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_RW, 57 &suser_enabled, 0, "processes with uid 0 have privilege"); 58 TUNABLE_INT("security.bsd.suser_enabled", &suser_enabled); 59 60 static int unprivileged_mlock = 1; 61 SYSCTL_INT(_security_bsd, OID_AUTO, unprivileged_mlock, CTLFLAG_RW|CTLFLAG_TUN, 62 &unprivileged_mlock, 0, "Allow non-root users to call mlock(2)"); 63 TUNABLE_INT("security.bsd.unprivileged_mlock", &unprivileged_mlock); 64 65 SDT_PROVIDER_DEFINE(priv); 66 SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv__ok, "int"); 67 SDT_PROBE_DEFINE1(priv, kernel, priv_check, priv__err, "int"); 68 69 /* 70 * Check a credential for privilege. Lots of good reasons to deny privilege; 71 * only a few to grant it. 72 */ 73 int 74 priv_check_cred(struct ucred *cred, int priv, int flags) 75 { 76 int error; 77 78 KASSERT(PRIV_VALID(priv), ("priv_check_cred: invalid privilege %d", 79 priv)); 80 81 /* 82 * We first evaluate policies that may deny the granting of 83 * privilege unilaterally. 84 */ 85 #ifdef MAC 86 error = mac_priv_check(cred, priv); 87 if (error) 88 goto out; 89 #endif 90 91 /* 92 * Jail policy will restrict certain privileges that may otherwise be 93 * be granted. 94 */ 95 error = prison_priv_check(cred, priv); 96 if (error) 97 goto out; 98 99 if (unprivileged_mlock) { 100 /* 101 * Allow unprivileged users to call mlock(2)/munlock(2) and 102 * mlockall(2)/munlockall(2). 103 */ 104 switch (priv) { 105 case PRIV_VM_MLOCK: 106 case PRIV_VM_MUNLOCK: 107 error = 0; 108 goto out; 109 } 110 } 111 112 /* 113 * Having determined if privilege is restricted by various policies, 114 * now determine if privilege is granted. At this point, any policy 115 * may grant privilege. For now, we allow short-circuit boolean 116 * evaluation, so may not call all policies. Perhaps we should. 117 * 118 * Superuser policy grants privilege based on the effective (or in 119 * the case of specific privileges, real) uid being 0. We allow the 120 * superuser policy to be globally disabled, although this is 121 * currenty of limited utility. 122 */ 123 if (suser_enabled) { 124 switch (priv) { 125 case PRIV_MAXFILES: 126 case PRIV_MAXPROC: 127 case PRIV_PROC_LIMIT: 128 if (cred->cr_ruid == 0) { 129 error = 0; 130 goto out; 131 } 132 break; 133 default: 134 if (cred->cr_uid == 0) { 135 error = 0; 136 goto out; 137 } 138 break; 139 } 140 } 141 142 /* 143 * Writes to kernel/physical memory are a typical root-only operation, 144 * but non-root users are expected to be able to read it (provided they 145 * have permission to access /dev/[k]mem). 146 */ 147 if (priv == PRIV_KMEM_READ) { 148 error = 0; 149 goto out; 150 } 151 152 /* 153 * Now check with MAC, if enabled, to see if a policy module grants 154 * privilege. 155 */ 156 #ifdef MAC 157 if (mac_priv_grant(cred, priv) == 0) { 158 error = 0; 159 goto out; 160 } 161 #endif 162 163 /* 164 * The default is deny, so if no policies have granted it, reject 165 * with a privilege error here. 166 */ 167 error = EPERM; 168 out: 169 if (error) 170 SDT_PROBE1(priv, kernel, priv_check, priv__err, priv); 171 else 172 SDT_PROBE1(priv, kernel, priv_check, priv__ok, priv); 173 return (error); 174 } 175 176 int 177 priv_check(struct thread *td, int priv) 178 { 179 180 KASSERT(td == curthread, ("priv_check: td != curthread")); 181 182 return (priv_check_cred(td->td_ucred, priv, 0)); 183 } 184