1  /* Work around unlinkat bugs on Solaris 9 and Hurd.
       2  
       3     Copyright (C) 2009-2023 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 */