred *cred, int priv) 80 { 81 int error; 82 83 KASSERT(PRIV_VALID(priv), ("priv_check_cred: invalid privilege %d", 84 priv)); 85 86 /* 87 * We first evaluate policies that may deny the granting of 88 * privilege unilaterally. 89 */ 90 #ifdef MAC 91 error = mac_priv_check(cred, priv); 92 if (error) 93 goto out; 94 #endif 95 96 /* 97 * Jail policy will restrict certain privileges that may otherwise be 98 * be granted. 99 */ 100 error = prison_priv_check(cred, priv); 101 if (error) 102 goto out; 103 104 if (unprivileged_mlock) { 105 /* 106 * Allow unprivileged users to call mlock(2)/munlock(2) and 107 * mlockall(2)/munlockall(2). 108 */ 109 switch (priv) { 110 case PRIV_VM_MLOCK: 111 case PRIV_VM_MUNLOCK: 112 error = 0; 113 goto out; 114 } 115 } 116 117 if (unprivileged_read_msgbuf) { 118 /* 119 * Allow an unprivileged user to read the kernel message 120 * buffer. 121 */ 122 if (priv == PRIV_MSGBUF) { 123 error = 0; 124 goto out; 125 } 126 } 127 128 /* 129 * Having determined if privilege is restricted by various policies, 130 * now determine if privilege is granted. At this point, any policy 131 * may grant privilege. For now, we allow short-circuit boolean 132 * evaluation, so may not call all policies. Perhaps we should. 133 * 134 * Superuser policy grants privilege based on the effective (or in 135 * the case of specific privileges, real) uid being 0. We allow the 136 * superuser policy to be globally disabled, although this is 137 * currenty of limited utility. 138 */ 139 if (suser_enabled) { 140 switch (priv) { 141 case PRIV_MAXFILES: 142 case PRIV_MAXPROC: 143 case PRIV_PROC_LIMIT: 144 if (cred->cr_ruid == 0) { 145 error = 0; 146 goto out; 147 } 148 break; 149 default: 150 if (cred->cr_uid == 0) { 151 error = 0; 152 goto out; 153 } 154 break; 155 } 156 } 157 158 /* 159 * Writes to kernel/physical memory are a typical root-only operation, 160 * but non-root users are expected to be able to read it (provided they 161 * have permission to access /dev/[k]mem). 162 */ 163 if (priv == PRIV_KMEM_READ) { 164 error = 0; 165 goto out; 166 } 167 168 /* 169 * Allow unprivileged process debugging on a per-jail basis. 170 * Do this here instead of prison_priv_check(), so it can also 171 * apply to prison0. 172 */ 173 if (priv == PRIV_DEBUG_UNPRIV) { 174 if (prison_allow(cred, PR_ALLOW_UNPRIV_DEBUG)) { 175 error = 0; 176 goto out; 177 } 178 } 179 180 /* 181 * Now check with MAC, if enabled, to see if a policy module grants 182 * privilege. 183 */ 184 #ifdef MAC 185 if (mac_priv_grant(cred, priv) == 0) { 186 error = 0; 187 goto out; 188 } 189 #endif 190 191 /* 192 * The default is deny, so if no policies have granted it, reject 193 * with a privilege error here. 194 */ 195 error = EPERM; 196 out: 197 if (SDT_PROBES_ENABLED()) { 198 if (error) 199 SDT_PROBE1(priv, kernel, priv_check, priv__err, priv); 200 else 201 SDT_PROBE1(priv, kernel, priv_check, priv__ok, priv); 202 } 203 return (error); 204 } 205 206 int 207 priv_check(struct thread *td, int priv) 208 { 209 210 KASSERT(td == curthread, ("priv_check: td != curthread")); 211 212 return (priv_check_cred(td->td_ucred, priv)); 213 } 214