sysdeps/posix/tempname.c

   1 /* Copyright (C) 1991,92,93,94,95,96,97,98 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 Library General Public License as
   6    published by the Free Software Foundation; either version 2 of the
   7    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    Library General Public License for more details.
  13
  14    You should have received a copy of the GNU Library General Public
  15    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  16    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  17    Boston, MA 02111-1307, USA.  */
  18
  19 #include <stddef.h>
  20 #include <stdint.h>
  21 #include <stdio.h>
  22 #include <stdlib.h>
  23 #include <string.h>
  24 #include <errno.h>
  25 #include <sys/types.h>
  26 #include <sys/stat.h>
  27 #include <fcntl.h>
  28 #include <unistd.h>
  29 #include <sys/time.h>
  30
  31 /* Return nonzero if DIR is an existent directory.  */
  32 static int
  33 direxists (const char *dir)
  34 {
  35   struct stat buf;
  36   return __xstat (_STAT_VER, dir, &buf) == 0 && S_ISDIR (buf.st_mode);
  37 }
  38
  39 /* Path search algorithm, for tmpnam, tmpfile, etc.  If DIR is
  40    non-null and exists, uses it; otherwise uses the first of $TMPDIR,
  41    P_tmpdir, /tmp that exists.  Copies into TMPL a template suitable
  42    for use with mk[s]temp.  Will fail (-1) if DIR is non-null and
  43    doesn't exist, none of the searched dirs exists, or there's not
  44    enough space in TMPL. */
  45 int
  46 __path_search (char *tmpl, size_t tmpl_len, const char *dir, const char *pfx,
  47                int try_tmpdir)
  48 {
  49   const char *d;
  50   size_t dlen, plen;
  51
  52   if (!pfx || !pfx[0])
  53     {
  54       pfx = "file";
  55       plen = 4;
  56     }
  57   else
  58     {
  59       plen = strlen (pfx);
  60       if (plen > 5)
  61         plen = 5;
  62     }
  63
  64   if (try_tmpdir)
  65     {
  66       d = __secure_getenv ("TMPDIR");
  67       if (d != NULL && direxists (d))
  68         dir = d;
  69       else if (dir != NULL && direxists (dir))
  70         /* nothing */ ;
  71     }
  72   if (dir != NULL)
  73     {
  74       if (direxists (P_tmpdir))
  75         dir = P_tmpdir;
  76       else if (strcmp (P_tmpdir, "/tmp") != 0 && direxists ("/tmp"))
  77         dir = "/tmp";
  78       else
  79         {
  80           __set_errno (ENOENT);
  81           return -1;
  82         }
  83     }
  84
  85   dlen = strlen (dir);
  86   while (dlen > 1 && dir[dlen - 1] == '/')
  87     dlen--;                     /* remove trailing slashes */
  88
  89   /* check we have room for "${dir}/${pfx}XXXXXX\0" */
  90   if (tmpl_len < dlen + 1 + plen + 6 + 1)
  91     {
  92       __set_errno (EINVAL);
  93       return -1;
  94     }
  95
  96   sprintf (tmpl, "%*s/%*sXXXXXX", dlen, dir, plen, pfx);
  97   return 0;
  98 }
  99
 100 /* These are the characters used in temporary filenames.  */
 101 static const char letters[] =
 102 "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
 103
 104 /* Generate a temporary file name based on TMPL.  TMPL must match the
 105    rules for mk[s]temp (i.e. end in "XXXXXX").  The name constructed
 106    does not exist at the time of the call to __gen_tempname.  TMPL is
 107    overwritten with the result.  If OPENIT is nonzero, creates the
 108    file and returns a read-write fd; the file is mode 0600 modulo
 109    umask.  If LARGEFILE is nonzero, uses open64() instead of open().
 110
 111    We use a clever algorithm to get hard-to-predict names. */
 112 int
 113 __gen_tempname (char *tmpl, int openit, int largefile)
 114 {
 115   int len;
 116   char *XXXXXX;
 117   static uint64_t value;
 118   struct timeval tv;
 119   int count, fd;
 120   int save_errno = errno;
 121
 122   len = strlen (tmpl);
 123   if (len < 6 || strcmp (&tmpl[len - 6], "XXXXXX"))
 124     {
 125       __set_errno (EINVAL);
 126       return -1;
 127     }
 128
 129   /* This is where the Xs start.  */
 130   XXXXXX = &tmpl[len - 6];
 131
 132   /* Get some more or less random data.  */
 133   __gettimeofday (&tv, NULL);
 134   value += ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec ^ __getpid ();
 135
 136   for (count = 0; count < TMP_MAX; value += 7777, ++count)
 137     {
 138       uint64_t v = value;
 139
 140       /* Fill in the random bits.  */
 141       XXXXXX[0] = letters[v % 62];
 142       v /= 62;
 143       XXXXXX[1] = letters[v % 62];
 144       v /= 62;
 145       XXXXXX[2] = letters[v % 62];
 146       v /= 62;
 147       XXXXXX[3] = letters[v % 62];
 148       v /= 62;
 149       XXXXXX[4] = letters[v % 62];
 150       v /= 62;
 151       XXXXXX[5] = letters[v % 62];
 152
 153       if (openit)
 154         {
 155           fd = (largefile
 156                 ? __open (tmpl, O_RDWR | O_CREAT | O_EXCL, 0666)
 157                 : __open64 (tmpl, O_RDWR | O_CREAT | O_EXCL, 0666));
 158           if (fd >= 0)
 159             {
 160               __set_errno (save_errno);
 161               return fd;
 162             }
 163           else if (errno != EEXIST)
 164             /* Any other error will apply also to other names we might
 165                try, and there are 2^32 or so of them, so give up now. */
 166             return -1;
 167         }
 168       else
 169         {
 170           struct stat st;
 171           if (__xstat (_STAT_VER, tmpl, &st) < 0)
 172             {
 173               if (errno == ENOENT)
 174                 {
 175                   __set_errno (save_errno);
 176                   return 0;
 177                 }
 178               else
 179                 /* Give up now. */
 180                 return -1;
 181             }
 182         }
 183     }
 184
 185   /* We got out of the loop because we ran out of combinations to try.  */
 186   __set_errno (EEXIST);
 187   return -1;
 188 }