src/realpath/main.c

   1 /*
   2  * dpkg-realpath - print the resolved pathname with DPKG_ROOT support
   3  *
   4  * Copyright © 2020 Helmut Grohne <helmut@subdivi.de>
   5  * Copyright © 2020-2024 Guillem Jover <guillem@debian.org>
   6  *
   7  * This is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License as published by
   9  * the Free Software Foundation; either version 2 of the License, or
  10  * (at your option) any later version.
  11  *
  12  * This is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15  * GNU General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU General Public License
  18  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  19  */
  20
  21 #include <config.h>
  22 #include <compat.h>
  23
  24 #include <sys/types.h>
  25 #include <sys/stat.h>
  26
  27 #include <errno.h>
  28 #ifdef HAVE_LOCALE_H
  29 #include <locale.h>
  30 #endif
  31 #include <string.h>
  32 #include <unistd.h>
  33 #include <stdint.h>
  34 #include <stdlib.h>
  35 #include <stdio.h>
  36
  37 #include <dpkg/i18n.h>
  38 #include <dpkg/dpkg.h>
  39 #include <dpkg/dpkg-db.h>
  40 #include <dpkg/debug.h>
  41 #include <dpkg/string.h>
  42 #include <dpkg/db-fsys.h>
  43 #include <dpkg/options.h>
  44
  45 static const char printforhelp[] = N_(
  46 "Use --help for help about this utility.");
  47
  48 static void DPKG_ATTR_NORET
  49 printversion(const struct cmdinfo *cip, const char *value)
  50 {
  51         printf(_("Debian %s version %s.\n"), dpkg_get_progname(),
  52                PACKAGE_RELEASE);
  53
  54         printf(_(
  55 "This is free software; see the GNU General Public License version 2 or\n"
  56 "later for copying conditions. There is NO warranty.\n"));
  57
  58         m_output(stdout, _("<standard output>"));
  59
  60         exit(0);
  61 }
  62
  63 static void DPKG_ATTR_NORET
  64 usage(const struct cmdinfo *cip, const char *value)
  65 {
  66         printf(_(
  67 "Usage: %s [<option>...] <pathname>\n"
  68 "\n"), dpkg_get_progname());
  69
  70         printf(_(
  71 "Options:\n"
  72 "  -z, --zero                   end output line with NUL, not newline.\n"
  73 "      --instdir <directory>    set the root directory.\n"
  74 "      --root <directory>       set the root directory.\n"
  75 "      --version                show the version.\n"
  76 "      --help                   show this help message.\n"
  77 "\n"));
  78
  79         m_output(stdout, _("<standard output>"));
  80
  81         exit(0);
  82 }
  83
  84 static int opt_eol = '\n';
  85
  86 static char *
  87 realpath_relative_to(const char *pathname, const char *rootdir)
  88 {
  89         struct varbuf root = VARBUF_INIT;
  90         struct varbuf src = VARBUF_INIT;
  91         struct varbuf dst = VARBUF_INIT;
  92         struct varbuf slink = VARBUF_INIT;
  93         struct varbuf result = VARBUF_INIT;
  94         struct varbuf prefix = VARBUF_INIT;
  95         int loop = 0;
  96
  97         varbuf_init(&root, 32);
  98         varbuf_init(&src, 32);
  99         varbuf_init(&dst, 32);
 100         varbuf_init(&result, 32);
 101
 102         varbuf_set_str(&root, rootdir);
 103         varbuf_set_str(&src, pathname);
 104         varbuf_set_str(&result, rootdir);
 105
 106         /* Check whether the path is relative, make it absolute otherwise. */
 107         if (src.buf[0] != '/') {
 108                 struct varbuf abs_src = VARBUF_INIT;
 109
 110                 file_getcwd(&abs_src);
 111                 varbuf_add_char(&abs_src, '/');
 112                 varbuf_add_varbuf(&abs_src, &src);
 113
 114                 varbuf_set_varbuf(&src, &abs_src);
 115                 varbuf_destroy(&abs_src);
 116
 117                 varbuf_trim_varbuf_prefix(&src, &root);
 118         }
 119
 120         /* Remove prefixed slashes. */
 121         varbuf_trim_char_prefix(&src, '/');
 122
 123         while (src.used) {
 124                 struct stat st;
 125                 const char *slash;
 126
 127                 /* Get the first directory component. */
 128                 varbuf_set_varbuf(&prefix, &src);
 129                 slash = strchrnul(prefix.buf, '/');
 130                 varbuf_trunc(&prefix, slash - prefix.buf);
 131
 132                 /* Remove the first directory component from src. */
 133                 varbuf_trim_varbuf_prefix(&src, &prefix);
 134
 135                 /* Remove prefixed slashes. */
 136                 varbuf_trim_char_prefix(&src, '/');
 137
 138                 varbuf_set_varbuf(&slink, &result);
 139                 varbuf_add_char(&slink, '/');
 140                 varbuf_add_varbuf(&slink, &prefix);
 141
 142                 /* Resolve the first directory component. */
 143                 if (strcmp(prefix.buf, ".") == 0) {
 144                         /* Ignore, stay at the same directory. */
 145                 } else if (strcmp(prefix.buf, "..") == 0) {
 146                         /* Go up one directory. */
 147                         slash = strrchr(result.buf, '/');
 148                         if (slash != NULL)
 149                                 varbuf_trunc(&result, slash - result.buf);
 150
 151                         if (root.used && !varbuf_has_prefix(&result, &root))
 152                                 varbuf_set_varbuf(&result, &root);
 153                 } else if (lstat(slink.buf, &st) == 0 && S_ISLNK(st.st_mode)) {
 154                         ssize_t linksize;
 155
 156                         loop++;
 157                         if (loop > 25)
 158                                 ohshit(_("too many levels of symbolic links"));
 159
 160                         /* Resolve the symlink within result. */
 161                         linksize = file_readlink(slink.buf, &dst, st.st_size);
 162                         if (linksize < 0)
 163                                 ohshite(_("cannot read link '%s'"), slink.buf);
 164                         else if ((off_t)linksize != st.st_size)
 165                                 ohshit(_("symbolic link '%s' size has changed from %jd to %zd"),
 166                                        slink.buf, (intmax_t)st.st_size, linksize);
 167
 168                         if (dst.buf[0] == '/') {
 169                                 /* Absolute pathname, reset result back to
 170                                  * root. */
 171                                 varbuf_set_varbuf(&result, &root);
 172
 173                                 if (src.used) {
 174                                         varbuf_add_char(&dst, '/');
 175                                         varbuf_add_varbuf(&dst, &src);
 176                                 }
 177                                 varbuf_set_varbuf(&src, &dst);
 178
 179                                 /* Remove prefixed slashes. */
 180                                 varbuf_trim_char_prefix(&src, '/');
 181                         } else {
 182                                 /* Relative pathname. */
 183                                 if (src.used) {
 184                                         varbuf_add_char(&dst, '/');
 185                                         varbuf_add_varbuf(&dst, &src);
 186                                 }
 187                                 varbuf_set_varbuf(&src, &dst);
 188                         }
 189                 } else {
 190                         /* Otherwise append the prefix. */
 191                         varbuf_add_char(&result, '/');
 192                         varbuf_add_varbuf(&result, &prefix);
 193                 }
 194         }
 195
 196         /* We are done, return the resolved pathname, w/o root. */
 197         varbuf_trim_varbuf_prefix(&result, &root);
 198
 199         varbuf_destroy(&root);
 200         varbuf_destroy(&src);
 201         varbuf_destroy(&dst);
 202         varbuf_destroy(&slink);
 203         varbuf_destroy(&prefix);
 204
 205         return varbuf_detach(&result);
 206 }
 207
 208 static const struct cmdinfo cmdinfos[] = {
 209         { "zero",       'z', 0,  &opt_eol,     NULL,      NULL,         '\0' },
 210         { "instdir",    0,   1,  NULL,         NULL,      set_instdir,  0 },
 211         { "root",       0,   1,  NULL,         NULL,      set_instdir,  0 },
 212         { "version",    0,   0,  NULL,         NULL,      printversion  },
 213         { "help",       '?', 0,  NULL,         NULL,      usage         },
 214         {  NULL,        0                                               }
 215 };
 216
 217 int
 218 main(int argc, const char *const *argv)
 219 {
 220         const char *instdir;
 221         const char *pathname;
 222         char *real_pathname;
 223
 224         dpkg_locales_init(PACKAGE);
 225         dpkg_program_init("dpkg-realpath");
 226         dpkg_options_parse(&argv, cmdinfos, printforhelp);
 227
 228         debug(dbg_general, "root=%s admindir=%s", dpkg_fsys_get_dir(), dpkg_db_get_dir());
 229
 230         pathname = argv[0];
 231         if (str_is_unset(pathname))
 232                 badusage(_("need a pathname argument"));
 233
 234         instdir = dpkg_fsys_get_dir();
 235         if (strlen(instdir) && strncmp(pathname, instdir, strlen(instdir)) == 0)
 236                 badusage(_("link '%s' includes root prefix '%s'"),
 237                          pathname, instdir);
 238
 239         real_pathname = realpath_relative_to(pathname, instdir);
 240         printf("%s%c", real_pathname, opt_eol);
 241         free(real_pathname);
 242
 243         dpkg_program_done();
 244         dpkg_locales_done();
 245
 246         return 0;
 247 }