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freopen-safer.c

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1/* Invoke freopen, but avoid some glitches.-
2-
3 Copyright (C) 2009-2018 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 "stdio-safer.h"-
23-
24#include <errno.h>-
25#include <fcntl.h>-
26#include <stdbool.h>-
27#include <unistd.h>-
28-
29#ifndef FALLTHROUGH-
30# if __GNUC__ < 7-
31# define FALLTHROUGH ((void) 0)-
32# else-
33# define FALLTHROUGH __attribute__ ((__fallthrough__))-
34# endif-
35#endif-
36-
37/* Guarantee that FD is open; all smaller FDs must already be open.-
38 Return true if successful. */-
39static bool-
40protect_fd (int fd)-
41{-
42 int value = open ("/dev/null", O_RDONLY);-
43 if (value != fd)
value != fdDescription
TRUEnever evaluated
FALSEnever evaluated
0
44 {-
45 if (0 <= value)
0 <= valueDescription
TRUEnever evaluated
FALSEnever evaluated
0
46 {-
47 close (value);-
48 errno = EBADF; /* Unexpected; this is as good as anything else. */-
49 }
never executed: end of block
0
50 return false;
never executed: return 0 ;
0
51 }-
52 return true;
never executed: return 1 ;
0
53}-
54-
55/* Like freopen, but guarantee that reopening stdin, stdout, or stderr-
56 preserves the invariant that STDxxx_FILENO==fileno(stdxxx), and-
57 that no other stream will interfere with the standard streams.-
58 This is necessary because most freopen implementations will change-
59 the associated fd of a stream to the lowest available slot. */-
60-
61FILE *-
62freopen_safer (char const *name, char const *mode, FILE *f)-
63{-
64 /* Unfortunately, we cannot use the fopen_safer approach of using-
65 fdopen (dup_safer (fileno (freopen (cmd, mode, f)))), because we-
66 need to return f itself. The implementation of freopen(NULL,m,f)-
67 is system-dependent, so the best we can do is guarantee that all-
68 lower-valued standard fds are open prior to the freopen call,-
69 even though this puts more pressure on open fds. */-
70 bool protect_in = false;-
71 bool protect_out = false;-
72 bool protect_err = false;-
73 int saved_errno;-
74-
75 switch (fileno (f))-
76 {-
77 default: /* -1 or not a standard stream. */
never executed: default:
0
78 if (dup2 (STDERR_FILENO, STDERR_FILENO) != STDERR_FILENO)
dup2 ( 2 , 2 ) != 2Description
TRUEnever evaluated
FALSEnever evaluated
0
79 protect_err = true;
never executed: protect_err = 1 ;
0
80 FALLTHROUGH;-
81 case STDERR_FILENO:
code before this statement never executed: case 2 :
never executed: case 2 :
0
82 if (dup2 (STDOUT_FILENO, STDOUT_FILENO) != STDOUT_FILENO)
dup2 ( 1 , 1 ) != 1Description
TRUEnever evaluated
FALSEnever evaluated
0
83 protect_out = true;
never executed: protect_out = 1 ;
0
84 FALLTHROUGH;-
85 case STDOUT_FILENO:
code before this statement never executed: case 1 :
never executed: case 1 :
0
86 if (dup2 (STDIN_FILENO, STDIN_FILENO) != STDIN_FILENO)
dup2 ( 0 , 0 ) != 0Description
TRUEnever evaluated
FALSEnever evaluated
0
87 protect_in = true;
never executed: protect_in = 1 ;
0
88 FALLTHROUGH;-
89 case STDIN_FILENO:
code before this statement never executed: case 0 :
executed 181 times by 5 tests: case 0 :
Executed by:
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0-181
90 /* Nothing left to protect. */-
91 break;
executed 181 times by 5 tests: break;
Executed by:
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181
92 }-
93 if (protect_in && !protect_fd (STDIN_FILENO))
protect_inDescription
TRUEnever evaluated
FALSEevaluated 181 times by 5 tests
Evaluated by:
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!protect_fd ( 0 )Description
TRUEnever evaluated
FALSEnever evaluated
0-181
94 f = NULL;
never executed: f = ((void *)0) ;
0
95 else if (protect_out && !protect_fd (STDOUT_FILENO))
protect_outDescription
TRUEnever evaluated
FALSEevaluated 181 times by 5 tests
Evaluated by:
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!protect_fd ( 1 )Description
TRUEnever evaluated
FALSEnever evaluated
0-181
96 f = NULL;
never executed: f = ((void *)0) ;
0
97 else if (protect_err && !protect_fd (STDERR_FILENO))
protect_errDescription
TRUEnever evaluated
FALSEevaluated 181 times by 5 tests
Evaluated by:
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!protect_fd ( 2 )Description
TRUEnever evaluated
FALSEnever evaluated
0-181
98 f = NULL;
never executed: f = ((void *)0) ;
0
99 else-
100 f = freopen (name, mode, f);
executed 181 times by 5 tests: f = rpl_freopen (name, mode, f);
Executed by:
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181
101 saved_errno = errno;-
102 if (protect_err)
protect_errDescription
TRUEnever evaluated
FALSEevaluated 181 times by 5 tests
Evaluated by:
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0-181
103 close (STDERR_FILENO);
never executed: close ( 2 );
0
104 if (protect_out)
protect_outDescription
TRUEnever evaluated
FALSEevaluated 181 times by 5 tests
Evaluated by:
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0-181
105 close (STDOUT_FILENO);
never executed: close ( 1 );
0
106 if (protect_in)
protect_inDescription
TRUEnever evaluated
FALSEevaluated 181 times by 5 tests
Evaluated by:
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0-181
107 close (STDIN_FILENO);
never executed: close ( 0 );
0
108 if (!f)
!fDescription
TRUEevaluated 2 times by 2 tests
Evaluated by:
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FALSEevaluated 179 times by 5 tests
Evaluated by:
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2-179
109 errno = saved_errno;
executed 2 times by 2 tests: (*__errno_location ()) = saved_errno;
Executed by:
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2
110 return f;
executed 181 times by 5 tests: return f;
Executed by:
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181
111}-
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