elf/dl-cache.c

   1 /* Support for reading /etc/ld.so.cache files written by Linux ldconfig.
   2    Copyright (C) 1996-2016 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <assert.h>
  20 #include <unistd.h>
  21 #include <ldsodefs.h>
  22 #include <sys/mman.h>
  23 #include <dl-cache.h>
  24 #include <dl-procinfo.h>
  25 #include <stdint.h>
  26 #include <_itoa.h>
  27
  28 #ifndef _DL_PLATFORMS_COUNT
  29 # define _DL_PLATFORMS_COUNT 0
  30 #endif
  31
  32 /* This is the starting address and the size of the mmap()ed file.  */
  33 static struct cache_file *cache;
  34 static struct cache_file_new *cache_new;
  35 static size_t cachesize;
  36
  37 /* 1 if cache_data + PTR points into the cache.  */
  38 #define _dl_cache_verify_ptr(ptr) (ptr < cache_data_size)
  39
  40 #define SEARCH_CACHE(cache) \
  41 /* We use binary search since the table is sorted in the cache file.          \
  42    The first matching entry in the table is returned.                         \
  43    It is important to use the same algorithm as used while generating         \
  44    the cache file.  */                                                        \
  45 do                                                                            \
  46   {                                                                           \
  47     left = 0;                                                                 \
  48     right = cache->nlibs - 1;                                                 \
  49                                                                               \
  50     while (left <= right)                                                     \
  51       {                                                                       \
  52         __typeof__ (cache->libs[0].key) key;                                  \
  53                                                                               \
  54         middle = (left + right) / 2;                                          \
  55                                                                               \
  56         key = cache->libs[middle].key;                                        \
  57                                                                               \
  58         /* Make sure string table indices are not bogus before using          \
  59            them.  */                                                          \
  60         if (! _dl_cache_verify_ptr (key))                                     \
  61           {                                                                   \
  62             cmpres = 1;                                                       \
  63             break;                                                            \
  64           }                                                                   \
  65                                                                               \
  66         /* Actually compare the entry with the key.  */                       \
  67         cmpres = _dl_cache_libcmp (name, cache_data + key);                   \
  68         if (__glibc_unlikely (cmpres == 0))                                   \
  69           {                                                                   \
  70             /* Found it.  LEFT now marks the last entry for which we          \
  71                know the name is correct.  */                                  \
  72             left = middle;                                                    \
  73                                                                               \
  74             /* There might be entries with this name before the one we        \
  75                found.  So we have to find the beginning.  */                  \
  76             while (middle > 0)                                                \
  77               {                                                               \
  78                 __typeof__ (cache->libs[0].key) key;                          \
  79                                                                               \
  80                 key = cache->libs[middle - 1].key;                            \
  81                 /* Make sure string table indices are not bogus before        \
  82                    using them.  */                                            \
  83                 if (! _dl_cache_verify_ptr (key)                              \
  84                     /* Actually compare the entry.  */                        \
  85                     || _dl_cache_libcmp (name, cache_data + key) != 0)        \
  86                   break;                                                      \
  87                 --middle;                                                     \
  88               }                                                               \
  89                                                                               \
  90             do                                                                \
  91               {                                                               \
  92                 int flags;                                                    \
  93                 __typeof__ (cache->libs[0]) *lib = &cache->libs[middle];      \
  94                                                                               \
  95                 /* Only perform the name test if necessary.  */               \
  96                 if (middle > left                                             \
  97                     /* We haven't seen this string so far.  Test whether the  \
  98                        index is ok and whether the name matches.  Otherwise   \
  99                        we are done.  */                                       \
 100                     && (! _dl_cache_verify_ptr (lib->key)                     \
 101                         || (_dl_cache_libcmp (name, cache_data + lib->key)    \
 102                             != 0)))                                           \
 103                   break;                                                      \
 104                                                                               \
 105                 flags = lib->flags;                                           \
 106                 if (_dl_cache_check_flags (flags)                             \
 107                     && _dl_cache_verify_ptr (lib->value))                     \
 108                   {                                                           \
 109                     if (best == NULL || flags == GLRO(dl_correct_cache_id))   \
 110                       {                                                       \
 111                         HWCAP_CHECK;                                          \
 112                         best = cache_data + lib->value;                       \
 113                                                                               \
 114                         if (flags == GLRO(dl_correct_cache_id))               \
 115                           /* We've found an exact match for the shared        \
 116                              object and no general `ELF' release.  Stop       \
 117                              searching.  */                                   \
 118                           break;                                              \
 119                       }                                                       \
 120                   }                                                           \
 121               }                                                               \
 122             while (++middle <= right);                                        \
 123             break;                                                            \
 124         }                                                                     \
 125                                                                               \
 126         if (cmpres < 0)                                                       \
 127           left = middle + 1;                                                  \
 128         else                                                                  \
 129           right = middle - 1;                                                 \
 130       }                                                                       \
 131   }                                                                           \
 132 while (0)
 133
 134
 135 int
 136 internal_function
 137 _dl_cache_libcmp (const char *p1, const char *p2)
 138 {
 139   while (*p1 != '\0')
 140     {
 141       if (*p1 >= '0' && *p1 <= '9')
 142         {
 143           if (*p2 >= '0' && *p2 <= '9')
 144             {
 145               /* Must compare this numerically.  */
 146               int val1;
 147               int val2;
 148
 149               val1 = *p1++ - '0';
 150               val2 = *p2++ - '0';
 151               while (*p1 >= '0' && *p1 <= '9')
 152                 val1 = val1 * 10 + *p1++ - '0';
 153               while (*p2 >= '0' && *p2 <= '9')
 154                 val2 = val2 * 10 + *p2++ - '0';
 155               if (val1 != val2)
 156                 return val1 - val2;
 157             }
 158           else
 159             return 1;
 160         }
 161       else if (*p2 >= '0' && *p2 <= '9')
 162         return -1;
 163       else if (*p1 != *p2)
 164         return *p1 - *p2;
 165       else
 166         {
 167           ++p1;
 168           ++p2;
 169         }
 170     }
 171   return *p1 - *p2;
 172 }
 173
 174
 175 /* Look up NAME in ld.so.cache and return the file name stored there, or null
 176    if none is found.  The cache is loaded if it was not already.  If loading
 177    the cache previously failed there will be no more attempts to load it.
 178    The caller is responsible for freeing the returned string.  The ld.so.cache
 179    may be unmapped at any time by a completing recursive dlopen and
 180    this function must take care that it does not return references to
 181    any data in the mapping.  */
 182 char *
 183 internal_function
 184 _dl_load_cache_lookup (const char *name)
 185 {
 186   int left, right, middle;
 187   int cmpres;
 188   const char *cache_data;
 189   uint32_t cache_data_size;
 190   const char *best;
 191
 192   /* Print a message if the loading of libs is traced.  */
 193   if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_LIBS))
 194     _dl_debug_printf (" search cache=%s\n", LD_SO_CACHE);
 195
 196   if (cache == NULL)
 197     {
 198       /* Read the contents of the file.  */
 199       void *file = _dl_sysdep_read_whole_file (LD_SO_CACHE, &cachesize,
 200                                                PROT_READ);
 201
 202       /* We can handle three different cache file formats here:
 203          - the old libc5/glibc2.0/2.1 format
 204          - the old format with the new format in it
 205          - only the new format
 206          The following checks if the cache contains any of these formats.  */
 207       if (file != MAP_FAILED && cachesize > sizeof *cache
 208           && memcmp (file, CACHEMAGIC, sizeof CACHEMAGIC - 1) == 0)
 209         {
 210           size_t offset;
 211           /* Looks ok.  */
 212           cache = file;
 213
 214           /* Check for new version.  */
 215           offset = ALIGN_CACHE (sizeof (struct cache_file)
 216                                 + cache->nlibs * sizeof (struct file_entry));
 217
 218           cache_new = (struct cache_file_new *) ((void *) cache + offset);
 219           if (cachesize < (offset + sizeof (struct cache_file_new))
 220               || memcmp (cache_new->magic, CACHEMAGIC_VERSION_NEW,
 221                          sizeof CACHEMAGIC_VERSION_NEW - 1) != 0)
 222             cache_new = (void *) -1;
 223         }
 224       else if (file != MAP_FAILED && cachesize > sizeof *cache_new
 225                && memcmp (file, CACHEMAGIC_VERSION_NEW,
 226                           sizeof CACHEMAGIC_VERSION_NEW - 1) == 0)
 227         {
 228           cache_new = file;
 229           cache = file;
 230         }
 231       else
 232         {
 233           if (file != MAP_FAILED)
 234             __munmap (file, cachesize);
 235           cache = (void *) -1;
 236         }
 237
 238       assert (cache != NULL);
 239     }
 240
 241   if (cache == (void *) -1)
 242     /* Previously looked for the cache file and didn't find it.  */
 243     return NULL;
 244
 245   best = NULL;
 246
 247   if (cache_new != (void *) -1)
 248     {
 249       uint64_t platform;
 250
 251       /* This is where the strings start.  */
 252       cache_data = (const char *) cache_new;
 253
 254       /* Now we can compute how large the string table is.  */
 255       cache_data_size = (const char *) cache + cachesize - cache_data;
 256
 257       platform = _dl_string_platform (GLRO(dl_platform));
 258       if (platform != (uint64_t) -1)
 259         platform = 1ULL << platform;
 260
 261 #define _DL_HWCAP_TLS_MASK (1LL << 63)
 262       uint64_t hwcap_exclude = ~((GLRO(dl_hwcap) & GLRO(dl_hwcap_mask))
 263                                  | _DL_HWCAP_PLATFORM | _DL_HWCAP_TLS_MASK);
 264
 265       /* Only accept hwcap if it's for the right platform.  */
 266 #define HWCAP_CHECK \
 267       if (lib->hwcap & hwcap_exclude)                                         \
 268         continue;                                                             \
 269       if (GLRO(dl_osversion) && lib->osversion > GLRO(dl_osversion))          \
 270         continue;                                                             \
 271       if (_DL_PLATFORMS_COUNT                                                 \
 272           && (lib->hwcap & _DL_HWCAP_PLATFORM) != 0                           \
 273           && (lib->hwcap & _DL_HWCAP_PLATFORM) != platform)                   \
 274         continue
 275       SEARCH_CACHE (cache_new);
 276     }
 277   else
 278     {
 279       /* This is where the strings start.  */
 280       cache_data = (const char *) &cache->libs[cache->nlibs];
 281
 282       /* Now we can compute how large the string table is.  */
 283       cache_data_size = (const char *) cache + cachesize - cache_data;
 284
 285 #undef HWCAP_CHECK
 286 #define HWCAP_CHECK do {} while (0)
 287       SEARCH_CACHE (cache);
 288     }
 289
 290   /* Print our result if wanted.  */
 291   if (__builtin_expect (GLRO(dl_debug_mask) & DL_DEBUG_LIBS, 0)
 292       && best != NULL)
 293     _dl_debug_printf ("  trying file=%s\n", best);
 294
 295   if (best == NULL)
 296     return NULL;
 297
 298   /* The double copy is *required* since malloc may be interposed
 299      and call dlopen itself whose completion would unmap the data
 300      we are accessing. Therefore we must make the copy of the
 301      mapping data without using malloc.  */
 302   char *temp;
 303   temp = alloca (strlen (best) + 1);
 304   strcpy (temp, best);
 305   return strdup (temp);
 306 }
 307
 308 #ifndef MAP_COPY
 309 /* If the system does not support MAP_COPY we cannot leave the file open
 310    all the time since this would create problems when the file is replaced.
 311    Therefore we provide this function to close the file and open it again
 312    once needed.  */
 313 void
 314 _dl_unload_cache (void)
 315 {
 316   if (cache != NULL && cache != (struct cache_file *) -1)
 317     {
 318       __munmap (cache, cachesize);
 319       cache = NULL;
 320     }
 321 }
 322 #endif