1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
|
/* Copyright (C) 1991-2023 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <errno.h>
#include <signal.h>
#include <stdlib.h>
#include <unistd.h>
#include <sigsetops.h>
#include <spawn.h>
#include <pthread.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <stdio.h>
#include <libc-lock.h>
#include <not-errno.h>
#include <not-cancel.h>
#include <internal-signals.h>
#define SHELL_PATH "/bin/sh" /* Path of the shell. */
#define SHELL_NAME "sh" /* Name to give it. */
/* This system implementation aims to be thread-safe, which requires to
restore the signal dispositions for SIGINT and SIGQUIT correctly and to
deal with cancellation by terminating the child process.
The signal disposition restoration on the single-thread case is
straighfoward. For multithreaded case, a reference-counter with a lock
is used, so the first thread will set the SIGINT/SIGQUIT dispositions and
last thread will restore them.
Cancellation handling is done with thread cancellation clean-up handlers
on waitpid call. */
#ifdef _LIBC_REENTRANT
static struct sigaction intr, quit;
static int sa_refcntr;
__libc_lock_define_initialized (static, lock);
# define DO_LOCK() __libc_lock_lock (lock)
# define DO_UNLOCK() __libc_lock_unlock (lock)
# define INIT_LOCK() ({ __libc_lock_init (lock); sa_refcntr = 0; })
# define ADD_REF() sa_refcntr++
# define SUB_REF() --sa_refcntr
#else
# define DO_LOCK()
# define DO_UNLOCK()
# define INIT_LOCK()
# define ADD_REF() 0
# define SUB_REF() 0
#endif
#if defined(_LIBC_REENTRANT) && defined(SIGCANCEL)
struct cancel_handler_args
{
struct sigaction *quit;
struct sigaction *intr;
pid_t pid;
};
static void
cancel_handler (void *arg)
{
struct cancel_handler_args *args = (struct cancel_handler_args *) (arg);
__kill_noerrno (args->pid, SIGKILL);
int state;
__pthread_setcancelstate (PTHREAD_CANCEL_DISABLE, &state);
TEMP_FAILURE_RETRY (__waitpid (args->pid, NULL, 0));
__pthread_setcancelstate (state, NULL);
DO_LOCK ();
if (SUB_REF () == 0)
{
__sigaction (SIGQUIT, args->quit, NULL);
__sigaction (SIGINT, args->intr, NULL);
}
DO_UNLOCK ();
}
#endif
/* Execute LINE as a shell command, returning its status. */
static int
do_system (const char *line)
{
int status = -1;
int ret;
pid_t pid;
struct sigaction sa;
#ifndef _LIBC_REENTRANT
struct sigaction intr, quit;
#endif
sigset_t omask;
sigset_t reset;
sa.sa_handler = SIG_IGN;
sa.sa_flags = 0;
__sigemptyset (&sa.sa_mask);
DO_LOCK ();
if (ADD_REF () == 0)
{
/* sigaction can not fail with SIGINT/SIGQUIT used with SIG_IGN. */
__sigaction (SIGINT, &sa, &intr);
__sigaction (SIGQUIT, &sa, &quit);
}
DO_UNLOCK ();
__sigaddset (&sa.sa_mask, SIGCHLD);
/* sigprocmask can not fail with SIG_BLOCK used with valid input
arguments. */
__sigprocmask (SIG_BLOCK, &sa.sa_mask, &omask);
__sigemptyset (&reset);
if (intr.sa_handler != SIG_IGN)
__sigaddset(&reset, SIGINT);
if (quit.sa_handler != SIG_IGN)
__sigaddset(&reset, SIGQUIT);
posix_spawnattr_t spawn_attr;
/* None of the posix_spawnattr_* function returns an error, including
posix_spawnattr_setflags for the follow specific usage (using valid
flags). */
__posix_spawnattr_init (&spawn_attr);
__posix_spawnattr_setsigmask (&spawn_attr, &omask);
__posix_spawnattr_setsigdefault (&spawn_attr, &reset);
__posix_spawnattr_setflags (&spawn_attr,
POSIX_SPAWN_SETSIGDEF | POSIX_SPAWN_SETSIGMASK);
ret = __posix_spawn (&pid, SHELL_PATH, 0, &spawn_attr,
(char *const[]){ (char *) SHELL_NAME,
(char *) "-c",
(char *) "--",
(char *) line, NULL },
__environ);
__posix_spawnattr_destroy (&spawn_attr);
if (ret == 0)
{
/* Cancellation results in cleanup handlers running as exceptions in
the block where they were installed, so it is safe to reference
stack variable allocate in the broader scope. */
#if defined(_LIBC_REENTRANT) && defined(SIGCANCEL)
struct cancel_handler_args cancel_args =
{
.quit = &quit,
.intr = &intr,
.pid = pid
};
__libc_cleanup_region_start (1, cancel_handler, &cancel_args);
#endif
/* Note the system() is a cancellation point. But since we call
waitpid() which itself is a cancellation point we do not
have to do anything here. */
if (TEMP_FAILURE_RETRY (__waitpid (pid, &status, 0)) != pid)
status = -1;
#if defined(_LIBC_REENTRANT) && defined(SIGCANCEL)
__libc_cleanup_region_end (0);
#endif
}
else
/* POSIX states that failure to execute the shell should return
as if the shell had terminated using _exit(127). */
status = W_EXITCODE (127, 0);
/* sigaction can not fail with SIGINT/SIGQUIT used with old
disposition. Same applies for sigprocmask. */
DO_LOCK ();
if (SUB_REF () == 0)
{
__sigaction (SIGINT, &intr, NULL);
__sigaction (SIGQUIT, &quit, NULL);
}
DO_UNLOCK ();
__sigprocmask (SIG_SETMASK, &omask, NULL);
if (ret != 0)
__set_errno (ret);
return status;
}
int
__libc_system (const char *line)
{
if (line == NULL)
/* Check that we have a command processor available. It might
not be available after a chroot(), for example. */
return do_system ("exit 0") == 0;
return do_system (line);
}
weak_alias (__libc_system, system)
|
