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 __read_mostly 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 static __always_inline int 75 priv_check_cred_pre(struct ucred *cred, int priv) 76 { 77 int error; 78 79 #ifdef MAC 80 error = mac_priv_check(cred, priv); 81 #else 82 error = 0; 83 #endif 84 return (error); 85 } 86 87 static __always_inline int 88 priv_check_cred_post(struct ucred *cred, int priv, int error, bool handled) 89 { 90 91 if (__predict_true(handled)) 92 goto out; 93 /* 94 * Now check with MAC, if enabled, to see if a policy module grants 95 * privilege. 96 */ 97 #ifdef MAC 98 if (mac_priv_grant(cred, priv) == 0) { 99 error = 0; 100 goto out; 101 } 102 #endif 103 104 /* 105 * The default is deny, so if no policies have granted it, reject 106 * with a privilege error here. 107 */ 108 error = EPERM; 109 out: 110 if (SDT_PROBES_ENABLED()) { 111 if (error) 112 SDT_PROBE1(priv, kernel, priv_check, priv__err, priv); 113 else 114 SDT_PROBE1(priv, kernel, priv_check, priv__ok, priv); 115 } 116 return (error); 117 } 118 119 /* 120 * Check a credential for privilege. Lots of good reasons to deny privilege; 121 * only a few to grant it. 122 */ 123 int 124 priv_check_cred(struct ucred *cred, int priv) 125 { 126 int error; 127 128 KASSERT(PRIV_VALID(priv), ("priv_check_cred: invalid privilege %d", 129 priv)); 130 131 switch (priv) { 132 case PRIV_VFS_GENERATION: 133 return (priv_check_cred_vfs_generation(cred)); 134 } 135 136 /* 137 * We first evaluate policies that may deny the granting of 138 * privilege unilaterally. 139 */ 140 error = priv_check_cred_pre(cred, priv); 141 if (error) 142 goto out; 143 144 /* 145 * Jail policy will restrict certain privileges that may otherwise be 146 * be granted. 147 */ 148 error = prison_priv_check(cred, priv); 149 if (error) 150 goto out; 151 152 if (unprivileged_mlock) { 153 /* 154 * Allow unprivileged users to call mlock(2)/munlock(2) and 155 * mlockall(2)/munlockall(2). 156 */ 157 switch (priv) { 158 case PRIV_VM_MLOCK: 159 case PRIV_VM_MUNLOCK: 160 error = 0; 161 goto out; 162 } 163 } 164 165 if (unprivileged_read_msgbuf) { 166 /* 167 * Allow an unprivileged user to read the kernel message 168 * buffer. 169 */ 170 if (priv == PRIV_MSGBUF) { 171 error = 0; 172 goto out; 173 } 174 } 175 176 /* 177 * Having determined if privilege is restricted by various policies, 178 * now determine if privilege is granted. At this point, any policy 179 * may grant privilege. For now, we allow short-circuit boolean 180 * evaluation, so may not call all policies. Perhaps we should. 181 * 182 * Superuser policy grants privilege based on the effective (or in 183 * the case of specific privileges, real) uid being 0. We allow the 184 * superuser policy to be globally disabled, although this is 185 * currenty of limited utility. 186 */ 187 if (suser_enabled) { 188 switch (priv) { 189 case PRIV_MAXFILES: 190 case PRIV_MAXPROC: 191 case PRIV_PROC_LIMIT: 192 if (cred->cr_ruid == 0) { 193 error = 0; 194 goto out; 195 } 196 break; 197 case PRIV_VFS_READ_DIR: 198 /* 199 * Allow PRIV_VFS_READ_DIR for root if we're not in a 200 * jail, otherwise deny unless a MAC policy grants it. 201 */ 202 if (jailed(cred)) 203 break; 204 /* FALLTHROUGH */ 205 default: 206 if (cred->cr_uid == 0) { 207 error = 0; 208 goto out; 209 } 210 break; 211 } 212 } 213 214 /* 215 * Writes to kernel/physical memory are a typical root-only operation, 216 * but non-root users are expected to be able to read it (provided they 217 * have permission to access /dev/[k]mem). 218 */ 219 if (priv == PRIV_KMEM_READ) { 220 error = 0; 221 goto out; 222 } 223 224 /* 225 * Allow unprivileged process debugging on a per-jail basis. 226 * Do this here instead of prison_priv_check(), so it can also 227 * apply to prison0. 228 */ 229 if (priv == PRIV_DEBUG_UNPRIV) { 230 if (prison_allow(cred, PR_ALLOW_UNPRIV_DEBUG)) { 231 error = 0; 232 goto out; 233 } 234 } 235 236 return (priv_check_cred_post(cred, priv, error, false)); 237 out: 238 return (priv_check_cred_post(cred, priv, error, true)); 239 } 240 241 int 242 priv_check(struct thread *td, int priv) 243 { 244 245 KASSERT(td == curthread, ("priv_check: td != curthread")); 246 247 return (priv_check_cred(td->td_ucred, priv)); 248 } 249 250 int 251 priv_check_cred_vfs_generation(struct ucred *cred) 252 { 253 int error; 254 255 error = priv_check_cred_pre(cred, PRIV_VFS_GENERATION); 256 if (error) 257 goto out; 258 259 if (jailed(cred)) { 260 error = EPERM; 261 goto out; 262 } 263 264 if (cred->cr_uid == 0 && suser_enabled) { 265 error = 0; 266 goto out; 267 } 268 269 return (priv_check_cred_post(cred, PRIV_VFS_GENERATION, error, false)); 270 out: 271 return (priv_check_cred_post(cred, PRIV_VFS_GENERATION, error, true)); 272 273 } 274