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_LOOKUP: 133 return (priv_check_cred_vfs_lookup(cred)); 134 case PRIV_VFS_GENERATION: 135 return (priv_check_cred_vfs_generation(cred)); 136 } 137 138 /* 139 * We first evaluate policies that may deny the granting of 140 * privilege unilaterally. 141 */ 142 error = priv_check_cred_pre(cred, priv); 143 if (error) 144 goto out; 145 146 /* 147 * Jail policy will restrict certain privileges that may otherwise be 148 * be granted. 149 */ 150 error = prison_priv_check(cred, priv); 151 if (error) 152 goto out; 153 154 if (unprivileged_mlock) { 155 /* 156 * Allow unprivileged users to call mlock(2)/munlock(2) and 157 * mlockall(2)/munlockall(2). 158 */ 159 switch (priv) { 160 case PRIV_VM_MLOCK: 161 case PRIV_VM_MUNLOCK: 162 error = 0; 163 goto out; 164 } 165 } 166 167 if (unprivileged_read_msgbuf) { 168 /* 169 * Allow an unprivileged user to read the kernel message 170 * buffer. 171 */ 172 if (priv == PRIV_MSGBUF) { 173 error = 0; 174 goto out; 175 } 176 } 177 178 /* 179 * Having determined if privilege is restricted by various policies, 180 * now determine if privilege is granted. At this point, any policy 181 * may grant privilege. For now, we allow short-circuit boolean 182 * evaluation, so may not call all policies. Perhaps we should. 183 * 184 * Superuser policy grants privilege based on the effective (or in 185 * the case of specific privileges, real) uid being 0. We allow the 186 * superuser policy to be globally disabled, although this is 187 * currenty of limited utility. 188 */ 189 if (suser_enabled) { 190 switch (priv) { 191 case PRIV_MAXFILES: 192 case PRIV_MAXPROC: 193 case PRIV_PROC_LIMIT: 194 if (cred->cr_ruid == 0) { 195 error = 0; 196 goto out; 197 } 198 break; 199 case PRIV_VFS_READ_DIR: 200 /* 201 * Allow PRIV_VFS_READ_DIR for root if we're not in a 202 * jail, otherwise deny unless a MAC policy grants it. 203 */ 204 if (jailed(cred)) 205 break; 206 /* FALLTHROUGH */ 207 default: 208 if (cred->cr_uid == 0) { 209 error = 0; 210 goto out; 211 } 212 break; 213 } 214 } 215 216 /* 217 * Writes to kernel/physical memory are a typical root-only operation, 218 * but non-root users are expected to be able to read it (provided they 219 * have permission to access /dev/[k]mem). 220 */ 221 if (priv == PRIV_KMEM_READ) { 222 error = 0; 223 goto out; 224 } 225 226 /* 227 * Allow unprivileged process debugging on a per-jail basis. 228 * Do this here instead of prison_priv_check(), so it can also 229 * apply to prison0. 230 */ 231 if (priv == PRIV_DEBUG_UNPRIV) { 232 if (prison_allow(cred, PR_ALLOW_UNPRIV_DEBUG)) { 233 error = 0; 234 goto out; 235 } 236 } 237 238 return (priv_check_cred_post(cred, priv, error, false)); 239 out: 240 return (priv_check_cred_post(cred, priv, error, true)); 241 } 242 243 int 244 priv_check(struct thread *td, int priv) 245 { 246 247 KASSERT(td == curthread, ("priv_check: td != curthread")); 248 249 return (priv_check_cred(td->td_ucred, priv)); 250 } 251 252 static int __noinline 253 priv_check_cred_vfs_lookup_slow(struct ucred *cred) 254 { 255 int error; 256 257 error = priv_check_cred_pre(cred, PRIV_VFS_LOOKUP); 258 if (error) 259 goto out; 260 261 if (cred->cr_uid == 0 && suser_enabled) { 262 error = 0; 263 goto out; 264 } 265 266 return (priv_check_cred_post(cred, PRIV_VFS_LOOKUP, error, false)); 267 out: 268 return (priv_check_cred_post(cred, PRIV_VFS_LOOKUP, error, true)); 269 270 } 271 272 int 273 priv_check_cred_vfs_lookup(struct ucred *cred) 274 { 275 int error; 276 277 if (__predict_false(mac_priv_check_fp_flag || 278 mac_priv_grant_fp_flag || SDT_PROBES_ENABLED())) 279 return (priv_check_cred_vfs_lookup_slow(cred)); 280 281 error = EPERM; 282 if (cred->cr_uid == 0 && suser_enabled) 283 error = 0; 284 return (error); 285 } 286 287 int 288 priv_check_cred_vfs_lookup_nomac(struct ucred *cred) 289 { 290 int error; 291 292 if (__predict_false(mac_priv_check_fp_flag || 293 mac_priv_grant_fp_flag || SDT_PROBES_ENABLED())) 294 return (EAGAIN); 295 296 error = EPERM; 297 if (cred->cr_uid == 0 && suser_enabled) 298 error = 0; 299 return (error); 300 } 301 302 static int __noinline 303 priv_check_cred_vfs_generation_slow(struct ucred *cred) 304 { 305 int error; 306 307 error = priv_check_cred_pre(cred, PRIV_VFS_GENERATION); 308 if (error) 309 goto out; 310 311 if (jailed(cred)) { 312 error = EPERM; 313 goto out; 314 } 315 316 if (cred->cr_uid == 0 && suser_enabled) { 317 error = 0; 318 goto out; 319 } 320 321 return (priv_check_cred_post(cred, PRIV_VFS_GENERATION, error, false)); 322 out: 323 return (priv_check_cred_post(cred, PRIV_VFS_GENERATION, error, true)); 324 325 } 326 327 int 328 priv_check_cred_vfs_generation(struct ucred *cred) 329 { 330 int error; 331 332 if (__predict_false(mac_priv_check_fp_flag || 333 mac_priv_grant_fp_flag || SDT_PROBES_ENABLED())) 334 return (priv_check_cred_vfs_generation_slow(cred)); 335 336 error = EPERM; 337 if (!jailed(cred) && cred->cr_uid == 0 && suser_enabled) 338 error = 0; 339 return (error); 340 } 341