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 #if 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_set_str(&root, rootdir);
  98         varbuf_set_str(&src, pathname);
  99         varbuf_set_str(&result, rootdir);
 100
 101         /* Check whether the path is relative, make it absolute otherwise. */
 102         if (src.buf[0] != '/') {
 103                 struct varbuf abs_src = VARBUF_INIT;
 104
 105                 file_getcwd(&abs_src);
 106                 varbuf_add_char(&abs_src, '/');
 107                 varbuf_add_varbuf(&abs_src, &src);
 108
 109                 varbuf_set_varbuf(&src, &abs_src);
 110                 varbuf_destroy(&abs_src);
 111
 112                 varbuf_trim_varbuf_prefix(&src, &root);
 113         }
 114
 115         /* Remove prefixed slashes. */
 116         varbuf_trim_char_prefix(&src, '/');
 117
 118         while (src.used) {
 119                 struct stat st;
 120                 const char *slash;
 121
 122                 /* Get the first directory component. */
 123                 varbuf_set_varbuf(&prefix, &src);
 124                 slash = strchrnul(prefix.buf, '/');
 125                 varbuf_trunc(&prefix, slash - prefix.buf);
 126
 127                 /* Remove the first directory component from src. */
 128                 varbuf_trim_varbuf_prefix(&src, &prefix);
 129
 130                 /* Remove prefixed slashes. */
 131                 varbuf_trim_char_prefix(&src, '/');
 132
 133                 varbuf_set_varbuf(&slink, &result);
 134                 varbuf_add_char(&slink, '/');
 135                 varbuf_add_varbuf(&slink, &prefix);
 136
 137                 /* Resolve the first directory component. */
 138                 if (strcmp(prefix.buf, ".") == 0) {
 139                         /* Ignore, stay at the same directory. */
 140                 } else if (strcmp(prefix.buf, "..") == 0) {
 141                         /* Go up one directory. */
 142                         slash = strrchr(result.buf, '/');
 143                         if (slash != NULL)
 144                                 varbuf_trunc(&result, slash - result.buf);
 145
 146                         if (root.used && !varbuf_has_prefix(&result, &root))
 147                                 varbuf_set_varbuf(&result, &root);
 148                 } else if (lstat(slink.buf, &st) == 0 && S_ISLNK(st.st_mode)) {
 149                         ssize_t linksize;
 150
 151                         loop++;
 152                         if (loop > 25)
 153                                 ohshit(_("too many levels of symbolic links"));
 154
 155                         /* Resolve the symlink within result. */
 156                         linksize = file_readlink(slink.buf, &dst, st.st_size);
 157                         if (linksize < 0)
 158                                 ohshite(_("cannot read link '%s'"), slink.buf);
 159                         else if ((off_t)linksize != st.st_size)
 160                                 ohshit(_("symbolic link '%s' size has changed from %jd to %zd"),
 161                                        slink.buf, (intmax_t)st.st_size, linksize);
 162
 163                         if (dst.buf[0] == '/') {
 164                                 /* Absolute pathname, reset result back to
 165                                  * root. */
 166                                 varbuf_set_varbuf(&result, &root);
 167
 168                                 if (src.used) {
 169                                         varbuf_add_char(&dst, '/');
 170                                         varbuf_add_varbuf(&dst, &src);
 171                                 }
 172                                 varbuf_set_varbuf(&src, &dst);
 173
 174                                 /* Remove prefixed slashes. */
 175                                 varbuf_trim_char_prefix(&src, '/');
 176                         } else {
 177                                 /* Relative pathname. */
 178                                 if (src.used) {
 179                                         varbuf_add_char(&dst, '/');
 180                                         varbuf_add_varbuf(&dst, &src);
 181                                 }
 182                                 varbuf_set_varbuf(&src, &dst);
 183                         }
 184                 } else {
 185                         /* Otherwise append the prefix. */
 186                         varbuf_add_char(&result, '/');
 187                         varbuf_add_varbuf(&result, &prefix);
 188                 }
 189         }
 190
 191         /* We are done, return the resolved pathname, w/o root. */
 192         varbuf_trim_varbuf_prefix(&result, &root);
 193
 194         varbuf_destroy(&root);
 195         varbuf_destroy(&src);
 196         varbuf_destroy(&dst);
 197         varbuf_destroy(&slink);
 198         varbuf_destroy(&prefix);
 199
 200         return varbuf_detach(&result);
 201 }
 202
 203 static const struct cmdinfo cmdinfos[] = {
 204         { "zero",       'z', 0,  &opt_eol,     NULL,      NULL,         '\0' },
 205         { "instdir",    0,   1,  NULL,         NULL,      set_instdir,  0 },
 206         { "root",       0,   1,  NULL,         NULL,      set_instdir,  0 },
 207         { "version",    0,   0,  NULL,         NULL,      printversion  },
 208         { "help",       '?', 0,  NULL,         NULL,      usage         },
 209         {  NULL,        0                                               }
 210 };
 211
 212 int
 213 main(int argc, const char *const *argv)
 214 {
 215         const char *instdir;
 216         const char *pathname;
 217         char *real_pathname;
 218
 219         dpkg_locales_init(PACKAGE);
 220         dpkg_program_init("dpkg-realpath");
 221         dpkg_options_parse(&argv, cmdinfos, printforhelp);
 222
 223         debug(dbg_general, "root=%s admindir=%s", dpkg_fsys_get_dir(), dpkg_db_get_dir());
 224
 225         pathname = argv[0];
 226         if (pathname == NULL)
 227                 badusage(_("need a pathname argument"));
 228
 229         instdir = dpkg_fsys_get_dir();
 230         if (strlen(instdir) && strncmp(pathname, instdir, strlen(instdir)) == 0)
 231                 badusage(_("link '%s' includes root prefix '%s'"),
 232                          pathname, instdir);
 233
 234         real_pathname = realpath_relative_to(pathname, instdir);
 235         printf("%s%c", real_pathname, opt_eol);
 236         free(real_pathname);
 237
 238         dpkg_program_done();
 239         dpkg_locales_done();
 240
 241         return 0;
 242 }