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      1 /* Define at-style functions like fstatat, unlinkat, fchownat, etc.
      2    Copyright (C) 2006, 2009-2022 Free Software Foundation, Inc.
      3 
      4    This program is free software: you can redistribute it and/or modify
      5    it under the terms of the GNU General Public License as published by
      6    the Free Software Foundation, either version 3 of the License, or
      7    (at your option) any later version.
      8 
      9    This program is distributed in the hope that it will be useful,
     10    but WITHOUT ANY WARRANTY; without even the implied warranty of
     11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
     12    GNU General Public License for more details.
     13 
     14    You should have received a copy of the GNU General Public License
     15    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
     16 
     17 /* written by Jim Meyering */
     18 
     19 #include "filename.h" /* solely for definition of IS_ABSOLUTE_FILE_NAME */
     20 
     21 #ifdef GNULIB_SUPPORT_ONLY_AT_FDCWD
     22 # include <errno.h>
     23 # ifndef ENOTSUP
     24 #  define ENOTSUP EINVAL
     25 # endif
     26 #else
     27 # include "openat.h"
     28 # include "openat-priv.h"
     29 # include "save-cwd.h"
     30 #endif
     31 
     32 #ifdef AT_FUNC_USE_F1_COND
     33 # define CALL_FUNC(F)                           \
     34   (flag == AT_FUNC_USE_F1_COND                  \
     35     ? AT_FUNC_F1 (F AT_FUNC_POST_FILE_ARGS)     \
     36     : AT_FUNC_F2 (F AT_FUNC_POST_FILE_ARGS))
     37 # define VALIDATE_FLAG(F)                       \
     38   if (flag & ~AT_FUNC_USE_F1_COND)              \
     39     {                                           \
     40       errno = EINVAL;                           \
     41       return FUNC_FAIL;                         \
     42     }
     43 #else
     44 # define CALL_FUNC(F) (AT_FUNC_F1 (F AT_FUNC_POST_FILE_ARGS))
     45 # define VALIDATE_FLAG(F) /* empty */
     46 #endif
     47 
     48 #ifdef AT_FUNC_RESULT
     49 # define FUNC_RESULT AT_FUNC_RESULT
     50 #else
     51 # define FUNC_RESULT int
     52 #endif
     53 
     54 #ifdef AT_FUNC_FAIL
     55 # define FUNC_FAIL AT_FUNC_FAIL
     56 #else
     57 # define FUNC_FAIL -1
     58 #endif
     59 
     60 /* Call AT_FUNC_F1 to operate on FILE, which is in the directory
     61    open on descriptor FD.  If AT_FUNC_USE_F1_COND is defined to a value,
     62    AT_FUNC_POST_FILE_PARAM_DECLS must include a parameter named flag;
     63    call AT_FUNC_F2 if FLAG is 0 or fail if FLAG contains more bits than
     64    AT_FUNC_USE_F1_COND.  Return int and fail with -1 unless AT_FUNC_RESULT
     65    or AT_FUNC_FAIL are defined.  If possible, do it without changing the
     66    working directory.  Otherwise, resort to using save_cwd/fchdir,
     67    then AT_FUNC_F?/restore_cwd.  If either the save_cwd or the restore_cwd
     68    fails, then give a diagnostic and exit nonzero.  */
     69 FUNC_RESULT
     70 AT_FUNC_NAME (int fd, char const *file AT_FUNC_POST_FILE_PARAM_DECLS)
     71 {
     72   VALIDATE_FLAG (flag);
     73 
     74   if (fd == AT_FDCWD || IS_ABSOLUTE_FILE_NAME (file))
     75     return CALL_FUNC (file);
     76 
     77 #ifdef GNULIB_SUPPORT_ONLY_AT_FDCWD
     78   errno = ENOTSUP;
     79   return FUNC_FAIL;
     80 #else
     81   {
     82   /* Be careful to choose names unlikely to conflict with
     83      AT_FUNC_POST_FILE_PARAM_DECLS.  */
     84   struct saved_cwd saved_cwd;
     85   int saved_errno;
     86   FUNC_RESULT err;
     87 
     88   {
     89     char proc_buf[OPENAT_BUFFER_SIZE];
     90     char *proc_file = openat_proc_name (proc_buf, fd, file);
     91     if (proc_file)
     92       {
     93         FUNC_RESULT proc_result = CALL_FUNC (proc_file);
     94         int proc_errno = errno;
     95         if (proc_file != proc_buf)
     96           free (proc_file);
     97         /* If the syscall succeeds, or if it fails with an unexpected
     98            errno value, then return right away.  Otherwise, fall through
     99            and resort to using save_cwd/restore_cwd.  */
    100         if (FUNC_FAIL != proc_result)
    101           return proc_result;
    102         if (! EXPECTED_ERRNO (proc_errno))
    103           {
    104             errno = proc_errno;
    105             return proc_result;
    106           }
    107       }
    108   }
    109 
    110   if (save_cwd (&saved_cwd) != 0)
    111     openat_save_fail (errno);
    112   if (0 <= fd && fd == saved_cwd.desc)
    113     {
    114       /* If saving the working directory collides with the user's
    115          requested fd, then the user's fd must have been closed to
    116          begin with.  */
    117       free_cwd (&saved_cwd);
    118       errno = EBADF;
    119       return FUNC_FAIL;
    120     }
    121 
    122   if (fchdir (fd) != 0)
    123     {
    124       saved_errno = errno;
    125       free_cwd (&saved_cwd);
    126       errno = saved_errno;
    127       return FUNC_FAIL;
    128     }
    129 
    130   err = CALL_FUNC (file);
    131   saved_errno = (err == FUNC_FAIL ? errno : 0);
    132 
    133   if (restore_cwd (&saved_cwd) != 0)
    134     openat_restore_fail (errno);
    135 
    136   free_cwd (&saved_cwd);
    137 
    138   if (saved_errno)
    139     errno = saved_errno;
    140   return err;
    141   }
    142 #endif
    143 }
    144 #undef CALL_FUNC
    145 #undef FUNC_RESULT
    146 #undef FUNC_FAIL
    147