loginutils/add-remove-shell.c

   1 /*
   2  * add-shell and remove-shell implementation for busybox
   3  *
   4  * Copyright (C) 2010 Nokia Corporation. All rights reserved.
   5  * Written by Alexander Shishkin <virtuoso@slind.org>
   6  *
   7  * Licensed under GPLv2 or later, see the LICENSE file in this source tree
   8  * for details.
   9  */
  10
  11 //applet:IF_ADD_SHELL(   APPLET_ODDNAME(add-shell   , add_remove_shell, BB_DIR_USR_BIN, BB_SUID_DROP, add_shell   ))
  12 //applet:IF_REMOVE_SHELL(APPLET_ODDNAME(remove-shell, add_remove_shell, BB_DIR_USR_BIN, BB_SUID_DROP, remove_shell))
  13
  14 //kbuild:lib-$(CONFIG_ADD_SHELL)    += add-remove-shell.o
  15 //kbuild:lib-$(CONFIG_REMOVE_SHELL) += add-remove-shell.o
  16
  17 //config:config ADD_SHELL
  18 //config:       bool "add-shell"
  19 //config:       default y if DESKTOP
  20 //config:       help
  21 //config:         Add shells to /etc/shells.
  22 //config:
  23 //config:config REMOVE_SHELL
  24 //config:       bool "remove-shell"
  25 //config:       default y if DESKTOP
  26 //config:       help
  27 //config:         Remove shells from /etc/shells.
  28
  29 //usage:#define add_shell_trivial_usage
  30 //usage:       "SHELL..."
  31 //usage:#define add_shell_full_usage "\n\n"
  32 //usage:       "Add SHELLs to /etc/shells"
  33
  34 //usage:#define remove_shell_trivial_usage
  35 //usage:       "SHELL..."
  36 //usage:#define remove_shell_full_usage "\n\n"
  37 //usage:       "Remove SHELLs from /etc/shells"
  38
  39 #include "libbb.h"
  40
  41 #define SHELLS_FILE "/etc/shells"
  42
  43 #define REMOVE_SHELL (ENABLE_REMOVE_SHELL && (!ENABLE_ADD_SHELL || applet_name[0] == 'r'))
  44 #define ADD_SHELL    (ENABLE_ADD_SHELL && (!ENABLE_REMOVE_SHELL || applet_name[0] == 'a'))
  45
  46 /* NB: we use the _address_, not the value, of this string
  47  * as a "special value of pointer" in the code.
  48  */
  49 static const char dont_add[] ALIGN1 = "\n";
  50
  51 int add_remove_shell_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
  52 int add_remove_shell_main(int argc UNUSED_PARAM, char **argv)
  53 {
  54         FILE *orig_fp;
  55         char *orig_fn;
  56         char *new_fn;
  57
  58         argv++;
  59
  60         orig_fn = xmalloc_follow_symlinks(SHELLS_FILE);
  61         if (!orig_fn)
  62                 return EXIT_FAILURE;
  63         orig_fp = fopen_for_read(orig_fn);
  64
  65         new_fn = xasprintf("%s.tmp", orig_fn);
  66         /*
  67          * O_TRUNC or O_EXCL? At the first glance, O_EXCL looks better,
  68          * since it prevents races. But: (1) it requires a retry loop,
  69          * (2) if /etc/shells.tmp is *stale*, then retry loop
  70          * with O_EXCL will never succeed - it should have a timeout,
  71          * after which it should revert to O_TRUNC.
  72          * For now, I settle for O_TRUNC instead.
  73          */
  74         xmove_fd(xopen(new_fn, O_WRONLY | O_CREAT | O_TRUNC), STDOUT_FILENO);
  75
  76         /* TODO:
  77         struct stat sb;
  78         xfstat(fileno(orig_fp), &sb);
  79         xfchown(STDOUT_FILENO, sb.st_uid, sb.st_gid);
  80         xfchmod(STDOUT_FILENO, sb.st_mode);
  81         */
  82
  83         if (orig_fp) {
  84                 /* Copy old file, possibly skipping removed shell names */
  85                 char *line;
  86                 while ((line = xmalloc_fgetline(orig_fp)) != NULL) {
  87                         char **cpp = argv;
  88                         while (*cpp) {
  89                                 if (strcmp(*cpp, line) == 0) {
  90                                         /* Old file has this shell name */
  91                                         if (REMOVE_SHELL) {
  92                                                 /* we are remove-shell */
  93                                                 /* delete this name by not copying it */
  94                                                 goto next_line;
  95                                         }
  96                                         /* we are add-shell */
  97                                         /* mark this name as "do not add" */
  98                                         *cpp = (char*)dont_add;
  99                                 }
 100                                 cpp++;
 101                         }
 102                         /* copy shell name from old to new file */
 103                         printf("%s\n", line);
 104  next_line:
 105                         free(line);
 106                 }
 107                 if (ENABLE_FEATURE_CLEAN_UP)
 108                         fclose(orig_fp);
 109         }
 110
 111         if (ADD_SHELL) {
 112                 char **cpp = argv;
 113                 while (*cpp) {
 114                         if (*cpp != dont_add)
 115                                 printf("%s\n", *cpp);
 116                         cpp++;
 117                 }
 118         }
 119
 120         /* Ensure we wrote out everything */
 121         if (fclose(stdout) != 0) {
 122                 xunlink(new_fn);
 123                 bb_perror_msg_and_die("%s: write error", new_fn);
 124         }
 125
 126         /* Small hole: if rename fails, /etc/shells.tmp is not removed */
 127         xrename(new_fn, orig_fn);
 128
 129         if (ENABLE_FEATURE_CLEAN_UP) {
 130                 free(orig_fn);
 131                 free(new_fn);
 132         }
 133
 134         return EXIT_SUCCESS;
 135 }