1 /* 2 * CDDL HEADER START 3 * 4 * The contents of this file are subject to the terms of the 5 * Common Development and Distribution License (the "License"). 6 * You may not use this file except in compliance with the License. 7 * 8 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE 9 * or http://www.opensolaris.org/os/licensing. 10 * See the License for the specific language governing permissions 11 * and limitations under the License. 12 * 13 * When distributing Covered Code, include this CDDL HEADER in each 14 * file and include the License file at usr/src/OPENSOLARIS.LICENSE. 15 * If applicable, add the following below this CDDL HEADER, with the 16 * fields enclosed by brackets "[]" replaced with your own identifying 17 * information: Portions Copyright [yyyy] [name of copyright owner] 18 * 19 * CDDL HEADER END 20 */ 21 22 /* 23 * Copyright 2008 Sun Microsystems, Inc. All rights reserved. 24 * Use is subject to license terms. 25 */ 26 27 /* 28 * dns_mt.c 29 * 30 * This file contains all the MT related routines for the DNS backend. 31 */ 32 33 #include "dns_common.h" 34 #include <dlfcn.h> 35 36 /* 37 * If the DNS name service switch routines are used in a binary that depends 38 * on an older libresolv (libresolv.so.1, say), then having nss_dns.so.1 or 39 * libnss_dns.a depend on a newer libresolv (libresolv.so.2) will cause 40 * relocation problems. In particular, copy relocation of the _res structure 41 * (which changes in size from libresolv.so.1 to libresolv.so.2) could 42 * cause corruption, and result in a number of strange problems, including 43 * core dumps. Hence, we check if a libresolv is already loaded. 44 */ 45 46 #pragma init(_nss_dns_init) 47 static void _nss_dns_init(void); 48 49 extern struct hostent *res_gethostbyname(const char *); 50 #pragma weak res_gethostbyname 51 52 #define RES_SET_NO_HOSTS_FALLBACK "__res_set_no_hosts_fallback" 53 extern void __res_set_no_hosts_fallback(void); 54 #pragma weak __res_set_no_hosts_fallback 55 56 #define RES_UNSET_NO_HOSTS_FALLBACK "__res_unset_no_hosts_fallback" 57 extern void __res_unset_no_hosts_fallback(void); 58 #pragma weak __res_unset_no_hosts_fallback 59 60 #define RES_GET_RES "__res_get_res" 61 extern struct __res_state *__res_get_res(void); 62 #pragma weak __res_get_res 63 64 #define RES_ENABLE_MT "__res_enable_mt" 65 extern int __res_enable_mt(void); 66 #pragma weak __res_enable_mt 67 68 #define RES_DISABLE_MT "__res_disable_mt" 69 extern int __res_disable_mt(void); 70 #pragma weak __res_disable_mt 71 72 #define RES_GET_H_ERRNO "__res_get_h_errno" 73 extern int *__res_get_h_errno(); 74 #pragma weak __res_get_h_errno 75 76 #define __H_ERRNO "__h_errno" 77 extern int *__h_errno(void); 78 #pragma weak __h_errno 79 80 #define RES_OVERRIDE_RETRY "__res_override_retry" 81 extern int __res_override_retry(int); 82 #pragma weak __res_override_retry 83 84 static void __fallback_set_no_hosts(void); 85 static int *__fallback_h_errno(void); 86 static int __fallback_override_retry(int); 87 static int __is_mt_safe(void); 88 89 void (*set_no_hosts_fallback)(void) = __fallback_set_no_hosts; 90 void (*unset_no_hosts_fallback)(void) = __fallback_set_no_hosts; 91 struct __res_state *(*set_res_retry)() = 0; 92 int (*enable_mt)() = 0; 93 int (*disable_mt)() = 0; 94 int *(*get_h_errno)(void) = 0; 95 int (*override_retry)(int) = 0; 96 97 /* Usually set from the Makefile */ 98 #ifndef NSS_DNS_LIBRESOLV 99 #define NSS_DNS_LIBRESOLV "libresolv.so.2" 100 #endif 101 102 /* From libresolv */ 103 extern int h_errno; 104 105 mutex_t one_lane = DEFAULTMUTEX; 106 107 void 108 _nss_dns_init(void) 109 { 110 void *reslib, (*f_void_ptr)(); 111 112 /* If no libresolv library, then load one */ 113 if (res_gethostbyname == 0) { 114 if ((reslib = 115 dlopen(NSS_DNS_LIBRESOLV, RTLD_LAZY|RTLD_GLOBAL)) != 0) { 116 /* Turn off /etc/hosts fall back in libresolv */ 117 if ((f_void_ptr = (void (*)(void))dlsym(reslib, 118 RES_SET_NO_HOSTS_FALLBACK)) != 0) { 119 set_no_hosts_fallback = f_void_ptr; 120 } 121 if ((f_void_ptr = (void (*)(void))dlsym(reslib, 122 RES_SET_NO_HOSTS_FALLBACK)) != 0) { 123 unset_no_hosts_fallback = f_void_ptr; 124 } 125 /* Set number of resolver retries */ 126 if ((override_retry = (int (*)(int))dlsym(reslib, 127 RES_OVERRIDE_RETRY)) == 0) { 128 set_res_retry = 129 (struct __res_state *(*)(void))dlsym(reslib, 130 RES_GET_RES); 131 override_retry = __fallback_override_retry; 132 } 133 /* 134 * Select h_errno retrieval function. A BIND 8.2.2 135 * libresolv.so.2 will have __h_errno, a BIND 8.1.2 136 * one will have __res_get_h_errno, and other 137 * versions may have nothing at all. 138 * 139 * Also try to bind to the relevant MT enable/disable 140 * functions which are also dependent on the version 141 * of the BIND libresolv.so.2 being used. 142 */ 143 if ((get_h_errno = (int *(*)(void))dlsym(reslib, 144 __H_ERRNO)) != 0) { 145 /* BIND 8.2.2 libresolv.so.2 is MT safe. */ 146 enable_mt = __is_mt_safe; 147 disable_mt = __is_mt_safe; 148 } else { 149 if ((get_h_errno = 150 (int *(*)(void))dlsym(reslib, 151 RES_GET_H_ERRNO)) == 0) { 152 get_h_errno = __fallback_h_errno; 153 } 154 /* 155 * Pre-BIND 8.2.2 was not MT safe. Try to 156 * bind the MT enable/disable functions. 157 */ 158 if ((enable_mt = (int (*)(void))dlsym(reslib, 159 RES_ENABLE_MT)) != 0 && 160 (disable_mt = (int (*)(void))dlsym(reslib, 161 RES_DISABLE_MT)) == 0) { 162 enable_mt = 0; 163 } 164 } 165 } 166 } else { 167 /* Libresolv already loaded */ 168 if ((f_void_ptr = __res_set_no_hosts_fallback) != 0) { 169 set_no_hosts_fallback = f_void_ptr; 170 } 171 if ((f_void_ptr = __res_unset_no_hosts_fallback) != 0) { 172 unset_no_hosts_fallback = f_void_ptr; 173 } 174 if ((override_retry = __res_override_retry) == 0) { 175 set_res_retry = __res_get_res; 176 override_retry = __fallback_override_retry; 177 } 178 if ((get_h_errno = __h_errno) == 0 && 179 (get_h_errno = __res_get_h_errno) == 0) { 180 get_h_errno = __fallback_h_errno; 181 } 182 if (get_h_errno == __h_errno) { 183 enable_mt = __is_mt_safe; 184 disable_mt = __is_mt_safe; 185 } else { 186 if ((enable_mt = __res_enable_mt) != 0 && 187 (disable_mt = __res_disable_mt) == 0) { 188 enable_mt = 0; 189 } 190 } 191 } 192 } 193 194 195 /* 196 * 197 * Integration of BIND 8.1.2 introduced two new Sun private functions, 198 * __res_enable_mt() and __res_disable_mt(), that enabled and disabled 199 * MT mode per-thread. These functions are in the private libresolv.so.2 200 * interface, and intended for use by nss_dns.so.1. 201 * 202 * BIND 8.2.2 removed the need for those two functions. As similar 203 * functionality was provided in BIND further up the stack. However the 204 * functions remain to satisfy any application that directly called upon 205 * them. Only, __res_enable_mt() was modified to return failure. 206 * Indicated by a non-zero return value. So that those unconventional 207 * applications would not then presume that res_send() and friends are 208 * MT-safe, when in fact they are not. 209 * 210 * To prevent nss_dns from locking inappropriately __is_mt_safe() is 211 * called in place of __res_enable_mt() and __res_disable_mt() if BIND 212 * 8.2.2 libresolv.so.2 being used. __is_mt_safe() returns success 213 * indicated by a return code of zero. Signifying that no locking is 214 * necessary. 215 * 216 * MT applications making calls to gethostby*_r() or getipnodeby*() 217 * linked to libresolv.so.1 or linked statically with pre-BIND 8.2.2 218 * libresolv.a, doubtful as we don't ship a static version, would require 219 * locking within the nsswitch back-end. Hence the mechanism can not 220 * simply be removed. 221 * 222 */ 223 static int 224 __is_mt_safe(void) { 225 return (0); 226 } 227 228 229 /* 230 * Return pointer to the global h_errno variable 231 */ 232 static int * 233 __fallback_h_errno(void) { 234 return (&h_errno); 235 } 236 237 238 /* 239 * This function is called when the resolver library doesn't provide its 240 * own function to establish an override retry. If we can get a pointer 241 * to the per-thread _res (i.e., set_res_retry != 0), we set the retries 242 * directly, and return the previous number of retries. Otherwise, there's 243 * nothing to do. 244 */ 245 static int 246 __fallback_override_retry(int retry) { 247 struct __res_state *res; 248 int old_retry = 0; 249 250 if (set_res_retry != 0) { 251 res = set_res_retry(); 252 old_retry = res->retry; 253 res->retry = retry; 254 } 255 return (old_retry); 256 } 257 258 259 static void 260 __fallback_set_no_hosts(void) { 261 } 262 263 264 /* 265 * Common code to enable/disable MT mode, set/unset no-/etc/hosts fallback, 266 * and to set the number of retries. 267 */ 268 void 269 switch_resolver_setup(int *mt_disabled, sigset_t *oldmask, int *old_retry) { 270 271 /* 272 * Try to enable MT mode. If that isn't possible, mask signals, 273 * and mutex_lock. 274 */ 275 *mt_disabled = 1; 276 if (enable_mt == 0 || (*mt_disabled = (*enable_mt)()) != 0) { 277 sigset_t newmask; 278 (void) sigfillset(&newmask); 279 (void) thr_sigsetmask(SIG_SETMASK, &newmask, oldmask); 280 (void) mutex_lock(&one_lane); 281 } 282 283 /* 284 * Disable any fallback to /etc/hosts (or /etc/inet/ipnodes, when 285 * libresolv knows about that file). 286 */ 287 (*set_no_hosts_fallback)(); 288 289 /* 290 * The NS switch wants to handle retries on its own. 291 */ 292 *old_retry = (*override_retry)(1); 293 } 294 295 296 void 297 switch_resolver_reset(int mt_disabled, sigset_t oldmask, int old_retry) { 298 299 if (mt_disabled) { 300 (void) mutex_unlock(&one_lane); 301 (void) thr_sigsetmask(SIG_SETMASK, &oldmask, NULL); 302 } else { 303 (void) (*disable_mt)(); 304 } 305 306 (*unset_no_hosts_fallback)(); 307 308 (void) (*override_retry)(old_retry); 309 } 310