lib/password.c

/* password.c - password read/update helper functions.
 *
 * Copyright 2012 Ashwini Kumar <ak.ashwini@gmail.com>
 */

#include "toys.h"
#include <time.h>

int get_salt(char *salt, char *algo)
{      
  int i, len = 0, offset = 0;
  char buf[12];

  if (!strcmp(algo,"des")) len = 2;
  else {
    *salt++ = '$';
    if (!strcmp(algo,"md5")) {
      *salt++ = '1';
      len = 8;
    } else if (!strcmp(algo,"sha256")) {
      *salt++ = '5';
      len = 16;
    } else if (!strcmp(algo,"sha512")) {
      *salt++ = '6';
      len = 16;
    } else return -1;

    *salt++ = '$';
    offset = 3;
  }    

  // Read appropriate number of random bytes for salt
  i = xopen("/dev/urandom", O_RDONLY);
  xreadall(i, buf, ((len*6)+7)/8);
  close(i);

  // Grab 6 bit chunks and convert to characters in ./0-9a-zA-Z
  for (i=0; i<len; i++) {
    int bitpos = i*6, bits = bitpos/8;

    bits = ((buf[i]+(buf[i+1]<<8)) >> (bitpos&7)) & 0x3f;
    bits += 46;
    if (bits > 57) bits += 7;
    if (bits > 90) bits += 6;

    salt[i] = bits;
  }
  salt[i] = 0;

  return offset;
}

static void handle(int signo)
{
  //Dummy.. so that read breaks on the signal, 
  //instead of the applocation exit
}

int read_password(char * buff, int buflen, char* mesg)
{
  int i = 0;
  struct termios termio, oldtermio;
  struct sigaction sa, oldsa;

  tcgetattr(0, &oldtermio);
  tcflush(0, TCIFLUSH);
  termio = oldtermio;

  memset(&sa, 0, sizeof(sa));
  sa.sa_handler = handle;
  sigaction(SIGINT, &sa, &oldsa);

  termio.c_iflag &= ~(IUCLC|IXON|IXOFF|IXANY);
  termio.c_lflag &= ~(ECHO|ECHOE|ECHOK|ECHONL|TOSTOP);
  tcsetattr(0, TCSANOW, &termio);

  fputs(mesg, stdout);
  fflush(stdout);

  while (1) {
    int ret = read(0, &buff[i], 1);
    if ( ret < 0 ) {
      buff[0] = 0;
      sigaction(SIGINT, &oldsa, NULL);
      tcsetattr(0, TCSANOW, &oldtermio);
      xputc('\n');
      fflush(stdout);
      return 1;
    } else if (ret == 0 || buff[i] == '\n' || buff[i] == '\r' || buflen == i+1)
    {
      buff[i] = '\0';
      break;
    }
    i++;
  }
  sigaction(SIGINT, &oldsa, NULL);
  tcsetattr(0, TCSANOW, &oldtermio);
  puts("");
  fflush(stdout);
  return 0;
}

static char *get_nextcolon(char *line, int cnt)
{
  while (cnt--) {
    if (!(line = strchr(line, ':'))) error_exit("Invalid Entry\n");
    line++; //jump past the colon
  }
  return line;
}

/*update_password is used by multiple utilities to update /etc/passwd,
 * /etc/shadow, /etc/group and /etc/gshadow files, 
 * which are used as user, group databeses
 * entry can be 
 * 1. encrypted password, when updating user password.
 * 2. complete entry for user details, when creating new user
 * 3. group members comma',' separated list, when adding user to group
 * 4. complete entry for group details, when creating new group
 * 5. entry = NULL, delete the named entry user/group
 */
int update_password(char *filename, char* username, char* entry)
{
  char *filenamesfx = NULL, *namesfx = NULL, *shadow = NULL,
       *sfx = NULL, *line = NULL;
  FILE *exfp, *newfp;
  int ret = -1, found = 0;
  struct flock lock;

  shadow = strstr(filename, "shadow");
  filenamesfx = xmprintf("%s+", filename);
  sfx = strchr(filenamesfx, '+');

  exfp = fopen(filename, "r+");
  if (!exfp) {
    perror_msg("Couldn't open file %s",filename);
    goto free_storage;
  }

  *sfx = '-';
  ret = unlink(filenamesfx);
  ret = link(filename, filenamesfx);
  if (ret < 0) error_msg("can't create backup file");

  *sfx = '+';
  lock.l_type = F_WRLCK;
  lock.l_whence = SEEK_SET;
  lock.l_start = 0;
  lock.l_len = 0;

  ret = fcntl(fileno(exfp), F_SETLK, &lock);
  if (ret < 0) perror_msg("Couldn't lock file %s",filename);

  lock.l_type = F_UNLCK; //unlocking at a later stage

  newfp = fopen(filenamesfx, "w+");
  if (!newfp) {
    error_msg("couldn't open file for writing");
    ret = -1;
    fclose(exfp);
    goto free_storage;
  }

  ret = 0;
  namesfx = xmprintf("%s:",username);
  while ((line = get_line(fileno(exfp))) != NULL)
  {
    if (strncmp(line, namesfx, strlen(namesfx)))
      fprintf(newfp, "%s\n", line);
    else if (entry) {
      char *current_ptr = NULL;

      found = 1;
      if (!strcmp(toys.which->name, "passwd")) {
        fprintf(newfp, "%s%s:",namesfx, entry);
        current_ptr = get_nextcolon(line, 2); //past passwd
        if (shadow) {
          fprintf(newfp, "%u:",(unsigned)(time(NULL))/(24*60*60));
          current_ptr = get_nextcolon(current_ptr, 1);
          fprintf(newfp, "%s\n",current_ptr);
        } else fprintf(newfp, "%s\n",current_ptr);
      } else if (!strcmp(toys.which->name, "groupadd") || 
          !strcmp(toys.which->name, "addgroup") ||
          !strcmp(toys.which->name, "delgroup") ||
          !strcmp(toys.which->name, "groupdel")){
        current_ptr = get_nextcolon(line, 3); //past gid/admin list
        *current_ptr = '\0';
        fprintf(newfp, "%s", line);
        fprintf(newfp, "%s\n", entry);
      }
    }
    free(line);
  }
  free(namesfx);
  if (!found && entry) fprintf(newfp, "%s\n", entry);
  fcntl(fileno(exfp), F_SETLK, &lock);
  fclose(exfp);

  errno = 0;
  fflush(newfp);
  fsync(fileno(newfp));
  fclose(newfp);
  rename(filenamesfx, filename);
  if (errno) {
    perror_msg("File Writing/Saving failed: ");
    unlink(filenamesfx);
    ret = -1;
  }

free_storage:
  free(filenamesfx);
  return ret;
}

void is_valid_username(const char *name)                                                                                              
{
  regex_t rp;
  regmatch_t rm[1]; 
  int eval;
  char *regex = "^[_.A-Za-z0-9][-_.A-Za-z0-9]*"; //User name REGEX

  xregcomp(&rp, regex, REG_NEWLINE);

  /* compare string against pattern --  remember that patterns 
     are anchored to the beginning of the line */
  eval = regexec(&rp, name, 1, rm, 0);
  regfree(&rp);
  if (!eval && !rm[0].rm_so) {
    int len = strlen(name);
    if ((rm[0].rm_eo == len) ||
        (rm[0].rm_eo == len - 1 && name[len - 1] == '$')) {
      if (len >= LOGIN_NAME_MAX) error_exit("name is too long");
      else return;
    }
  }
  error_exit("'%s', not valid %sname",name,
      (((toys.which->name[3] == 'g') || 
        (toys.which->name[0] == 'g'))? "group" : "user"));
}