lib/unlink.c

   1 /* Work around unlink bugs.
   2
   3    Copyright (C) 2009-2020 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 "filename.h"
  28
  29 #undef unlink
  30 #if defined _WIN32 && !defined __CYGWIN__
  31 # define unlink _unlink
  32 #endif
  33
  34 /* Remove file NAME.
  35    Return 0 if successful, -1 if not.  */
  36
  37 int
  38 rpl_unlink (char const *name)
  39 {
  40   /* Work around Solaris 9 bug where unlink("file/") succeeds.  */
  41   size_t len = strlen (name);
  42   int result = 0;
  43   if (len && ISSLASH (name[len - 1]))
  44     {
  45       /* We can't unlink(2) something if it doesn't exist.  If it does
  46          exist, then it resolved to a directory, due to the trailing
  47          slash, and POSIX requires that the unlink attempt to remove
  48          that directory (which would leave the symlink dangling).
  49          Unfortunately, Solaris 9 is one of the platforms where the
  50          root user can unlink directories, and we don't want to
  51          cripple this behavior on real directories, even if it is
  52          seldom needed (at any rate, it's nicer to let coreutils'
  53          unlink(1) give the correct errno for non-root users).  But we
  54          don't know whether name was an actual directory, or a symlink
  55          to a directory; and due to the bug of ignoring trailing
  56          slash, Solaris 9 would end up successfully unlinking the
  57          symlink instead of the directory.  Technically, we could use
  58          realpath to find the canonical directory name to attempt
  59          deletion on.  But that is a lot of work for a corner case; so
  60          we instead just use an lstat on the shortened name, and
  61          reject symlinks with trailing slashes.  The root user of
  62          unlink(1) will just have to live with the rule that they
  63          can't delete a directory via a symlink.  */
  64       struct stat st;
  65       result = lstat (name, &st);
  66       if (result == 0)
  67         {
  68           /* Trailing NUL will overwrite the trailing slash.  */
  69           char *short_name = malloc (len);
  70           if (!short_name)
  71             return -1;
  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 }