lib/unlinkat.c

   1 /* Work around unlinkat bugs on Solaris 9 and Hurd.
   2
   3    Copyright (C) 2009-2024 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 /* Written by Eric Blake.  */
  19
  20 #include <config.h>
  21
  22 #include <unistd.h>
  23
  24 #include <errno.h>
  25 #include <fcntl.h>
  26 #include <string.h>
  27 #include <sys/stat.h>
  28
  29 #include <stdlib.h>
  30
  31 #include "filename.h"
  32 #include "openat.h"
  33
  34 #if HAVE_UNLINKAT
  35
  36 # undef unlinkat
  37
  38 /* unlinkat without AT_REMOVEDIR does not honor trailing / on Solaris 9.
  39    Hurd has the same issue.
  40
  41    unlinkat without AT_REMOVEDIR erroneously ignores ".." on Darwin 14.
  42
  43    Solve these in a similar manner to unlink.  */
  44
  45 int
  46 rpl_unlinkat (int fd, char const *name, int flag)
  47 {
  48   size_t len;
  49   int result = 0;
  50   /* rmdir behavior has no problems with trailing slash.  */
  51   if (flag & AT_REMOVEDIR)
  52     return unlinkat (fd, name, flag);
  53
  54   len = strlen (name);
  55   if (len && ISSLASH (name[len - 1]))
  56     {
  57       /* See the lengthy comment in unlink.c why we disobey the POSIX
  58          rule of letting unlink("link-to-dir/") attempt to unlink a
  59          directory.  */
  60       struct stat st;
  61       result = fstatat (fd, name, &st, AT_SYMLINK_NOFOLLOW);
  62       if (result == 0 || errno == EOVERFLOW)
  63         {
  64           /* Trailing NUL will overwrite the trailing slash.  */
  65           char *short_name = malloc (len);
  66           if (!short_name)
  67             {
  68               errno = EPERM;
  69               return -1;
  70             }
  71           memcpy (short_name, name, len);
  72           while (len && ISSLASH (short_name[len - 1]))
  73             short_name[--len] = '\0';
  74           if (len && (fstatat (fd, short_name, &st, AT_SYMLINK_NOFOLLOW)
  75                       || S_ISLNK (st.st_mode)))
  76             {
  77               free (short_name);
  78               errno = EPERM;
  79               return -1;
  80             }
  81           free (short_name);
  82           result = 0;
  83         }
  84     }
  85   if (!result)
  86     {
  87 # if UNLINK_PARENT_BUG
  88       if (len >= 2 && name[len - 1] == '.' && name[len - 2] == '.'
  89           && (len == 2 || ISSLASH (name[len - 3])))
  90         {
  91           errno = EISDIR; /* could also use EPERM */
  92           return -1;
  93         }
  94 # endif
  95       result = unlinkat (fd, name, flag);
  96     }
  97   return result;
  98 }
  99
 100 #else /* !HAVE_UNLINKAT */
 101
 102 /* Replacement for Solaris' function by the same name.
 103    <https://www.google.com/search?q=unlinkat+site:docs.oracle.com>
 104    First, try to simulate it via (unlink|rmdir) ("/proc/self/fd/FD/FILE").
 105    Failing that, simulate it via save_cwd/fchdir/(unlink|rmdir)/restore_cwd.
 106    If either the save_cwd or the restore_cwd fails (relatively unlikely),
 107    then give a diagnostic and exit nonzero.
 108    Otherwise, this function works just like Solaris' unlinkat.  */
 109
 110 # define AT_FUNC_NAME unlinkat
 111 # define AT_FUNC_F1 rmdir
 112 # define AT_FUNC_F2 unlink
 113 # define AT_FUNC_USE_F1_COND AT_REMOVEDIR
 114 # define AT_FUNC_POST_FILE_PARAM_DECLS , int flag
 115 # define AT_FUNC_POST_FILE_ARGS        /* empty */
 116 # include "at-func.c"
 117 # undef AT_FUNC_NAME
 118 # undef AT_FUNC_F1
 119 # undef AT_FUNC_F2
 120 # undef AT_FUNC_USE_F1_COND
 121 # undef AT_FUNC_POST_FILE_PARAM_DECLS
 122 # undef AT_FUNC_POST_FILE_ARGS
 123
 124 #endif /* !HAVE_UNLINKAT */