1/* Copyright (C) 1991-2019 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
3
4 The GNU C Library is free software; you can redistribute it and/or
5 modify it under the terms of the GNU Lesser General Public
6 License as published by the Free Software Foundation; either
7 version 2.1 of the License, or (at your option) any later version.
8
9 The GNU C Library 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 GNU
12 Lesser General Public License for more details.
13
14 You should have received a copy of the GNU Lesser General Public
15 License along with the GNU C Library; if not, see
16 <http://www.gnu.org/licenses/>. */
17
18#include <errno.h>
19#include <signal.h>
20#include <stdlib.h>
21#include <unistd.h>
22#include <sigsetops.h>
23#include <spawn.h>
24#include <pthread.h>
25#include <sys/types.h>
26#include <sys/wait.h>
27#include <stdio.h>
28
29#include <libc-lock.h>
30#include <not-errno.h>
31#include <not-cancel.h>
32#include <internal-signals.h>
33
34#define SHELL_PATH "/bin/sh" /* Path of the shell. */
35#define SHELL_NAME "sh" /* Name to give it. */
36
37
38/* This system implementation aims to be thread-safe, which requires to
39 restore the signal dispositions for SIGINT and SIGQUIT correctly and to
40 deal with cancellation by terminating the child process.
41
42 The signal disposition restoration on the single-thread case is
43 straighfoward. For multithreaded case, a reference-counter with a lock
44 is used, so the first thread will set the SIGINT/SIGQUIT dispositions and
45 last thread will restore them.
46
47 Cancellation handling is done with thread cancellation clean-up handlers
48 on waitpid call. */
49
50#ifdef _LIBC_REENTRANT
51static struct sigaction intr, quit;
52static int sa_refcntr;
53__libc_lock_define_initialized (static, lock);
54
55# define DO_LOCK() __libc_lock_lock (lock)
56# define DO_UNLOCK() __libc_lock_unlock (lock)
57# define INIT_LOCK() ({ __libc_lock_init (lock); sa_refcntr = 0; })
58# define ADD_REF() sa_refcntr++
59# define SUB_REF() --sa_refcntr
60#else
61# define DO_LOCK()
62# define DO_UNLOCK()
63# define INIT_LOCK()
64# define ADD_REF() 0
65# define SUB_REF() 0
66#endif
67
68
69#if defined(_LIBC_REENTRANT) && defined(SIGCANCEL)
70struct cancel_handler_args
71{
72 struct sigaction *quit;
73 struct sigaction *intr;
74 pid_t pid;
75};
76
77static void
78cancel_handler (void *arg)
79{
80 struct cancel_handler_args *args = (struct cancel_handler_args *) (arg);
81
82 __kill_noerrno (args->pid, SIGKILL);
83
84 TEMP_FAILURE_RETRY (__waitpid_nocancel (args->pid, NULL, 0));
85
86 DO_LOCK ();
87 if (SUB_REF () == 0)
88 {
89 __sigaction (SIGQUIT, args->quit, NULL);
90 __sigaction (SIGINT, args->intr, NULL);
91 }
92 DO_UNLOCK ();
93}
94#endif
95
96/* Execute LINE as a shell command, returning its status. */
97static int
98do_system (const char *line)
99{
100 int status;
101 pid_t pid;
102 struct sigaction sa;
103#ifndef _LIBC_REENTRANT
104 struct sigaction intr, quit;
105#endif
106 sigset_t omask;
107 sigset_t reset;
108
109 sa.sa_handler = SIG_IGN;
110 sa.sa_flags = 0;
111 __sigemptyset (&sa.sa_mask);
112
113 DO_LOCK ();
114 if (ADD_REF () == 0)
115 {
116 /* sigaction can not fail with SIGINT/SIGQUIT used with SIG_IGN. */
117 __sigaction (SIGINT, &sa, &intr);
118 __sigaction (SIGQUIT, &sa, &quit);
119 }
120 DO_UNLOCK ();
121
122 __sigaddset (&sa.sa_mask, SIGCHLD);
123 /* sigprocmask can not fail with SIG_BLOCK used with valid input
124 arguments. */
125 __sigprocmask (SIG_BLOCK, &sa.sa_mask, &omask);
126
127 __sigemptyset (&reset);
128 if (intr.sa_handler != SIG_IGN)
129 __sigaddset(&reset, SIGINT);
130 if (quit.sa_handler != SIG_IGN)
131 __sigaddset(&reset, SIGQUIT);
132
133 posix_spawnattr_t spawn_attr;
134 /* None of the posix_spawnattr_* function returns an error, including
135 posix_spawnattr_setflags for the follow specific usage (using valid
136 flags). */
137 __posix_spawnattr_init (&spawn_attr);
138 __posix_spawnattr_setsigmask (&spawn_attr, &omask);
139 __posix_spawnattr_setsigdefault (&spawn_attr, &reset);
140 __posix_spawnattr_setflags (&spawn_attr,
141 POSIX_SPAWN_SETSIGDEF | POSIX_SPAWN_SETSIGMASK);
142
143 status = __posix_spawn (&pid, SHELL_PATH, 0, &spawn_attr,
144 (char *const[]){ (char*) SHELL_NAME,
145 (char*) "-c",
146 (char *) line, NULL },
147 __environ);
148 __posix_spawnattr_destroy (&spawn_attr);
149
150 if (status == 0)
151 {
152 /* Cancellation results in cleanup handlers running as exceptions in
153 the block where they were installed, so it is safe to reference
154 stack variable allocate in the broader scope. */
155#if defined(_LIBC_REENTRANT) && defined(SIGCANCEL)
156 struct cancel_handler_args cancel_args =
157 {
158 .quit = &quit,
159 .intr = &intr,
160 .pid = pid
161 };
162 __libc_cleanup_region_start (1, cancel_handler, &cancel_args);
163#endif
164 /* Note the system() is a cancellation point. But since we call
165 waitpid() which itself is a cancellation point we do not
166 have to do anything here. */
167 if (TEMP_FAILURE_RETRY (__waitpid (pid, &status, 0)) != pid)
168 status = -1;
169#if defined(_LIBC_REENTRANT) && defined(SIGCANCEL)
170 __libc_cleanup_region_end (0);
171#endif
172 }
173
174 DO_LOCK ();
175 if (SUB_REF () == 0)
176 {
177 /* sigaction can not fail with SIGINT/SIGQUIT used with old
178 disposition. Same applies for sigprocmask. */
179 __sigaction (SIGINT, &intr, NULL);
180 __sigaction (SIGQUIT, &quit, NULL);
181 __sigprocmask (SIG_SETMASK, &omask, NULL);
182 }
183 DO_UNLOCK ();
184
185 return status;
186}
187
188int
189__libc_system (const char *line)
190{
191 if (line == NULL)
192 /* Check that we have a command processor available. It might
193 not be available after a chroot(), for example. */
194 return do_system ("exit 0") == 0;
195
196 return do_system (line);
197}
198weak_alias (__libc_system, system)
199