fusl/src/passwd/getspnam_r.c

#include <fcntl.h>
#include <unistd.h>
#include <sys/stat.h>
#include <ctype.h>
#include <pthread.h>
#include "pwf.h"

/* This implementation support Openwall-style TCB passwords in place of
 * traditional shadow, if the appropriate directories and files exist.
 * Thus, it is careful to avoid following symlinks or blocking on fifos
 * which a malicious user might create in place of his or her TCB shadow
 * file. It also avoids any allocation to prevent memory-exhaustion
 * attacks via huge TCB shadow files. */

static long xatol(char** s) {
  long x;
  if (**s == ':' || **s == '\n')
    return -1;
  for (x = 0; **s - '0' < 10U; ++*s)
    x = 10 * x + (**s - '0');
  return x;
}

int __parsespent(char* s, struct spwd* sp) {
  sp->sp_namp = s;
  if (!(s = strchr(s, ':')))
    return -1;
  *s = 0;

  sp->sp_pwdp = ++s;
  if (!(s = strchr(s, ':')))
    return -1;
  *s = 0;

  s++;
  sp->sp_lstchg = xatol(&s);
  if (*s != ':')
    return -1;

  s++;
  sp->sp_min = xatol(&s);
  if (*s != ':')
    return -1;

  s++;
  sp->sp_max = xatol(&s);
  if (*s != ':')
    return -1;

  s++;
  sp->sp_warn = xatol(&s);
  if (*s != ':')
    return -1;

  s++;
  sp->sp_inact = xatol(&s);
  if (*s != ':')
    return -1;

  s++;
  sp->sp_expire = xatol(&s);
  if (*s != ':')
    return -1;

  s++;
  sp->sp_flag = xatol(&s);
  if (*s != '\n')
    return -1;
  return 0;
}

static void cleanup(void* p) {
  fclose(p);
}

int getspnam_r(const char* name,
               struct spwd* sp,
               char* buf,
               size_t size,
               struct spwd** res) {
  char path[20 + NAME_MAX];
  FILE* f = 0;
  int rv = 0;
  int fd;
  size_t k, l = strlen(name);
  int skip = 0;
  int cs;

  *res = 0;

  /* Disallow potentially-malicious user names */
  if (*name == '.' || strchr(name, '/') || !l)
    return EINVAL;

  /* Buffer size must at least be able to hold name, plus some.. */
  if (size < l + 100)
    return ERANGE;

  /* Protect against truncation */
  if (snprintf(path, sizeof path, "/etc/tcb/%s/shadow", name) >= sizeof path)
    return EINVAL;

  fd = open(path, O_RDONLY | O_NOFOLLOW | O_NONBLOCK | O_CLOEXEC);
  if (fd >= 0) {
    struct stat st = {0};
    errno = EINVAL;
    if (fstat(fd, &st) || !S_ISREG(st.st_mode) || !(f = fdopen(fd, "rb"))) {
      pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
      close(fd);
      pthread_setcancelstate(cs, 0);
      return errno;
    }
  } else {
    f = fopen("/etc/shadow", "rbe");
    if (!f)
      return errno;
  }

  pthread_cleanup_push(cleanup, f);
  while (fgets(buf, size, f) && (k = strlen(buf)) > 0) {
    if (skip || strncmp(name, buf, l) || buf[l] != ':') {
      skip = buf[k - 1] != '\n';
      continue;
    }
    if (buf[k - 1] != '\n') {
      rv = ERANGE;
      break;
    }

    if (__parsespent(buf, sp) < 0)
      continue;
    *res = sp;
    break;
  }
  pthread_cleanup_pop(1);
  return rv;
}