login-utils/newgrp.c

   1 /* setgrp.c - by Michael Haardt. Set the gid if possible
   2  * Added a bit more error recovery/reporting - poe
   3  * Vesa Roukonen added code for asking password */
   4
   5 /* 1999-02-22 Arkadiusz Miśkiewicz <misiek@pld.ORG.PL>
   6  * - added Native Language Support
   7  */
   8
   9 #include <errno.h>
  10 #include <getopt.h>
  11 #include <grp.h>
  12 #include <pwd.h>
  13 #include <stdio.h>
  14 #include <stdlib.h>
  15 #include <string.h>
  16 #include <termios.h>
  17 #include <unistd.h>
  18
  19 #ifdef HAVE_CRYPT_H
  20 # include <crypt.h>
  21 #endif
  22
  23 #ifdef HAVE_GETSGNAM
  24 # include <gshadow.h>
  25 #endif
  26
  27 #include "c.h"
  28 #include "closestream.h"
  29 #include "nls.h"
  30 #include "pathnames.h"
  31 #include "xalloc.h"
  32
  33 static char *xgetpass(FILE *input, const char *prompt)
  34 {
  35         char *pass = NULL;
  36         struct termios saved, no_echo;
  37         const int fd = fileno(input);
  38         size_t dummy = 0;
  39         ssize_t len;
  40
  41         fputs(prompt, stdout);
  42         if (isatty(fd)) {
  43                 /* disable echo */
  44                 tcgetattr(fd, &saved);
  45                 no_echo = saved;
  46                 no_echo.c_lflag &= ~ECHO;
  47                 no_echo.c_lflag |= ECHONL;
  48                 if (tcsetattr(fd, TCSANOW, &no_echo))
  49                         err(EXIT_FAILURE, _("could not set terminal attributes"));
  50         }
  51         len = getline(&pass, &dummy, input);
  52         if (isatty(fd))
  53                 /* restore terminal */
  54                 if (tcsetattr(fd, TCSANOW, &saved))
  55                         err(EXIT_FAILURE, _("could not set terminal attributes"));
  56         if (len < 0)
  57                 err(EXIT_FAILURE, _("getline() failed"));
  58         if (0 < len && *(pass + len - 1) == '\n')
  59                 *(pass + len - 1) = '\0';
  60         return pass;
  61 }
  62
  63 #ifndef HAVE_EXPLICIT_BZERO
  64 /* Ensure memory is set to value c without compiler optimization getting
  65  * into way that could happen with memset(3). */
  66 static int xmemset_s(void *v, size_t sz, const int c)
  67 {
  68         volatile unsigned char *p = v;
  69
  70         if (v == NULL)
  71                 return EINVAL;
  72         while (sz--)
  73                 *p++ = c;
  74         return 0;
  75 }
  76 #endif
  77
  78 /* try to read password from gshadow */
  79 static char *get_gshadow_pwd(const char *groupname)
  80 {
  81 #ifdef HAVE_GETSGNAM
  82         struct sgrp *sgrp;
  83
  84         sgrp = getsgnam(groupname);
  85         return sgrp ? xstrdup(sgrp->sg_passwd) : NULL;
  86 #else
  87         char buf[BUFSIZ];
  88         char *pwd = NULL;
  89         FILE *f;
  90
  91         if (groupname == NULL || *groupname == '\0')
  92                 return NULL;
  93
  94         f = fopen(_PATH_GSHADOW, "r");
  95         if (!f)
  96                 return NULL;
  97
  98         while (fgets(buf, sizeof buf, f)) {
  99                 char *cp = strchr(buf, ':');
 100                 if (!cp)
 101                         /* any junk in gshadow? */
 102                         continue;
 103                 *cp = '\0';
 104                 if (strcmp(buf, groupname) == 0) {
 105                         if (cp - buf >= BUFSIZ)
 106                                 /* only group name on line */
 107                                 break;
 108                         pwd = cp + 1;
 109                         if ((cp = strchr(pwd, ':')) && pwd == cp + 1)
 110                                 /* empty password */
 111                                 pwd = NULL;
 112                         else if (cp)
 113                                 *cp = '\0';
 114                         break;
 115                 }
 116         }
 117         fclose(f);
 118         return pwd ? xstrdup(pwd) : NULL;
 119 #endif  /* HAVE_GETSGNAM */
 120 }
 121
 122 static int allow_setgid(const struct passwd *pe, const struct group *ge)
 123 {
 124         char **look;
 125         int notfound = 1;
 126         char *pwd, *xpwd;
 127
 128         if (getuid() == 0)
 129                 /* root may do anything */
 130                 return TRUE;
 131         if (ge->gr_gid == pe->pw_gid)
 132                 /* You can switch back to your default group */
 133                 return TRUE;
 134
 135         look = ge->gr_mem;
 136         while (*look && (notfound = strcmp(*look++, pe->pw_name))) ;
 137
 138         if (!notfound)
 139                 /* member of group => OK */
 140                 return TRUE;
 141
 142         /* Ask for password. Often there is no password in /etc/group, so
 143          * contrary to login et al. we let an empty password mean the same
 144          * as in /etc/passwd */
 145
 146         /* check /etc/gshadow */
 147         if (!(pwd = get_gshadow_pwd(ge->gr_name)))
 148                 pwd = ge->gr_passwd;
 149
 150         if (pwd && *pwd && (xpwd = xgetpass(stdin, _("Password: ")))) {
 151                 char *cbuf = crypt(xpwd, pwd);
 152
 153 #ifdef HAVE_EXPLICIT_BZERO
 154                 explicit_bzero(xpwd, strlen(xpwd));
 155 #else
 156                 xmemset_s(xpwd, strlen(xpwd), 0);
 157 #endif
 158                 free(xpwd);
 159                 if (!cbuf)
 160                         warn(_("crypt failed"));
 161                 else if (strcmp(pwd, cbuf) == 0)
 162                         return TRUE;
 163         }
 164
 165         /* default to denial */
 166         return FALSE;
 167 }
 168
 169 static void __attribute__((__noreturn__)) usage(void)
 170 {
 171         FILE *out = stdout;
 172         fputs(USAGE_HEADER, out);
 173         fprintf(out, _(" %s <group>\n"), program_invocation_short_name);
 174
 175         fputs(USAGE_SEPARATOR, out);
 176         fputs(_("Log in to a new group.\n"), out);
 177
 178         fputs(USAGE_OPTIONS, out);
 179         printf(USAGE_HELP_OPTIONS(16));
 180         printf(USAGE_MAN_TAIL("newgrp(1)"));
 181         exit(EXIT_SUCCESS);
 182 }
 183
 184 int main(int argc, char *argv[])
 185 {
 186         struct passwd *pw_entry;
 187         struct group *gr_entry;
 188         char *shell;
 189         int ch;
 190         static const struct option longopts[] = {
 191                 {"version", no_argument, NULL, 'V'},
 192                 {"help", no_argument, NULL, 'h'},
 193                 {NULL, 0, NULL, 0}
 194         };
 195
 196         setlocale(LC_ALL, "");
 197         bindtextdomain(PACKAGE, LOCALEDIR);
 198         textdomain(PACKAGE);
 199         close_stdout_atexit();
 200
 201         while ((ch = getopt_long(argc, argv, "Vh", longopts, NULL)) != -1)
 202                 switch (ch) {
 203                 case 'V':
 204                         print_version(EXIT_SUCCESS);
 205                 case 'h':
 206                         usage();
 207                 default:
 208                         errtryhelp(EXIT_FAILURE);
 209                 }
 210
 211         if (!(pw_entry = getpwuid(getuid())))
 212                 err(EXIT_FAILURE, _("who are you?"));
 213
 214         if (argc < 2) {
 215                 if (setgid(pw_entry->pw_gid) < 0)
 216                         err(EXIT_FAILURE, _("setgid failed"));
 217         } else {
 218                 errno = 0;
 219                 if (!(gr_entry = getgrnam(argv[1]))) {
 220                         if (errno)
 221                                 err(EXIT_FAILURE, _("no such group"));
 222                         else
 223                                 errx(EXIT_FAILURE, _("no such group"));
 224                 }
 225                 if (!allow_setgid(pw_entry, gr_entry))
 226                         errx(EXIT_FAILURE, _("permission denied"));
 227                 if (setgid(gr_entry->gr_gid) < 0)
 228                         err(EXIT_FAILURE, _("setgid failed"));
 229         }
 230
 231         if (setuid(getuid()) < 0)
 232                 err(EXIT_FAILURE, _("setuid failed"));
 233
 234         fflush(NULL);
 235         shell = (pw_entry->pw_shell && *pw_entry->pw_shell ?
 236                                 pw_entry->pw_shell : _PATH_BSHELL);
 237         execl(shell, shell, (char *)0);
 238         errexec(shell);
 239 }