misc/mntent_r.c

   1 /* Utilities for reading/writing fstab, mtab, etc.
   2    Copyright (C) 1995-2019 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <alloca.h>
  20 #include <mntent.h>
  21 #include <stdbool.h>
  22 #include <stdio.h>
  23 #include <stdio_ext.h>
  24 #include <string.h>
  25 #include <sys/types.h>
  26
  27 #define flockfile(s) _IO_flockfile (s)
  28 #define funlockfile(s) _IO_funlockfile (s)
  29
  30 #undef __setmntent
  31 #undef __endmntent
  32 #undef __getmntent_r
  33
  34 /* Prepare to begin reading and/or writing mount table entries from the
  35    beginning of FILE.  MODE is as for `fopen'.  */
  36 FILE *
  37 __setmntent (const char *file, const char *mode)
  38 {
  39   /* Extend the mode parameter with "c" to disable cancellation in the
  40      I/O functions and "e" to set FD_CLOEXEC.  */
  41   size_t modelen = strlen (mode);
  42   char newmode[modelen + 3];
  43   memcpy (mempcpy (newmode, mode, modelen), "ce", 3);
  44   FILE *result = fopen (file, newmode);
  45
  46   if (result != NULL)
  47     /* We do the locking ourselves.  */
  48     __fsetlocking (result, FSETLOCKING_BYCALLER);
  49
  50   return result;
  51 }
  52 libc_hidden_def (__setmntent)
  53 weak_alias (__setmntent, setmntent)
  54
  55
  56 /* Close a stream opened with `setmntent'.  */
  57 int
  58 __endmntent (FILE *stream)
  59 {
  60   if (stream)           /* SunOS 4.x allows for NULL stream */
  61     fclose (stream);
  62   return 1;             /* SunOS 4.x says to always return 1 */
  63 }
  64 libc_hidden_def (__endmntent)
  65 weak_alias (__endmntent, endmntent)
  66
  67
  68 /* Since the values in a line are separated by spaces, a name cannot
  69    contain a space.  Therefore some programs encode spaces in names
  70    by the strings "\040".  We undo the encoding when reading an entry.
  71    The decoding happens in place.  */
  72 static char *
  73 decode_name (char *buf)
  74 {
  75   char *rp = buf;
  76   char *wp = buf;
  77
  78   do
  79     if (rp[0] == '\\' && rp[1] == '0' && rp[2] == '4' && rp[3] == '0')
  80       {
  81         /* \040 is a SPACE.  */
  82         *wp++ = ' ';
  83         rp += 3;
  84       }
  85     else if (rp[0] == '\\' && rp[1] == '0' && rp[2] == '1' && rp[3] == '1')
  86       {
  87         /* \011 is a TAB.  */
  88         *wp++ = '\t';
  89         rp += 3;
  90       }
  91     else if (rp[0] == '\\' && rp[1] == '0' && rp[2] == '1' && rp[3] == '2')
  92       {
  93         /* \012 is a NEWLINE.  */
  94         *wp++ = '\n';
  95         rp += 3;
  96       }
  97     else if (rp[0] == '\\' && rp[1] == '\\')
  98       {
  99         /* We have to escape \\ to be able to represent all characters.  */
 100         *wp++ = '\\';
 101         rp += 1;
 102       }
 103     else if (rp[0] == '\\' && rp[1] == '1' && rp[2] == '3' && rp[3] == '4')
 104       {
 105         /* \134 is also \\.  */
 106         *wp++ = '\\';
 107         rp += 3;
 108       }
 109     else
 110       *wp++ = *rp;
 111   while (*rp++ != '\0');
 112
 113   return buf;
 114 }
 115
 116 static bool
 117 get_mnt_entry (FILE *stream, struct mntent *mp, char *buffer, int bufsiz)
 118 {
 119   char *cp;
 120   char *head;
 121
 122   do
 123     {
 124       char *end_ptr;
 125
 126       if (__fgets_unlocked (buffer, bufsiz, stream) == NULL)
 127           return false;
 128
 129       end_ptr = strchr (buffer, '\n');
 130       if (end_ptr != NULL)      /* chop newline */
 131         {
 132           /* Do not walk past the start of buffer if it's all whitespace.  */
 133           while (end_ptr != buffer
 134                  && (end_ptr[-1] == ' ' || end_ptr[-1] == '\t'))
 135             end_ptr--;
 136           *end_ptr = '\0';
 137         }
 138       else
 139         {
 140           /* Not the whole line was read.  Do it now but forget it.  */
 141           char tmp[1024];
 142           while (__fgets_unlocked (tmp, sizeof tmp, stream) != NULL)
 143             if (strchr (tmp, '\n') != NULL)
 144               break;
 145         }
 146
 147       head = buffer + strspn (buffer, " \t");
 148       /* skip empty lines and comment lines:  */
 149     }
 150   while (head[0] == '\0' || head[0] == '#');
 151
 152   cp = __strsep (&head, " \t");
 153   mp->mnt_fsname = cp != NULL ? decode_name (cp) : (char *) "";
 154   if (head)
 155     head += strspn (head, " \t");
 156   cp = __strsep (&head, " \t");
 157   mp->mnt_dir = cp != NULL ? decode_name (cp) : (char *) "";
 158   if (head)
 159     head += strspn (head, " \t");
 160   cp = __strsep (&head, " \t");
 161   mp->mnt_type = cp != NULL ? decode_name (cp) : (char *) "";
 162   if (head)
 163     head += strspn (head, " \t");
 164   cp = __strsep (&head, " \t");
 165   mp->mnt_opts = cp != NULL ? decode_name (cp) : (char *) "";
 166   switch (head ? sscanf (head, " %d %d ", &mp->mnt_freq, &mp->mnt_passno) : 0)
 167     {
 168     case 0:
 169       mp->mnt_freq = 0;
 170       /* Fall through.  */
 171     case 1:
 172       mp->mnt_passno = 0;
 173       /* Fall through.  */
 174     case 2:
 175       break;
 176     }
 177
 178   return true;
 179 }
 180
 181 /* Read one mount table entry from STREAM.  Returns a pointer to storage
 182    reused on the next call, or null for EOF or error (use feof/ferror to
 183    check).  */
 184 struct mntent *
 185 __getmntent_r (FILE *stream, struct mntent *mp, char *buffer, int bufsiz)
 186 {
 187   struct mntent *result;
 188
 189   flockfile (stream);
 190   while (true)
 191     if (get_mnt_entry (stream, mp, buffer, bufsiz))
 192       {
 193         /* If the file system is autofs look for a mount option hint
 194            ("ignore") to skip the entry.  */
 195         if (strcmp (mp->mnt_type, "autofs") == 0 && __hasmntopt (mp, "ignore"))
 196           memset (mp, 0, sizeof (*mp));
 197         else
 198           {
 199             result = mp;
 200             break;
 201           }
 202       }
 203     else
 204       {
 205         result = NULL;
 206         break;
 207       }
 208   funlockfile (stream);
 209
 210   return result;
 211 }
 212 libc_hidden_def (__getmntent_r)
 213 weak_alias (__getmntent_r, getmntent_r)
 214
 215
 216 /* We have to use an encoding for names if they contain spaces or tabs.
 217    To be able to represent all characters we also have to escape the
 218    backslash itself.  This "function" must be a macro since we use
 219    `alloca'.  */
 220 #define encode_name(name) \
 221   do {                                                                        \
 222     const char *rp = name;                                                    \
 223                                                                               \
 224     while (*rp != '\0')                                                       \
 225       if (*rp == ' ' || *rp == '\t' || *rp == '\n' || *rp == '\\')            \
 226         break;                                                                \
 227       else                                                                    \
 228         ++rp;                                                                 \
 229                                                                               \
 230     if (*rp != '\0')                                                          \
 231       {                                                                       \
 232         /* In the worst case the length of the string can increase to         \
 233            four times the current length.  */                                 \
 234         char *wp;                                                             \
 235                                                                               \
 236         rp = name;                                                            \
 237         name = wp = (char *) alloca (strlen (name) * 4 + 1);                  \
 238                                                                               \
 239         do                                                                    \
 240           if (*rp == ' ')                                                     \
 241             {                                                                 \
 242               *wp++ = '\\';                                                   \
 243               *wp++ = '0';                                                    \
 244               *wp++ = '4';                                                    \
 245               *wp++ = '0';                                                    \
 246             }                                                                 \
 247           else if (*rp == '\t')                                               \
 248             {                                                                 \
 249               *wp++ = '\\';                                                   \
 250               *wp++ = '0';                                                    \
 251               *wp++ = '1';                                                    \
 252               *wp++ = '1';                                                    \
 253             }                                                                 \
 254           else if (*rp == '\n')                                               \
 255             {                                                                 \
 256               *wp++ = '\\';                                                   \
 257               *wp++ = '0';                                                    \
 258               *wp++ = '1';                                                    \
 259               *wp++ = '2';                                                    \
 260             }                                                                 \
 261           else if (*rp == '\\')                                               \
 262             {                                                                 \
 263               *wp++ = '\\';                                                   \
 264               *wp++ = '\\';                                                   \
 265             }                                                                 \
 266           else                                                                \
 267             *wp++ = *rp;                                                      \
 268         while (*rp++ != '\0');                                                \
 269       }                                                                       \
 270   } while (0)
 271
 272
 273 /* Write the mount table entry described by MNT to STREAM.
 274    Return zero on success, nonzero on failure.  */
 275 int
 276 __addmntent (FILE *stream, const struct mntent *mnt)
 277 {
 278   struct mntent mntcopy = *mnt;
 279   if (fseek (stream, 0, SEEK_END))
 280     return 1;
 281
 282   /* Encode spaces and tabs in the names.  */
 283   encode_name (mntcopy.mnt_fsname);
 284   encode_name (mntcopy.mnt_dir);
 285   encode_name (mntcopy.mnt_type);
 286   encode_name (mntcopy.mnt_opts);
 287
 288   return (fprintf (stream, "%s %s %s %s %d %d\n",
 289                    mntcopy.mnt_fsname,
 290                    mntcopy.mnt_dir,
 291                    mntcopy.mnt_type,
 292                    mntcopy.mnt_opts,
 293                    mntcopy.mnt_freq,
 294                    mntcopy.mnt_passno) < 0
 295           || fflush (stream) != 0);
 296 }
 297 weak_alias (__addmntent, addmntent)
 298
 299
 300 /* Search MNT->mnt_opts for an option matching OPT.
 301    Returns the address of the substring, or null if none found.  */
 302 char *
 303 __hasmntopt (const struct mntent *mnt, const char *opt)
 304 {
 305   const size_t optlen = strlen (opt);
 306   char *rest = mnt->mnt_opts, *p;
 307
 308   while ((p = strstr (rest, opt)) != NULL)
 309     {
 310       if ((p == rest || p[-1] == ',')
 311           && (p[optlen] == '\0' || p[optlen] == '=' || p[optlen] == ','))
 312         return p;
 313
 314       rest = strchr (p, ',');
 315       if (rest == NULL)
 316         break;
 317       ++rest;
 318     }
 319
 320   return NULL;
 321 }
 322 libc_hidden_def (__hasmntopt)
 323 weak_alias (__hasmntopt, hasmntopt)