support/shell-container.c

   1 /* Minimal /bin/sh for in-container use.
   2    Copyright (C) 2018-2021 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    <https://www.gnu.org/licenses/>.  */
  18
  19 #define _FILE_OFFSET_BITS 64
  20
  21 #include <stdio.h>
  22 #include <stdlib.h>
  23 #include <string.h>
  24 #include <sched.h>
  25 #include <sys/syscall.h>
  26 #include <unistd.h>
  27 #include <sys/types.h>
  28 #include <dirent.h>
  29 #include <string.h>
  30 #include <sys/stat.h>
  31 #include <sys/fcntl.h>
  32 #include <sys/file.h>
  33 #include <sys/wait.h>
  34 #include <stdarg.h>
  35 #include <sys/sysmacros.h>
  36 #include <ctype.h>
  37 #include <utime.h>
  38 #include <errno.h>
  39 #include <error.h>
  40
  41 #include <support/support.h>
  42
  43 /* Design considerations
  44
  45  General rule: optimize for developer time, not run time.
  46
  47  Specifically:
  48
  49  * Don't worry about slow algorithms
  50  * Don't worry about free'ing memory
  51  * Don't implement anything the testsuite doesn't need.
  52  * Line and argument counts are limited, see below.
  53
  54 */
  55
  56 #define MAX_ARG_COUNT 100
  57 #define MAX_LINE_LENGTH 1000
  58
  59 /* Debugging is enabled via --debug, which must be the first argument.  */
  60 static int debug_mode = 0;
  61 #define dprintf if (debug_mode) fprintf
  62
  63 /* Emulate the "/bin/true" command.  Arguments are ignored.  */
  64 static int
  65 true_func (char **argv)
  66 {
  67   return 0;
  68 }
  69
  70 /* Emulate the "/bin/echo" command.  Options are ignored, arguments
  71    are printed to stdout.  */
  72 static int
  73 echo_func (char **argv)
  74 {
  75   int i;
  76
  77   for (i = 0; argv[i]; i++)
  78     {
  79       if (i > 0)
  80         putchar (' ');
  81       fputs (argv[i], stdout);
  82     }
  83   putchar ('\n');
  84
  85   return 0;
  86 }
  87
  88 /* Emulate the "/bin/cp" command.  Options are ignored.  Only copies
  89    one source file to one destination file.  Directory destinations
  90    are not supported.  */
  91 static int
  92 copy_func (char **argv)
  93 {
  94   char *sname = argv[0];
  95   char *dname = argv[1];
  96   int sfd = -1, dfd = -1;
  97   struct stat st;
  98   int ret = 1;
  99
 100   sfd = open (sname, O_RDONLY);
 101   if (sfd < 0)
 102     {
 103       fprintf (stderr, "cp: unable to open %s for reading: %s\n",
 104                sname, strerror (errno));
 105       return 1;
 106     }
 107
 108   if (fstat (sfd, &st) < 0)
 109     {
 110       fprintf (stderr, "cp: unable to fstat %s: %s\n",
 111                sname, strerror (errno));
 112       goto out;
 113     }
 114
 115   dfd = open (dname, O_WRONLY | O_TRUNC | O_CREAT, 0600);
 116   if (dfd < 0)
 117     {
 118       fprintf (stderr, "cp: unable to open %s for writing: %s\n",
 119                dname, strerror (errno));
 120       goto out;
 121     }
 122
 123   if (support_copy_file_range (sfd, 0, dfd, 0, st.st_size, 0) != st.st_size)
 124     {
 125       fprintf (stderr, "cp: cannot copy file %s to %s: %s\n",
 126                sname, dname, strerror (errno));
 127       goto out;
 128     }
 129
 130   ret = 0;
 131   chmod (dname, st.st_mode & 0777);
 132
 133 out:
 134   if (sfd >= 0)
 135     close (sfd);
 136   if (dfd >= 0)
 137     close (dfd);
 138
 139   return ret;
 140
 141 }
 142
 143 /* Emulate the 'exit' builtin.  The exit value is optional.  */
 144 static int
 145 exit_func (char **argv)
 146 {
 147   int exit_val = 0;
 148
 149   if (argv[0] != 0)
 150     exit_val = atoi (argv[0]) & 0xff;
 151   exit (exit_val);
 152   return 0;
 153 }
 154
 155 /* Emulate the "/bin/kill" command.  Options are ignored.  */
 156 static int
 157 kill_func (char **argv)
 158 {
 159   int signum = SIGTERM;
 160   int i;
 161
 162   for (i = 0; argv[i]; i++)
 163     {
 164       pid_t pid;
 165       if (strcmp (argv[i], "$$") == 0)
 166         pid = getpid ();
 167       else
 168         pid = atoi (argv[i]);
 169       kill (pid, signum);
 170     }
 171   return 0;
 172 }
 173
 174 /* This is a list of all the built-in commands we understand.  */
 175 static struct {
 176   const char *name;
 177   int (*func) (char **argv);
 178 } builtin_funcs[] = {
 179   { "true", true_func },
 180   { "echo", echo_func },
 181   { "cp", copy_func },
 182   { "exit", exit_func },
 183   { "kill", kill_func },
 184   { NULL, NULL }
 185 };
 186
 187 /* Run one tokenized command.  argv[0] is the command.  argv is
 188    NULL-terminated.  */
 189 static void
 190 run_command_array (char **argv)
 191 {
 192   int i, j;
 193   pid_t pid;
 194   int status;
 195   int (*builtin_func) (char **args);
 196
 197   if (argv[0] == NULL)
 198     return;
 199
 200   builtin_func = NULL;
 201
 202   int new_stdin = 0;
 203   int new_stdout = 1;
 204   int new_stderr = 2;
 205
 206   dprintf (stderr, "run_command_array starting\n");
 207   for (i = 0; argv[i]; i++)
 208     dprintf (stderr, "   argv [%d] `%s'\n", i, argv[i]);
 209
 210   for (j = i = 0; argv[i]; i++)
 211     {
 212       if (strcmp (argv[i], "<") == 0 && argv[i + 1])
 213         {
 214           new_stdin = open (argv[i + 1], O_WRONLY|O_CREAT|O_TRUNC, 0777);
 215           ++i;
 216           continue;
 217         }
 218       if (strcmp (argv[i], ">") == 0 && argv[i + 1])
 219         {
 220           new_stdout = open (argv[i + 1], O_WRONLY|O_CREAT|O_TRUNC, 0777);
 221           ++i;
 222           continue;
 223         }
 224       if (strcmp (argv[i], ">>") == 0 && argv[i + 1])
 225         {
 226           new_stdout = open (argv[i + 1], O_WRONLY|O_CREAT|O_APPEND, 0777);
 227           ++i;
 228           continue;
 229         }
 230       if (strcmp (argv[i], "2>") == 0 && argv[i + 1])
 231         {
 232           new_stderr = open (argv[i + 1], O_WRONLY|O_CREAT|O_TRUNC, 0777);
 233           ++i;
 234           continue;
 235         }
 236       argv[j++] = argv[i];
 237     }
 238   argv[j] = NULL;
 239
 240
 241   for (i = 0; builtin_funcs[i].name != NULL; i++)
 242     if (strcmp (argv[0], builtin_funcs[i].name) == 0)
 243        builtin_func = builtin_funcs[i].func;
 244
 245   dprintf (stderr, "builtin %p argv0 `%s'\n", builtin_func, argv[0]);
 246
 247   pid = fork ();
 248   if (pid < 0)
 249     {
 250       fprintf (stderr, "sh: fork failed\n");
 251       exit (1);
 252     }
 253
 254   if (pid == 0)
 255     {
 256       if (new_stdin != 0)
 257         {
 258           dup2 (new_stdin, 0);
 259           close (new_stdin);
 260         }
 261       if (new_stdout != 1)
 262         {
 263           dup2 (new_stdout, 1);
 264           close (new_stdout);
 265         }
 266       if (new_stderr != 2)
 267         {
 268           dup2 (new_stderr, 2);
 269           close (new_stderr);
 270         }
 271
 272       if (builtin_func != NULL)
 273         exit (builtin_func (argv + 1));
 274
 275       execvp (argv[0], argv);
 276
 277       fprintf (stderr, "sh: execing %s failed: %s",
 278                argv[0], strerror (errno));
 279       exit (127);
 280     }
 281
 282   waitpid (pid, &status, 0);
 283
 284   dprintf (stderr, "exiting run_command_array\n");
 285
 286   if (WIFEXITED (status))
 287     {
 288       int rv = WEXITSTATUS (status);
 289       if (rv)
 290         exit (rv);
 291     }
 292   else if (WIFSIGNALED (status))
 293     {
 294       int sig = WTERMSIG (status);
 295       raise (sig);
 296     }
 297   else
 298     exit (1);
 299 }
 300
 301 /* Run one command-as-a-string, by tokenizing it.  Limited to
 302    MAX_ARG_COUNT arguments.  Simple substitution is done of $1 to $9
 303    (as whole separate tokens) from iargs[].  Quoted strings work if
 304    the quotes wrap whole tokens; i.e. "foo bar" but not foo" bar".  */
 305 static void
 306 run_command_string (const char *cmdline, const char **iargs)
 307 {
 308   char *args[MAX_ARG_COUNT+1];
 309   int ap = 0;
 310   const char *start, *end;
 311   int nargs;
 312
 313   for (nargs = 0; iargs[nargs] != NULL; ++nargs)
 314     ;
 315
 316   dprintf (stderr, "run_command_string starting: '%s'\n", cmdline);
 317
 318   while (ap < MAX_ARG_COUNT)
 319     {
 320       /* If the argument is quoted, this is the quote character, else NUL.  */
 321       int in_quote = 0;
 322
 323       /* Skip whitespace up to the next token.  */
 324       while (*cmdline && isspace (*cmdline))
 325         cmdline ++;
 326       if (*cmdline == 0)
 327         break;
 328
 329       start = cmdline;
 330       /* Check for quoted argument.  */
 331       in_quote = (*cmdline == '\'' || *cmdline == '"') ? *cmdline : 0;
 332
 333       /* Skip to end of token; either by whitespace or matching quote.  */
 334       dprintf (stderr, "in_quote %d\n", in_quote);
 335       while (*cmdline
 336              && (!isspace (*cmdline) || in_quote))
 337         {
 338           if (*cmdline == in_quote
 339               && cmdline != start)
 340             in_quote = 0;
 341           dprintf (stderr, "[%c]%d ", *cmdline, in_quote);
 342           cmdline ++;
 343         }
 344       dprintf (stderr, "\n");
 345
 346       /* Allocate space for this token and store it in args[].  */
 347       end = cmdline;
 348       dprintf (stderr, "start<%s> end<%s>\n", start, end);
 349       args[ap] = (char *) xmalloc (end - start + 1);
 350       memcpy (args[ap], start, end - start);
 351       args[ap][end - start] = 0;
 352
 353       /* Strip off quotes, if found.  */
 354       dprintf (stderr, "args[%d] = <%s>\n", ap, args[ap]);
 355       if (args[ap][0] == '\''
 356           && args[ap][strlen (args[ap])-1] == '\'')
 357         {
 358           args[ap][strlen (args[ap])-1] = 0;
 359           args[ap] ++;
 360         }
 361
 362       else if (args[ap][0] == '"'
 363           && args[ap][strlen (args[ap])-1] == '"')
 364         {
 365           args[ap][strlen (args[ap])-1] = 0;
 366           args[ap] ++;
 367         }
 368
 369       /* Replace positional parameters like $4.  */
 370       else if (args[ap][0] == '$'
 371                && isdigit (args[ap][1])
 372                && args[ap][2] == 0)
 373         {
 374           int a = args[ap][1] - '1';
 375           if (0 <= a && a < nargs)
 376             args[ap] = strdup (iargs[a]);
 377         }
 378
 379       ap ++;
 380
 381       if (*cmdline == 0)
 382         break;
 383     }
 384
 385   /* Lastly, NULL terminate the array and run it.  */
 386   args[ap] = NULL;
 387   run_command_array (args);
 388 }
 389
 390 /* Run a script by reading lines and passing them to the above
 391    function.  */
 392 static void
 393 run_script (const char *filename, const char **args)
 394 {
 395   char line[MAX_LINE_LENGTH + 1];
 396   dprintf (stderr, "run_script starting: '%s'\n", filename);
 397   FILE *f = fopen (filename, "r");
 398   if (f == NULL)
 399     {
 400       fprintf (stderr, "sh: %s: %s\n", filename, strerror (errno));
 401       exit (1);
 402     }
 403   while (fgets (line, sizeof (line), f) != NULL)
 404     {
 405       if (line[0] == '#')
 406         {
 407           dprintf (stderr, "comment: %s\n", line);
 408           continue;
 409         }
 410       run_command_string (line, args);
 411     }
 412   fclose (f);
 413 }
 414
 415 int
 416 main (int argc, const char **argv)
 417 {
 418   int i;
 419
 420   if (strcmp (argv[1], "--debug") == 0)
 421     {
 422       debug_mode = 1;
 423       --argc;
 424       ++argv;
 425     }
 426
 427   dprintf (stderr, "container-sh starting:\n");
 428   for (i = 0; i < argc; i++)
 429     dprintf (stderr, "  argv[%d] is `%s'\n", i, argv[i]);
 430
 431   if (strcmp (argv[1], "-c") == 0)
 432     run_command_string (argv[2], argv+3);
 433   else
 434     run_script (argv[1], argv+2);
 435
 436   dprintf (stderr, "normal exit 0\n");
 437   return 0;
 438 }