about summary refs log tree commit diff
path: root/sysdeps/posix/system.c
blob: 8a51a6b9919ec39b60b435edc5e89093ce8b695e (plain) (blame)
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
/* Copyright (C) 1991-2018 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
   <http://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);

  TEMP_FAILURE_RETRY (__waitpid_nocancel (args->pid, NULL, 0));

  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;
  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);

  status = __posix_spawn (&pid, SHELL_PATH, 0, &spawn_attr,
			  (char *const[]){ (char*) SHELL_NAME,
					   (char*) "-c",
					   (char *) line, NULL },
			  __environ);
  __posix_spawnattr_destroy (&spawn_attr);

  if (status == 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
    }

  DO_LOCK ();
  if (SUB_REF () == 0)
    {
      /* sigaction can not fail with SIGINT/SIGQUIT used with old
	 disposition.  Same applies for sigprocmask.  */
      __sigaction (SIGINT, &intr, NULL);
      __sigaction (SIGQUIT, &quit, NULL);
      __sigprocmask (SIG_SETMASK, &omask, NULL);
    }
  DO_UNLOCK ();

  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)