sysdeps/unix/sysv/linux/getlogin_r.c

   1 /* Copyright (C) 2010-2017 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <http://www.gnu.org/licenses/>.  */
  17
  18 #include <pwd.h>
  19 #include <unistd.h>
  20 #include <not-cancel.h>
  21
  22 #define STATIC static
  23 static int getlogin_r_fd0 (char *name, size_t namesize);
  24 #define __getlogin_r getlogin_r_fd0
  25 #include <sysdeps/unix/getlogin_r.c>
  26 #undef __getlogin_r
  27
  28
  29 /* Try to determine login name from /proc/self/loginuid and return 0
  30    if successful.  If /proc/self/loginuid cannot be read return -1.
  31    Otherwise return the error number.  */
  32
  33 int
  34 attribute_hidden
  35 __getlogin_r_loginuid (char *name, size_t namesize)
  36 {
  37   int fd = __open_nocancel ("/proc/self/loginuid", O_RDONLY);
  38   if (fd == -1)
  39     return -1;
  40
  41   /* We are reading a 32-bit number.  12 bytes are enough for the text
  42      representation.  If not, something is wrong.  */
  43   char uidbuf[12];
  44   ssize_t n = TEMP_FAILURE_RETRY (__read_nocancel (fd, uidbuf,
  45                                                    sizeof (uidbuf)));
  46   __close_nocancel_nostatus (fd);
  47
  48   uid_t uid;
  49   char *endp;
  50   if (n <= 0
  51       || n == sizeof (uidbuf)
  52       || (uidbuf[n] = '\0',
  53           uid = strtoul (uidbuf, &endp, 10),
  54           endp == uidbuf || *endp != '\0'))
  55     return -1;
  56
  57   size_t buflen = 1024;
  58   char *buf = alloca (buflen);
  59   bool use_malloc = false;
  60   struct passwd pwd;
  61   struct passwd *tpwd;
  62   int result = 0;
  63   int res;
  64
  65   while ((res = __getpwuid_r (uid, &pwd, buf, buflen, &tpwd)) == ERANGE)
  66     if (__libc_use_alloca (2 * buflen))
  67       buf = extend_alloca (buf, buflen, 2 * buflen);
  68     else
  69       {
  70         buflen *= 2;
  71         char *newp = realloc (use_malloc ? buf : NULL, buflen);
  72         if (newp == NULL)
  73           {
  74             result = ENOMEM;
  75             goto out;
  76           }
  77         buf = newp;
  78         use_malloc = true;
  79       }
  80
  81   if (res != 0 || tpwd == NULL)
  82     {
  83       result = -1;
  84       goto out;
  85     }
  86
  87   size_t needed = strlen (pwd.pw_name) + 1;
  88   if (needed > namesize)
  89     {
  90       __set_errno (ERANGE);
  91       result = ERANGE;
  92       goto out;
  93     }
  94
  95   memcpy (name, pwd.pw_name, needed);
  96
  97  out:
  98   if (use_malloc)
  99     free (buf);
 100
 101   return result;
 102 }
 103
 104
 105 /* Return at most NAME_LEN characters of the login name of the user in NAME.
 106    If it cannot be determined or some other error occurred, return the error
 107    code.  Otherwise return 0.  */
 108
 109 int
 110 __getlogin_r (char *name, size_t namesize)
 111 {
 112   int res = __getlogin_r_loginuid (name, namesize);
 113   if (res >= 0)
 114     return res;
 115
 116   return getlogin_r_fd0 (name, namesize);
 117 }
 118 libc_hidden_def (__getlogin_r)
 119 weak_alias (__getlogin_r, getlogin_r)
 120 libc_hidden_weak (getlogin_r)