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 //config:config ADD_SHELL
  11 //config:       bool "add-shell (3.3 kb)"
  12 //config:       default y if DESKTOP
  13 //config:       help
  14 //config:       Add shells to /etc/shells.
  15 //config:
  16 //config:config REMOVE_SHELL
  17 //config:       bool "remove-shell (3.3 kb)"
  18 //config:       default y if DESKTOP
  19 //config:       help
  20 //config:       Remove shells from /etc/shells.
  21
  22 //                       APPLET_NOEXEC:name          main              location         suid_type     help
  23 //applet:IF_ADD_SHELL(   APPLET_NOEXEC(add-shell   , add_remove_shell, BB_DIR_USR_SBIN, BB_SUID_DROP, add_shell   ))
  24 //applet:IF_REMOVE_SHELL(APPLET_NOEXEC(remove-shell, add_remove_shell, BB_DIR_USR_SBIN, BB_SUID_DROP, remove_shell))
  25
  26 //kbuild:lib-$(CONFIG_ADD_SHELL)    += add-remove-shell.o
  27 //kbuild:lib-$(CONFIG_REMOVE_SHELL) += add-remove-shell.o
  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 #define dont_add ((char*)(uintptr_t)1)
  47
  48 int add_remove_shell_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
  49 int add_remove_shell_main(int argc UNUSED_PARAM, char **argv)
  50 {
  51         FILE *orig_fp;
  52         char *orig_fn;
  53         char *new_fn;
  54         struct stat sb;
  55
  56         sb.st_mode = 0666;
  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         if (orig_fp)
  65                 xfstat(fileno(orig_fp), &sb, orig_fn);
  66
  67
  68         new_fn = xasprintf("%s.tmp", orig_fn);
  69         /*
  70          * O_TRUNC or O_EXCL? At the first glance, O_EXCL looks better,
  71          * since it prevents races. But: (1) it requires a retry loop,
  72          * (2) if /etc/shells.tmp is *stale*, then retry loop
  73          * with O_EXCL will never succeed - it should have a timeout,
  74          * after which it should revert to O_TRUNC.
  75          * For now, I settle for O_TRUNC instead.
  76          */
  77         xmove_fd(xopen3(new_fn, O_WRONLY | O_CREAT | O_TRUNC, sb.st_mode), STDOUT_FILENO);
  78         /* TODO?
  79         xfchown(STDOUT_FILENO, sb.st_uid, sb.st_gid);
  80         */
  81
  82         if (orig_fp) {
  83                 /* Copy old file, possibly skipping removed shell names */
  84                 char *line;
  85                 while ((line = xmalloc_fgetline(orig_fp)) != NULL) {
  86                         char **cpp = argv;
  87                         while (*cpp) {
  88                                 if (*cpp != dont_add && strcmp(*cpp, line) == 0) {
  89                                         /* Old file has this shell name */
  90                                         if (REMOVE_SHELL) {
  91                                                 /* we are remove-shell */
  92                                                 /* delete this name by not copying it */
  93                                                 goto next_line;
  94                                         }
  95                                         /* we are add-shell */
  96                                         /* mark this name as "do not add" */
  97                                         *cpp = dont_add;
  98                                 }
  99                                 cpp++;
 100                         }
 101                         /* copy shell name from old to new file */
 102                         puts(line);
 103  next_line:
 104                         free(line);
 105                 }
 106                 if (ENABLE_FEATURE_CLEAN_UP)
 107                         fclose(orig_fp);
 108         }
 109
 110         if (ADD_SHELL) {
 111                 char **cpp = argv;
 112                 while (*cpp) {
 113                         if (*cpp != dont_add)
 114                                 puts(*cpp);
 115                         cpp++;
 116                 }
 117         }
 118
 119         /* Ensure we wrote out everything */
 120         if (fclose(stdout) != 0) {
 121                 xunlink(new_fn);
 122                 bb_perror_msg_and_die("%s: write error", new_fn);
 123         }
 124
 125         /* Small hole: if rename fails, /etc/shells.tmp is not removed */
 126         xrename(new_fn, orig_fn);
 127
 128         if (ENABLE_FEATURE_CLEAN_UP) {
 129                 free(orig_fn);
 130                 free(new_fn);
 131         }
 132
 133         return EXIT_SUCCESS;
 134 }