support/shell-container.c

   1 /* Minimal /bin/sh for in-container use.
   2    Copyright (C) 2018 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 #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, dfd;
  97   struct stat st;
  98
  99   sfd = open (sname, O_RDONLY);
 100   if (sfd < 0)
 101     {
 102       fprintf (stderr, "cp: unable to open %s for reading: %s\n",
 103                sname, strerror (errno));
 104       return 1;
 105     }
 106
 107   if (fstat (sfd, &st) < 0)
 108     {
 109       fprintf (stderr, "cp: unable to fstat %s: %s\n",
 110                sname, strerror (errno));
 111       return 1;
 112     }
 113
 114   dfd = open (dname, O_WRONLY | O_TRUNC | O_CREAT, 0600);
 115   if (dfd < 0)
 116     {
 117       fprintf (stderr, "cp: unable to open %s for writing: %s\n",
 118                dname, strerror (errno));
 119       return 1;
 120     }
 121
 122   if (copy_file_range (sfd, 0, dfd, 0, st.st_size, 0) != st.st_size)
 123     {
 124       fprintf (stderr, "cp: cannot copy file %s to %s: %s\n",
 125                sname, dname, strerror (errno));
 126       return 1;
 127     }
 128
 129   close (sfd);
 130   close (dfd);
 131
 132   chmod (dname, st.st_mode & 0777);
 133
 134   return 0;
 135
 136 }
 137
 138 /* This is a list of all the built-in commands we understand.  */
 139 static struct {
 140   const char *name;
 141   int (*func) (char **argv);
 142 } builtin_funcs[] = {
 143   { "true", true_func },
 144   { "echo", echo_func },
 145   { "cp", copy_func },
 146   { NULL, NULL }
 147 };
 148
 149 /* Run one tokenized command.  argv[0] is the command.  argv is
 150    NULL-terminated.  */
 151 static void
 152 run_command_array (char **argv)
 153 {
 154   int i, j;
 155   pid_t pid;
 156   int status;
 157   int (*builtin_func) (char **args);
 158
 159   if (argv[0] == NULL)
 160     return;
 161
 162   builtin_func = NULL;
 163
 164   int new_stdin = 0;
 165   int new_stdout = 1;
 166   int new_stderr = 2;
 167
 168   dprintf (stderr, "run_command_array starting\n");
 169   for (i = 0; argv[i]; i++)
 170     dprintf (stderr, "   argv [%d] `%s'\n", i, argv[i]);
 171
 172   for (j = i = 0; argv[i]; i++)
 173     {
 174       if (strcmp (argv[i], "<") == 0 && argv[i + 1])
 175         {
 176           new_stdin = open (argv[i + 1], O_WRONLY|O_CREAT|O_TRUNC, 0777);
 177           ++i;
 178           continue;
 179         }
 180       if (strcmp (argv[i], ">") == 0 && argv[i + 1])
 181         {
 182           new_stdout = open (argv[i + 1], O_WRONLY|O_CREAT|O_TRUNC, 0777);
 183           ++i;
 184           continue;
 185         }
 186       if (strcmp (argv[i], ">>") == 0 && argv[i + 1])
 187         {
 188           new_stdout = open (argv[i + 1], O_WRONLY|O_CREAT|O_APPEND, 0777);
 189           ++i;
 190           continue;
 191         }
 192       if (strcmp (argv[i], "2>") == 0 && argv[i + 1])
 193         {
 194           new_stderr = open (argv[i + 1], O_WRONLY|O_CREAT|O_TRUNC, 0777);
 195           ++i;
 196           continue;
 197         }
 198       argv[j++] = argv[i];
 199     }
 200   argv[j] = NULL;
 201
 202
 203   for (i = 0; builtin_funcs[i].name != NULL; i++)
 204     if (strcmp (argv[0], builtin_funcs[i].name) == 0)
 205        builtin_func = builtin_funcs[i].func;
 206
 207   dprintf (stderr, "builtin %p argv0 `%s'\n", builtin_func, argv[0]);
 208
 209   pid = fork ();
 210   if (pid < 0)
 211     {
 212       fprintf (stderr, "sh: fork failed\n");
 213       exit (1);
 214     }
 215
 216   if (pid == 0)
 217     {
 218       if (new_stdin != 0)
 219         {
 220           dup2 (new_stdin, 0);
 221           close (new_stdin);
 222         }
 223       if (new_stdout != 1)
 224         {
 225           dup2 (new_stdout, 1);
 226           close (new_stdout);
 227         }
 228       if (new_stderr != 2)
 229         {
 230           dup2 (new_stderr, 2);
 231           close (new_stdout);
 232         }
 233
 234       if (builtin_func != NULL)
 235         exit (builtin_func (argv + 1));
 236
 237       execvp (argv[0], argv);
 238
 239       fprintf (stderr, "sh: execing %s failed: %s",
 240                argv[0], strerror (errno));
 241       exit (1);
 242     }
 243
 244   waitpid (pid, &status, 0);
 245
 246   dprintf (stderr, "exiting run_command_array\n");
 247
 248   if (WIFEXITED (status))
 249     {
 250       int rv = WEXITSTATUS (status);
 251       if (rv)
 252         exit (rv);
 253     }
 254   else
 255     exit (1);
 256 }
 257
 258 /* Run one command-as-a-string, by tokenizing it.  Limited to
 259    MAX_ARG_COUNT arguments.  Simple substitution is done of $1 to $9
 260    (as whole separate tokens) from iargs[].  Quoted strings work if
 261    the quotes wrap whole tokens; i.e. "foo bar" but not foo" bar".  */
 262 static void
 263 run_command_string (const char *cmdline, const char **iargs)
 264 {
 265   char *args[MAX_ARG_COUNT+1];
 266   int ap = 0;
 267   const char *start, *end;
 268   int nargs;
 269
 270   for (nargs = 0; iargs[nargs] != NULL; ++nargs)
 271     ;
 272
 273   dprintf (stderr, "run_command_string starting: '%s'\n", cmdline);
 274
 275   while (ap < MAX_ARG_COUNT)
 276     {
 277       /* If the argument is quoted, this is the quote character, else NUL.  */
 278       int in_quote = 0;
 279
 280       /* Skip whitespace up to the next token.  */
 281       while (*cmdline && isspace (*cmdline))
 282         cmdline ++;
 283       if (*cmdline == 0)
 284         break;
 285
 286       start = cmdline;
 287       /* Check for quoted argument.  */
 288       in_quote = (*cmdline == '\'' || *cmdline == '"') ? *cmdline : 0;
 289
 290       /* Skip to end of token; either by whitespace or matching quote.  */
 291       dprintf (stderr, "in_quote %d\n", in_quote);
 292       while (*cmdline
 293              && (!isspace (*cmdline) || in_quote))
 294         {
 295           if (*cmdline == in_quote
 296               && cmdline != start)
 297             in_quote = 0;
 298           dprintf (stderr, "[%c]%d ", *cmdline, in_quote);
 299           cmdline ++;
 300         }
 301       dprintf (stderr, "\n");
 302
 303       /* Allocate space for this token and store it in args[].  */
 304       end = cmdline;
 305       dprintf (stderr, "start<%s> end<%s>\n", start, end);
 306       args[ap] = (char *) xmalloc (end - start + 1);
 307       memcpy (args[ap], start, end - start);
 308       args[ap][end - start] = 0;
 309
 310       /* Strip off quotes, if found.  */
 311       dprintf (stderr, "args[%d] = <%s>\n", ap, args[ap]);
 312       if (args[ap][0] == '\''
 313           && args[ap][strlen (args[ap])-1] == '\'')
 314         {
 315           args[ap][strlen (args[ap])-1] = 0;
 316           args[ap] ++;
 317         }
 318
 319       else if (args[ap][0] == '"'
 320           && args[ap][strlen (args[ap])-1] == '"')
 321         {
 322           args[ap][strlen (args[ap])-1] = 0;
 323           args[ap] ++;
 324         }
 325
 326       /* Replace positional parameters like $4.  */
 327       else if (args[ap][0] == '$'
 328                && isdigit (args[ap][1])
 329                && args[ap][2] == 0)
 330         {
 331           int a = args[ap][1] - '1';
 332           if (0 <= a && a < nargs)
 333             args[ap] = strdup (iargs[a]);
 334         }
 335
 336       ap ++;
 337
 338       if (*cmdline == 0)
 339         break;
 340     }
 341
 342   /* Lastly, NULL terminate the array and run it.  */
 343   args[ap] = NULL;
 344   run_command_array (args);
 345 }
 346
 347 /* Run a script by reading lines and passing them to the above
 348    function.  */
 349 static void
 350 run_script (const char *filename, const char **args)
 351 {
 352   char line[MAX_LINE_LENGTH + 1];
 353   dprintf (stderr, "run_script starting: '%s'\n", filename);
 354   FILE *f = fopen (filename, "r");
 355   if (f == NULL)
 356     {
 357       fprintf (stderr, "sh: %s: %s\n", filename, strerror (errno));
 358       exit (1);
 359     }
 360   while (fgets (line, sizeof (line), f) != NULL)
 361     {
 362       if (line[0] == '#')
 363         {
 364           dprintf (stderr, "comment: %s\n", line);
 365           continue;
 366         }
 367       run_command_string (line, args);
 368     }
 369   fclose (f);
 370 }
 371
 372 int
 373 main (int argc, const char **argv)
 374 {
 375   int i;
 376
 377   if (strcmp (argv[1], "--debug") == 0)
 378     {
 379       debug_mode = 1;
 380       --argc;
 381       ++argv;
 382     }
 383
 384   dprintf (stderr, "container-sh starting:\n");
 385   for (i = 0; i < argc; i++)
 386     dprintf (stderr, "  argv[%d] is `%s'\n", i, argv[i]);
 387
 388   if (strcmp (argv[1], "-c") == 0)
 389     run_command_string (argv[2], argv+3);
 390   else
 391     run_script (argv[1], argv+2);
 392
 393   dprintf (stderr, "normal exit 0\n");
 394   return 0;
 395 }