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 <sys/cdefs.h> 32 __FBSDID("$FreeBSD$"); 33 34 #include <sys/param.h> 35 #include <sys/jail.h> 36 #include <sys/kernel.h> 37 #include <sys/priv.h> 38 #include <sys/proc.h> 39 #include <sys/sdt.h> 40 #include <sys/sysctl.h> 41 #include <sys/systm.h> 42 43 #include <security/mac/mac_framework.h> 44 45 /* 46 * `suser_enabled' (which can be set by the security.bsd.suser_enabled 47 * sysctl) determines whether the system 'super-user' policy is in effect. If 48 * it is nonzero, an effective uid of 0 connotes special privilege, 49 * overriding many mandatory and discretionary protections. If it is zero, 50 * uid 0 is offered no special privilege in the kernel security policy. 51 * Setting it to zero may seriously impact the functionality of many existing 52 * userland programs, and should not be done without careful consideration of 53 * the consequences. 54 */ 55 static int suser_enabled = 1; 56 SYSCTL_INT(_security_bsd, OID_AUTO, suser_enabled, CTLFLAG_RWTUN, 57 &suser_enabled, 0, "processes with uid 0 have privilege"); 58 59 static int unprivileged_mlock = 1; 60 SYSCTL_INT(_security_bsd, OID_AUTO, unprivileged_mlock, CTLFLAG_RWTUN, 61 &unprivileged_mlock, 0, "Allow non-root users to call mlock(2)"); 62 63 SDT_PROVIDER_DEFINE(priv); 64 SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv__ok, "int"); 65 SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv__err, "int"); 66 67 /* 68 * Check a credential for privilege. Lots of good reasons to deny privilege; 69 * only a few to grant it. 70 */ 71 int 72 priv_check_cred(struct ucred *cred, int priv, int flags) 73 { 74 int error; 75 76 KASSERT(PRIV_VALID(priv), ("priv_check_cred: invalid privilege %d", 77 priv)); 78 79 /* 80 * We first evaluate policies that may deny the granting of 81 * privilege unilaterally. 82 */ 83 #ifdef MAC 84 error = mac_priv_check(cred, priv); 85 if (error) 86 goto out; 87 #endif 88 89 /* 90 * Jail policy will restrict certain privileges that may otherwise be 91 * be granted. 92 */ 93 error = prison_priv_check(cred, priv); 94 if (error) 95 goto out; 96 97 if (unprivileged_mlock) { 98 /* 99 * Allow unprivileged users to call mlock(2)/munlock(2) and 100 * mlockall(2)/munlockall(2). 101 */ 102 switch (priv) { 103 case PRIV_VM_MLOCK: 104 case PRIV_VM_MUNLOCK: 105 error = 0; 106 goto out; 107 } 108 } 109 110 /* 111 * Having determined if privilege is restricted by various policies, 112 * now determine if privilege is granted. At this point, any policy 113 * may grant privilege. For now, we allow short-circuit boolean 114 * evaluation, so may not call all policies. Perhaps we should. 115 * 116 * Superuser policy grants privilege based on the effective (or in 117 * the case of specific privileges, real) uid being 0. We allow the 118 * superuser policy to be globally disabled, although this is 119 * currenty of limited utility. 120 */ 121 if (suser_enabled) { 122 switch (priv) { 123 case PRIV_MAXFILES: 124 case PRIV_MAXPROC: 125 case PRIV_PROC_LIMIT: 126 if (cred->cr_ruid == 0) { 127 error = 0; 128 goto out; 129 } 130 break; 131 default: 132 if (cred->cr_uid == 0) { 133 error = 0; 134 goto out; 135 } 136 break; 137 } 138 } 139 140 /* 141 * Writes to kernel/physical memory are a typical root-only operation, 142 * but non-root users are expected to be able to read it (provided they 143 * have permission to access /dev/[k]mem). 144 */ 145 if (priv == PRIV_KMEM_READ) { 146 error = 0; 147 goto out; 148 } 149 150 /* 151 * Now check with MAC, if enabled, to see if a policy module grants 152 * privilege. 153 */ 154 #ifdef MAC 155 if (mac_priv_grant(cred, priv) == 0) { 156 error = 0; 157 goto out; 158 } 159 #endif 160 161 /* 162 * The default is deny, so if no policies have granted it, reject 163 * with a privilege error here. 164 */ 165 error = EPERM; 166 out: 167 if (error) 168 SDT_PROBE1(priv, kernel, priv_check, priv__err, priv); 169 else 170 SDT_PROBE1(priv, kernel, priv_check, priv__ok, priv); 171 return (error); 172 } 173 174 int 175 priv_check(struct thread *td, int priv) 176 { 177 178 KASSERT(td == curthread, ("priv_check: td != curthread")); 179 180 return (priv_check_cred(td->td_ucred, priv, 0)); 181 } 182