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 #pragma ident "%Z%%M% %I% %E% SMI" 28 29 /* 30 * dns_mt.c 31 * 32 * This file contains all the MT related routines for the DNS backend. 33 */ 34 35 #include "dns_common.h" 36 #include <dlfcn.h> 37 38 /* 39 * If the DNS name service switch routines are used in a binary that depends 40 * on an older libresolv (libresolv.so.1, say), then having nss_dns.so.1 or 41 * libnss_dns.a depend on a newer libresolv (libresolv.so.2) will cause 42 * relocation problems. In particular, copy relocation of the _res structure 43 * (which changes in size from libresolv.so.1 to libresolv.so.2) could 44 * cause corruption, and result in a number of strange problems, including 45 * core dumps. Hence, we check if a libresolv is already loaded. 46 */ 47 48 #pragma init(_nss_dns_init) 49 static void _nss_dns_init(void); 50 51 extern struct hostent *res_gethostbyname(const char *); 52 #pragma weak res_gethostbyname 53 54 #define RES_SET_NO_HOSTS_FALLBACK "__res_set_no_hosts_fallback" 55 extern void __res_set_no_hosts_fallback(void); 56 #pragma weak __res_set_no_hosts_fallback 57 58 #define RES_UNSET_NO_HOSTS_FALLBACK "__res_unset_no_hosts_fallback" 59 extern void __res_unset_no_hosts_fallback(void); 60 #pragma weak __res_unset_no_hosts_fallback 61 62 #define RES_GET_RES "__res_get_res" 63 extern struct __res_state *__res_get_res(void); 64 #pragma weak __res_get_res 65 66 #define RES_ENABLE_MT "__res_enable_mt" 67 extern int __res_enable_mt(void); 68 #pragma weak __res_enable_mt 69 70 #define RES_DISABLE_MT "__res_disable_mt" 71 extern int __res_disable_mt(void); 72 #pragma weak __res_disable_mt 73 74 #define RES_GET_H_ERRNO "__res_get_h_errno" 75 extern int *__res_get_h_errno(); 76 #pragma weak __res_get_h_errno 77 78 #define __H_ERRNO "__h_errno" 79 extern int *__h_errno(void); 80 #pragma weak __h_errno 81 82 #define RES_OVERRIDE_RETRY "__res_override_retry" 83 extern int __res_override_retry(int); 84 #pragma weak __res_override_retry 85 86 static void __fallback_set_no_hosts(void); 87 static int *__fallback_h_errno(void); 88 static int __fallback_override_retry(int); 89 static int __is_mt_safe(void); 90 91 void (*set_no_hosts_fallback)(void) = __fallback_set_no_hosts; 92 void (*unset_no_hosts_fallback)(void) = __fallback_set_no_hosts; 93 struct __res_state *(*set_res_retry)() = 0; 94 int (*enable_mt)() = 0; 95 int (*disable_mt)() = 0; 96 int *(*get_h_errno)(void) = 0; 97 int (*override_retry)(int) = 0; 98 99 /* Usually set from the Makefile */ 100 #ifndef NSS_DNS_LIBRESOLV 101 #define NSS_DNS_LIBRESOLV "libresolv.so.2" 102 #endif 103 104 /* From libresolv */ 105 extern int h_errno; 106 107 mutex_t one_lane = DEFAULTMUTEX; 108 109 void 110 _nss_dns_init(void) 111 { 112 void *reslib, (*f_void_ptr)(); 113 114 /* If no libresolv library, then load one */ 115 if (res_gethostbyname == 0) { 116 if ((reslib = 117 dlopen(NSS_DNS_LIBRESOLV, RTLD_LAZY|RTLD_GLOBAL)) != 0) { 118 /* Turn off /etc/hosts fall back in libresolv */ 119 if ((f_void_ptr = (void (*)(void))dlsym(reslib, 120 RES_SET_NO_HOSTS_FALLBACK)) != 0) { 121 set_no_hosts_fallback = f_void_ptr; 122 } 123 if ((f_void_ptr = (void (*)(void))dlsym(reslib, 124 RES_SET_NO_HOSTS_FALLBACK)) != 0) { 125 unset_no_hosts_fallback = f_void_ptr; 126 } 127 /* Set number of resolver retries */ 128 if ((override_retry = (int (*)(int))dlsym(reslib, 129 RES_OVERRIDE_RETRY)) == 0) { 130 set_res_retry = 131 (struct __res_state *(*)(void))dlsym(reslib, 132 RES_GET_RES); 133 override_retry = __fallback_override_retry; 134 } 135 /* 136 * Select h_errno retrieval function. A BIND 8.2.2 137 * libresolv.so.2 will have __h_errno, a BIND 8.1.2 138 * one will have __res_get_h_errno, and other 139 * versions may have nothing at all. 140 * 141 * Also try to bind to the relevant MT enable/disable 142 * functions which are also dependent on the version 143 * of the BIND libresolv.so.2 being used. 144 */ 145 if ((get_h_errno = (int *(*)(void))dlsym(reslib, 146 __H_ERRNO)) != 0) { 147 /* BIND 8.2.2 libresolv.so.2 is MT safe. */ 148 enable_mt = __is_mt_safe; 149 disable_mt = __is_mt_safe; 150 } else { 151 if ((get_h_errno = 152 (int *(*)(void))dlsym(reslib, 153 RES_GET_H_ERRNO)) == 0) { 154 get_h_errno = __fallback_h_errno; 155 } 156 /* 157 * Pre-BIND 8.2.2 was not MT safe. Try to 158 * bind the MT enable/disable functions. 159 */ 160 if ((enable_mt = (int (*)(void))dlsym(reslib, 161 RES_ENABLE_MT)) != 0 && 162 (disable_mt = (int (*)(void))dlsym(reslib, 163 RES_DISABLE_MT)) == 0) { 164 enable_mt = 0; 165 } 166 } 167 } 168 } else { 169 /* Libresolv already loaded */ 170 if ((f_void_ptr = __res_set_no_hosts_fallback) != 0) { 171 set_no_hosts_fallback = f_void_ptr; 172 } 173 if ((f_void_ptr = __res_unset_no_hosts_fallback) != 0) { 174 unset_no_hosts_fallback = f_void_ptr; 175 } 176 if ((override_retry = __res_override_retry) == 0) { 177 set_res_retry = __res_get_res; 178 override_retry = __fallback_override_retry; 179 } 180 if ((get_h_errno = __h_errno) == 0 && 181 (get_h_errno = __res_get_h_errno) == 0) { 182 get_h_errno = __fallback_h_errno; 183 } 184 if (get_h_errno == __h_errno) { 185 enable_mt = __is_mt_safe; 186 disable_mt = __is_mt_safe; 187 } else { 188 if ((enable_mt = __res_enable_mt) != 0 && 189 (disable_mt = __res_disable_mt) == 0) { 190 enable_mt = 0; 191 } 192 } 193 } 194 } 195 196 197 /* 198 * 199 * Integration of BIND 8.1.2 introduced two new Sun private functions, 200 * __res_enable_mt() and __res_disable_mt(), that enabled and disabled 201 * MT mode per-thread. These functions are in the private libresolv.so.2 202 * interface, and intended for use by nss_dns.so.1. 203 * 204 * BIND 8.2.2 removed the need for those two functions. As similar 205 * functionality was provided in BIND further up the stack. However the 206 * functions remain to satisfy any application that directly called upon 207 * them. Only, __res_enable_mt() was modified to return failure. 208 * Indicated by a non-zero return value. So that those unconventional 209 * applications would not then presume that res_send() and friends are 210 * MT-safe, when in fact they are not. 211 * 212 * To prevent nss_dns from locking inappropriately __is_mt_safe() is 213 * called in place of __res_enable_mt() and __res_disable_mt() if BIND 214 * 8.2.2 libresolv.so.2 being used. __is_mt_safe() returns success 215 * indicated by a return code of zero. Signifying that no locking is 216 * necessary. 217 * 218 * MT applications making calls to gethostby*_r() or getipnodeby*() 219 * linked to libresolv.so.1 or linked statically with pre-BIND 8.2.2 220 * libresolv.a, doubtful as we don't ship a static version, would require 221 * locking within the nsswitch back-end. Hence the mechanism can not 222 * simply be removed. 223 * 224 */ 225 static int 226 __is_mt_safe(void) { 227 return (0); 228 } 229 230 231 /* 232 * Return pointer to the global h_errno variable 233 */ 234 static int * 235 __fallback_h_errno(void) { 236 return (&h_errno); 237 } 238 239 240 /* 241 * This function is called when the resolver library doesn't provide its 242 * own function to establish an override retry. If we can get a pointer 243 * to the per-thread _res (i.e., set_res_retry != 0), we set the retries 244 * directly, and return the previous number of retries. Otherwise, there's 245 * nothing to do. 246 */ 247 static int 248 __fallback_override_retry(int retry) { 249 struct __res_state *res; 250 int old_retry = 0; 251 252 if (set_res_retry != 0) { 253 res = set_res_retry(); 254 old_retry = res->retry; 255 res->retry = retry; 256 } 257 return (old_retry); 258 } 259 260 261 static void 262 __fallback_set_no_hosts(void) { 263 } 264 265 266 /* 267 * Common code to enable/disable MT mode, set/unset no-/etc/hosts fallback, 268 * and to set the number of retries. 269 */ 270 void 271 switch_resolver_setup(int *mt_disabled, sigset_t *oldmask, int *old_retry) { 272 273 /* 274 * Try to enable MT mode. If that isn't possible, mask signals, 275 * and mutex_lock. 276 */ 277 *mt_disabled = 1; 278 if (enable_mt == 0 || (*mt_disabled = (*enable_mt)()) != 0) { 279 sigset_t newmask; 280 (void) sigfillset(&newmask); 281 (void) thr_sigsetmask(SIG_SETMASK, &newmask, oldmask); 282 (void) mutex_lock(&one_lane); 283 } 284 285 /* 286 * Disable any fallback to /etc/hosts (or /etc/inet/ipnodes, when 287 * libresolv knows about that file). 288 */ 289 (*set_no_hosts_fallback)(); 290 291 /* 292 * The NS switch wants to handle retries on its own. 293 */ 294 *old_retry = (*override_retry)(1); 295 } 296 297 298 void 299 switch_resolver_reset(int mt_disabled, sigset_t oldmask, int old_retry) { 300 301 if (mt_disabled) { 302 (void) mutex_unlock(&one_lane); 303 (void) thr_sigsetmask(SIG_SETMASK, &oldmask, NULL); 304 } else { 305 (void) (*disable_mt)(); 306 } 307 308 (*unset_no_hosts_fallback)(); 309 310 (void) (*override_retry)(old_retry); 311 } 312