ipc.c

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2
   3 #include <sys/wait.h>
   4 #include <stdio.h>
   5 #include <inttypes.h>
   6 #include <stdlib.h>
   7 #include <unistd.h>
   8 #include <errno.h>
   9 #include <sys/types.h>
  10 #include <sys/ipc.h>
  11 #include <sys/sem.h>
  12 #include <string.h>
  13 #include <assert.h>
  14 #include <sys/stat.h>
  15 #include <stddef.h>
  16 #include <limits.h>
  17 #include <sys/param.h>
  18 #include <stdbool.h>
  19
  20 #include "gcc-compat.h"
  21 #include "str.h"
  22 #include "log.h"
  23 #include "gcc-compat.h"
  24 #include "err.h"
  25 #include "ipc.h"
  26
  27 #if (defined(__GNUC__) && defined(__i386__))
  28 #define get16bits(d) (*((const uint16_t *) (d)))
  29 #else
  30 #define get16bits(d) ((((uint32_t)(((const uint8_t *)(d))[1])) << 8)\
  31                 +(uint32_t)(((const uint8_t *)(d))[0]) )
  32 #endif
  33
  34 /*
  35  * SuperFastHash, by Paul Hsieh.
  36  * http://www.azillionmonkeys.com/qed/hash.html
  37  */
  38 static uint32_t super_fast_hash(const uint8_t *data, uint32_t len, uint32_t hash)
  39 {
  40         uint32_t tmp;
  41         int rem = len & 3;
  42
  43         len >>= 2;
  44
  45         for (;len > 0; len--) {
  46                 hash  += get16bits (data);
  47                 tmp    = (get16bits (data+2) << 11) ^ hash;
  48                 hash   = (hash << 16) ^ tmp;
  49                 data  += 2*sizeof (uint16_t);
  50                 hash  += hash >> 11;
  51         }
  52
  53         /* Handle end cases */
  54         switch (rem) {
  55         case 3:
  56                 hash += get16bits (data);
  57                 hash ^= hash << 16;
  58                 hash ^= data[sizeof (uint16_t)] << 18;
  59                 hash += hash >> 11;
  60                 break;
  61         case 2:
  62                 hash += get16bits (data);
  63                 hash ^= hash << 11;
  64                 hash += hash >> 17;
  65                 break;
  66         case 1:
  67                 hash += *data;
  68                 hash ^= hash << 10;
  69                 hash += hash >> 1;
  70         }
  71         /* Force "avalanching" of final 127 bits */
  72         hash ^= hash << 3;
  73         hash += hash >> 5;
  74         hash ^= hash << 4;
  75         hash += hash >> 17;
  76         hash ^= hash << 25;
  77         hash += hash >> 6;
  78         return hash;
  79 }
  80
  81 /*
  82  * Return the canonical absolute name of a given file name.
  83  *
  84  * Slightly modified version of glibc's realpath, Copyright (C)
  85  * 1996-2002,2004,2005,2006,2008 Free Software Foundation, Inc.
  86  *
  87  * A canonical name does not contain any `.', `..' components nor any repeated
  88  * path separators ('/') or symlinks. All path components must exist. The
  89  * result is malloc'd and must be freed by the caller.
  90  */
  91 static int dss_realpath(const char *name, char **resolved_path)
  92 {
  93         char *rpath = NULL, *dest, *extra_buf = NULL;
  94         const char *start, *end, *rpath_limit;
  95         long int path_max;
  96         int ret, num_links = 0;
  97
  98         if (name[0] == '\0') {
  99                 /*
 100                  * As per Single Unix Specification V2 we must return an error
 101                  * if the name argument points to an empty string.
 102                  */
 103                 ret = -ERRNO_TO_DSS_ERROR(ENOENT);
 104                 goto error;
 105         }
 106 #ifdef PATH_MAX
 107         path_max = PATH_MAX;
 108 #else
 109         /*
 110          * From realpath(3): Asking pathconf(3) does not really help, since on
 111          * the one hand POSIX warns that the result of pathconf(3) may be
 112          * huge and unsuitable for mallocing memory. And on the other hand
 113          * pathconf(3) may return -1 to signify that PATH_MAX is not bounded.
 114          */
 115         path_max = pathconf(name, _PC_PATH_MAX);
 116         if (path_max <= 0 || path_max >= 4096)
 117                 path_max = 4096;
 118 #endif
 119         rpath = dss_malloc(path_max);
 120         rpath_limit = rpath + path_max;
 121
 122         if (name[0] != '/') {
 123                 if (!getcwd(rpath, path_max)) {
 124                         ret = -ERRNO_TO_DSS_ERROR(errno);
 125                         goto error;
 126                 }
 127                 dest = memchr(rpath, '\0', path_max);
 128         } else {
 129                 rpath[0] = '/';
 130                 dest = rpath + 1;
 131         }
 132
 133         for (start = end = name; *start; start = end) {
 134                 struct stat st;
 135                 int n;
 136
 137                 /* Skip sequence of multiple path-separators.  */
 138                 while (*start == '/')
 139                         ++start;
 140
 141                 /* Find end of path component.  */
 142                 for (end = start; *end && *end != '/'; ++end)
 143                         /* Nothing.  */ ;
 144
 145                 if (end - start == 0)
 146                         break;
 147                 else if (end - start == 1 && start[0] == '.')
 148                         /* nothing */ ;
 149                 else if (end - start == 2 && start[0] == '.' && start[1] == '.') {
 150                         /* Back up to previous component, ignore if at root already.  */
 151                         if (dest > rpath + 1)
 152                                 while ((--dest)[-1] != '/') ;
 153                 } else {
 154                         size_t new_size;
 155
 156                         if (dest[-1] != '/')
 157                                 *dest++ = '/';
 158
 159                         if (dest + (end - start) >= rpath_limit) {
 160                                 ptrdiff_t dest_offset = dest - rpath;
 161
 162                                 new_size = rpath_limit - rpath;
 163                                 if (end - start + 1 > path_max)
 164                                         new_size += end - start + 1;
 165                                 else
 166                                         new_size += path_max;
 167                                 rpath = dss_realloc(rpath, new_size);
 168                                 rpath_limit = rpath + new_size;
 169                                 dest = rpath + dest_offset;
 170                         }
 171
 172                         memcpy(dest, start, end - start);
 173                         dest += end - start;
 174                         *dest = '\0';
 175
 176                         if (stat(rpath, &st) < 0) {
 177                                 ret = -ERRNO_TO_DSS_ERROR(errno);
 178                                 goto error;
 179                         }
 180
 181                         if (S_ISLNK(st.st_mode)) {
 182                                 char *buf = alloca(path_max);
 183                                 size_t len;
 184
 185                                 if (++num_links > MAXSYMLINKS) {
 186                                         ret = -ERRNO_TO_DSS_ERROR(ELOOP);
 187                                         goto error;
 188                                 }
 189
 190                                 n = readlink(rpath, buf, path_max - 1);
 191                                 if (n < 0) {
 192                                         ret = -ERRNO_TO_DSS_ERROR(errno);
 193                                         goto error;
 194                                 }
 195                                 buf[n] = '\0';
 196
 197                                 if (!extra_buf)
 198                                         extra_buf = alloca(path_max);
 199
 200                                 len = strlen(end);
 201                                 if ((long int) (n + len) >= path_max) {
 202                                         ret = -ERRNO_TO_DSS_ERROR(ENAMETOOLONG);
 203                                         goto error;
 204                                 }
 205
 206                                 /* Careful here, end may be a pointer into extra_buf... */
 207                                 memmove(&extra_buf[n], end, len + 1);
 208                                 end = memcpy(extra_buf, buf, n);
 209
 210                                 if (buf[0] == '/') /* It's an absolute symlink */
 211                                         dest = rpath + 1;
 212                                 else /* Back up to previous component, ignore if at root already: */
 213                                         if (dest > rpath + 1)
 214                                                 while ((--dest)[-1] != '/')
 215                                                         ; /* nothing */
 216                         } else if (!S_ISDIR(st.st_mode) && *end != '\0') {
 217                                 ret = -ERRNO_TO_DSS_ERROR(ENOTDIR);
 218                                 goto error;
 219                         }
 220                 }
 221         }
 222         if (dest > rpath + 1 && dest[-1] == '/')
 223                 --dest;
 224         *dest = '\0';
 225         *resolved_path = rpath;
 226         return 1;
 227 error:
 228         free(rpath);
 229         *resolved_path = NULL;
 230         return ret;
 231 }
 232
 233 static int get_key_or_die(const char *config_file)
 234 {
 235         int ret;
 236         struct stat statbuf;
 237         char *rpath;
 238
 239         assert(config_file);
 240         if (stat(config_file, &statbuf) == 0) {
 241                 ret = dss_realpath(config_file, &rpath);
 242                 if (ret < 0) {
 243                         DSS_EMERG_LOG(("could not resolve path %s: %s\n", config_file,
 244                                 dss_strerror(-ret)));
 245                         exit(EXIT_FAILURE);
 246                 }
 247                 DSS_DEBUG_LOG(("resolved path: %s\n", rpath));
 248         } else
 249                 /*
 250                  * This happens if the user did not specify a config file, and
 251                  * the default config file does not exist.  Another (unlikely)
 252                  * possibility is that the config file was removed between
 253                  * startup and this call. We don't care about these corner
 254                  * cases too much and just use the unresolved path in this
 255                  * case.
 256                  */
 257                 rpath = dss_strdup(config_file);
 258         ret = super_fast_hash((uint8_t *)rpath, strlen(rpath), 0) >> 1;
 259         free(rpath);
 260         return ret;
 261 }
 262
 263 static int mutex_get(key_t key, int flags)
 264 {
 265         int ret;
 266
 267         DSS_DEBUG_LOG(("getting semaphore 0x%lx\n", (long)key));
 268         ret = semget(key, 2, flags);
 269         if (ret < 0)
 270                 return -ERRNO_TO_DSS_ERROR(errno);
 271         return ret;
 272 }
 273
 274 static int do_semop(int id, struct sembuf *sops, int num)
 275 {
 276         int ret;
 277
 278         DSS_DEBUG_LOG(("calling semop\n"));
 279         do {
 280                 ret = semop(id, sops, num);
 281                 if (ret >= 0)
 282                         return 1;
 283         } while (errno == EINTR);
 284         return -ERRNO_TO_DSS_ERROR(errno);
 285 }
 286
 287 static bool mutex_is_locked(int id)
 288 {
 289         struct sembuf sops;
 290         int ret;
 291
 292         DSS_DEBUG_LOG(("trying to lock\n"));
 293
 294         sops.sem_num = 0;
 295         sops.sem_op = 0;
 296         sops.sem_flg = SEM_UNDO | IPC_NOWAIT;
 297
 298         ret = do_semop(id, &sops, 1);
 299         if (ret < 0)
 300                 return true;
 301         return false;
 302 }
 303
 304 int lock_dss(char *config_file)
 305 {
 306         int ret, id;
 307         struct sembuf sops[4];
 308         key_t key = get_key_or_die(config_file);
 309
 310         ret = mutex_get(key, IPC_CREAT | 0600);
 311         if (ret < 0)
 312                 return ret;
 313         id = ret;
 314
 315         sops[0].sem_num = 0;
 316         sops[0].sem_op = 0;
 317         sops[0].sem_flg = SEM_UNDO | IPC_NOWAIT;
 318
 319         sops[1].sem_num = 0;
 320         sops[1].sem_op = 1;
 321         sops[1].sem_flg = SEM_UNDO | IPC_NOWAIT;
 322
 323         sops[2].sem_num = 1;
 324         sops[2].sem_op = 0;
 325         sops[2].sem_flg = SEM_UNDO | IPC_NOWAIT;
 326
 327         sops[3].sem_num = 1;
 328         sops[3].sem_op = 1;
 329         sops[3].sem_flg = SEM_UNDO | IPC_NOWAIT;
 330
 331         return do_semop(id, sops, 4);
 332 }
 333
 334 int get_dss_pid(char *config_file, pid_t *pid)
 335 {
 336         int ret, semid;
 337         key_t key = get_key_or_die(config_file);
 338
 339         if (pid)
 340                 *pid = 0;
 341         ret = mutex_get(key, 0);
 342         if (ret < 0)
 343                 return ret == -ERRNO_TO_DSS_ERROR(ENOENT)? -E_NOT_RUNNING : ret;
 344         semid = ret;
 345         ret = semctl(semid, 1, GETPID);
 346         if (ret < 0)
 347                 return -E_NOT_RUNNING;
 348         if (pid)
 349                 *pid = ret;
 350         return mutex_is_locked(semid)? 1 : -E_NOT_RUNNING;
 351 }