lib/unlink.c

   1 /* Work around unlink bugs.
   2
   3    Copyright (C) 2009-2019 Free Software Foundation, Inc.
   4
   5    This program is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 3 of the License, or
   8    (at your option) any later version.
   9
  10    This program 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
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  17
  18 #include <config.h>
  19
  20 #include <unistd.h>
  21
  22 #include <errno.h>
  23 #include <stdlib.h>
  24 #include <string.h>
  25 #include <sys/stat.h>
  26
  27 #include "dosname.h"
  28
  29 #undef unlink
  30
  31 /* Remove file NAME.
  32    Return 0 if successful, -1 if not.  */
  33
  34 int
  35 rpl_unlink (char const *name)
  36 {
  37   /* Work around Solaris 9 bug where unlink("file/") succeeds.  */
  38   size_t len = strlen (name);
  39   int result = 0;
  40   if (len && ISSLASH (name[len - 1]))
  41     {
  42       /* We can't unlink(2) something if it doesn't exist.  If it does
  43          exist, then it resolved to a directory, due to the trailing
  44          slash, and POSIX requires that the unlink attempt to remove
  45          that directory (which would leave the symlink dangling).
  46          Unfortunately, Solaris 9 is one of the platforms where the
  47          root user can unlink directories, and we don't want to
  48          cripple this behavior on real directories, even if it is
  49          seldom needed (at any rate, it's nicer to let coreutils'
  50          unlink(1) give the correct errno for non-root users).  But we
  51          don't know whether name was an actual directory, or a symlink
  52          to a directory; and due to the bug of ignoring trailing
  53          slash, Solaris 9 would end up successfully unlinking the
  54          symlink instead of the directory.  Technically, we could use
  55          realpath to find the canonical directory name to attempt
  56          deletion on.  But that is a lot of work for a corner case; so
  57          we instead just use an lstat on the shortened name, and
  58          reject symlinks with trailing slashes.  The root user of
  59          unlink(1) will just have to live with the rule that they
  60          can't delete a directory via a symlink.  */
  61       struct stat st;
  62       result = lstat (name, &st);
  63       if (result == 0)
  64         {
  65           /* Trailing NUL will overwrite the trailing slash.  */
  66           char *short_name = malloc (len);
  67           if (!short_name)
  68             {
  69               errno = EPERM;
  70               return -1;
  71             }
  72           memcpy (short_name, name, len);
  73           while (len && ISSLASH (short_name[len - 1]))
  74             short_name[--len] = '\0';
  75           if (len && (lstat (short_name, &st) || S_ISLNK (st.st_mode)))
  76             {
  77               free (short_name);
  78               errno = EPERM;
  79               return -1;
  80             }
  81           free (short_name);
  82         }
  83     }
  84   if (!result)
  85     {
  86 #if UNLINK_PARENT_BUG
  87       if (len >= 2 && name[len - 1] == '.' && name[len - 2] == '.'
  88           && (len == 2 || ISSLASH (name[len - 3])))
  89         {
  90           errno = EISDIR; /* could also use EPERM */
  91           return -1;
  92         }
  93 #endif
  94       result = unlink (name);
  95     }
  96   return result;
  97 }