release/src/router/busybox/libbb/safe_gethostname.c

   1 /* vi: set sw=4 ts=4: */
   2 /*
   3  * Safe gethostname implementation for busybox
   4  *
   5  * Copyright (C) 2008 Tito Ragusa <farmatito@tiscali.it>
   6  *
   7  * Licensed under GPLv2 or later, see file LICENSE in this source tree.
   8  */
   9
  10 /*
  11  * SUSv2 guarantees that "Host names are limited to 255 bytes"
  12  * POSIX.1-2001 guarantees that "Host names (not including the terminating
  13  * null byte) are limited to HOST_NAME_MAX bytes" (64 bytes on my box).
  14  *
  15  * RFC1123 says:
  16  *
  17  * The syntax of a legal Internet host name was specified in RFC-952
  18  * [DNS:4].  One aspect of host name syntax is hereby changed: the
  19  * restriction on the first character is relaxed to allow either a
  20  * letter or a digit.  Host software MUST support this more liberal
  21  * syntax.
  22  *
  23  * Host software MUST handle host names of up to 63 characters and
  24  * SHOULD handle host names of up to 255 characters.
  25  */
  26
  27 #include "libbb.h"
  28 #include <sys/utsname.h>
  29
  30 /*
  31  * On success return the current malloced and NUL terminated hostname.
  32  * On error return malloced and NUL terminated string "?".
  33  * This is an illegal first character for a hostname.
  34  * The returned malloced string must be freed by the caller.
  35  */
  36 char* FAST_FUNC safe_gethostname(void)
  37 {
  38         struct utsname uts;
  39
  40         /* The length of the arrays in a struct utsname is unspecified;
  41          * the fields are terminated by a null byte.
  42          * Note that there is no standard that says that the hostname
  43          * set by sethostname(2) is the same string as the nodename field of the
  44          * struct returned by uname (indeed, some systems allow a 256-byte host-
  45          * name and an 8-byte nodename), but this is true on Linux. The same holds
  46          * for setdomainname(2) and the domainname field.
  47          */
  48
  49         /* Uname can fail only if you pass a bad pointer to it. */
  50         uname(&uts);
  51         return xstrndup(!uts.nodename[0] ? "?" : uts.nodename, sizeof(uts.nodename));
  52 }