1 /* Define at-style functions like fstatat, unlinkat, fchownat, etc.
2    Copyright (C) 2006, 2009-2021 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
AT_FUNC_NAME(int fd,char const * file AT_FUNC_POST_FILE_PARAM_DECLS)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