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Simon McVittie authored
These more modern locks, introduced in Linux 3.15 and not yet included in POSIX, propagate across fork(), dup(), fd-passing etc. the way you'd expect: as long as at least one copy of the inherited or fd-passed file descriptor remains open, the lock remains held. This allows us to pass a lock fd to a child process across bwrap's fork-and-exec the way we were already trying to, and have it actually work. Signed-off-by:
Simon McVittie <smcv@collabora.com>
Simon McVittie authoredThese more modern locks, introduced in Linux 3.15 and not yet included in POSIX, propagate across fork(), dup(), fd-passing etc. the way you'd expect: as long as at least one copy of the inherited or fd-passed file descriptor remains open, the lock remains held. This allows us to pass a lock fd to a child process across bwrap's fork-and-exec the way we were already trying to, and have it actually work. Signed-off-by:
Simon McVittie <smcv@collabora.com>
with-lock.c 9.50 KiB
/* pressure-vessel-with-lock — run a command with a lock held.
* Basically flock(1), but using fcntl locks compatible with those used
* by bubblewrap and Flatpak.
*
* Copyright © 2019 Collabora Ltd.
*
* SPDX-License-Identifier: LGPL-2.1-or-later
*
* This program 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.
*
* This 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 this library. If not, see <http://www.gnu.org/licenses/>.
*/
#include "config.h"
#include "subprojects/libglnx/config.h"
#include <fcntl.h>
#include <locale.h>
#include <sysexits.h>
#include <sys/prctl.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <glib.h>
#include <glib/gstdio.h>
#include <gio/gio.h>
#include "glib-backports.h"
#include "libglnx.h"
#include "bwrap-lock.h"
#include "utils.h"
#ifndef PR_SET_CHILD_SUBREAPER
#define PR_SET_CHILD_SUBREAPER 36
#endif
static GPtrArray *global_locks = NULL;
static gboolean opt_create = FALSE;
static gboolean opt_subreaper = FALSE;
static gboolean opt_verbose = FALSE;
static gboolean opt_version = FALSE;
static gboolean opt_wait = FALSE;
static gboolean opt_write = FALSE;
static gboolean
opt_fd_cb (const char *name,
const char *value,
gpointer data,
GError **error)
{
char *endptr;
gint64 i64 = g_ascii_strtoll (value, &endptr, 10);
int fd;
int fd_flags;
g_return_val_if_fail (global_locks != NULL, FALSE);
g_return_val_if_fail (error == NULL || *error == NULL, FALSE);
g_return_val_if_fail (value != NULL, FALSE);
if (i64 < 0 || i64 > G_MAXINT || endptr == value || *endptr != '\0')
{
g_set_error (error, G_OPTION_ERROR, G_OPTION_ERROR_BAD_VALUE,
"Integer out of range or invalid: %s", value);
return FALSE;
}
fd = (int) i64;
fd_flags = fcntl (fd, F_GETFD);
if (fd_flags < 0)
return glnx_throw_errno_prefix (error, "Unable to receive --fd %d", fd);
if ((fd_flags & FD_CLOEXEC) == 0
&& fcntl (fd, F_SETFD, fd_flags | FD_CLOEXEC) != 0)
return glnx_throw_errno_prefix (error,
"Unable to configure --fd %d for "
"close-on-exec",
fd);
/* We don't know whether this is an OFD lock or not. Assume it is:
* it won't change our behaviour either way, and if it was passed
* to us across a fork(), it had better be an OFD. */
g_ptr_array_add (global_locks, pv_bwrap_lock_new_take (fd, TRUE));
return TRUE;
}
static gboolean
opt_lock_file_cb (const char *name,
const char *value,
gpointer data,
GError **error)
{
PvBwrapLock *lock;
PvBwrapLockFlags flags = PV_BWRAP_LOCK_FLAGS_NONE;
g_return_val_if_fail (global_locks != NULL, FALSE);
g_return_val_if_fail (error == NULL || *error == NULL, FALSE);
g_return_val_if_fail (value != NULL, FALSE);
if (opt_create)
flags |= PV_BWRAP_LOCK_FLAGS_CREATE;
if (opt_write)
flags |= PV_BWRAP_LOCK_FLAGS_WRITE;
if (opt_wait)
flags |= PV_BWRAP_LOCK_FLAGS_WAIT;
lock = pv_bwrap_lock_new (value, flags, error);
if (lock == NULL)
return FALSE;
g_ptr_array_add (global_locks, lock);
return TRUE;
}
static GOptionEntry options[] =
{
{ "fd", '\0',
G_OPTION_FLAG_NONE, G_OPTION_ARG_CALLBACK, opt_fd_cb,
"Take a file descriptor, already locked if desired, and keep it "
"open. May be repeated.",
NULL },
{ "create", '\0',
G_OPTION_FLAG_NONE, G_OPTION_ARG_NONE, &opt_create,
"Create each subsequent lock file if it doesn't exist.",
NULL },
{ "no-create", '\0',
G_OPTION_FLAG_REVERSE, G_OPTION_ARG_NONE, &opt_create,
"Don't create subsequent nonexistent lock files [default].",
NULL },
{ "write", '\0',
G_OPTION_FLAG_NONE, G_OPTION_ARG_NONE, &opt_write,
"Lock each subsequent lock file for write access.",
NULL },
{ "no-write", '\0',
G_OPTION_FLAG_REVERSE, G_OPTION_ARG_NONE, &opt_write,
"Lock each subsequent lock file for read-only access [default].",
NULL },
{ "wait", '\0',
G_OPTION_FLAG_NONE, G_OPTION_ARG_NONE, &opt_wait,
"Wait for each subsequent lock file.",
NULL },
{ "no-wait", '\0',
G_OPTION_FLAG_REVERSE, G_OPTION_ARG_NONE, &opt_wait,
"Exit unsuccessfully if a lock-file is busy [default].",
NULL },
{ "lock-file", '\0',
G_OPTION_FLAG_NONE, G_OPTION_ARG_CALLBACK, opt_lock_file_cb,
"Open the given file and lock it, affected by options appearing "
"earlier on the command-line. May be repeated.",
NULL },
{ "subreaper", '\0',
G_OPTION_FLAG_NONE, G_OPTION_ARG_NONE, &opt_subreaper,
"Do not exit until all child processes have exited.",
NULL },
{ "no-subreaper", '\0',
G_OPTION_FLAG_REVERSE, G_OPTION_ARG_NONE, &opt_subreaper,
"Only wait for a direct child process [default].",
NULL },
{ "verbose", '\0',
G_OPTION_FLAG_NONE, G_OPTION_ARG_NONE, &opt_verbose,
"Be more verbose.", NULL },
{ "version", '\0',
G_OPTION_FLAG_NONE, G_OPTION_ARG_NONE, &opt_version,
"Print version number and exit.", NULL },
{ NULL }
};
static void
cli_log_func (const gchar *log_domain,
GLogLevelFlags log_level,
const gchar *message,
gpointer user_data)
{
g_printerr ("%s: %s\n", (const char *) user_data, message);
}
int
main (int argc,
char *argv[])
{
g_autoptr(GPtrArray) locks = NULL;
g_autoptr(GOptionContext) context = NULL;
g_autoptr(GError) local_error = NULL;
GError **error = &local_error;
int ret = EX_USAGE;
char **command_and_args;
GPid child_pid;
int wait_status = -1;
setlocale (LC_ALL, "");
pv_avoid_gvfs ();
locks = g_ptr_array_new_with_free_func ((GDestroyNotify) pv_bwrap_lock_free);
global_locks = locks;
g_set_prgname ("pressure-vessel-with-lock");
g_log_set_handler (G_LOG_DOMAIN,
G_LOG_LEVEL_WARNING | G_LOG_LEVEL_MESSAGE,
cli_log_func, (void *) g_get_prgname ());
context = g_option_context_new (
"COMMAND [ARG...]\n"
"Run COMMAND [ARG...] with a lock held, a subreaper, or similar.\n");
g_option_context_add_main_entries (context, options, NULL);
if (!g_option_context_parse (context, &argc, &argv, error))
{
if (g_error_matches (local_error, G_IO_ERROR, G_IO_ERROR_BUSY))
ret = EX_TEMPFAIL;
else if (local_error->domain == G_OPTION_ERROR)
ret = EX_USAGE;
else
ret = EX_UNAVAILABLE;
goto out;
}
if (opt_version)
{
g_print ("%s:\n"
" Package: pressure-vessel\n"
" Version: %s\n",
argv[0], VERSION);
ret = 0;
goto out;
}
if (opt_verbose)
g_log_set_handler (G_LOG_DOMAIN,
G_LOG_LEVEL_DEBUG | G_LOG_LEVEL_INFO,
cli_log_func, (void *) g_get_prgname ());
if (argc >= 2 && strcmp (argv[1], "--") == 0)
{
argv++;
argc--;
}
if (argc < 2)
{
g_printerr ("%s: Usage: %s [OPTIONS] COMMAND [ARG...]\n",
g_get_prgname (),
g_get_prgname ());
goto out;
}
ret = EX_UNAVAILABLE;
command_and_args = argv + 1;
if (opt_subreaper
&& prctl (PR_SET_CHILD_SUBREAPER, 1, 0, 0, 0) != 0)
{
glnx_throw_errno_prefix (error,
"Unable to manage background processes");
goto out;
}
g_debug ("Launching child process...");
if (!g_spawn_async (NULL, /* working directory */
command_and_args,
NULL, /* environment */
G_SPAWN_SEARCH_PATH | G_SPAWN_DO_NOT_REAP_CHILD,
NULL, NULL, /* child setup + user_data */
&child_pid,
&local_error))
{
ret = 127;
goto out;
}
while (1)
{
pid_t died = wait (&wait_status);
if (died < 0)
{
if (errno == EINTR)
{
continue;
}
else if (errno == ECHILD)
{
g_debug ("No more child processes, exiting");
break;
}
else
{
glnx_throw_errno_prefix (error, "wait");
goto out;
}
}
else if (died == child_pid)
{
if (WIFEXITED (wait_status))
{
ret = WEXITSTATUS (wait_status);
g_debug ("Command exited with status %d", ret);
}
else if (WIFSIGNALED (wait_status))
{
ret = 128 + WTERMSIG (wait_status);
g_debug ("Command killed by signal %d", ret - 128);
}
else
{
ret = EX_SOFTWARE;
g_debug ("Command terminated in an unknown way (wait status %d)",
wait_status);
}
}
else
{
g_debug ("Indirect child %lld exited with wait status %d",
(long long) died, wait_status);
g_warn_if_fail (opt_subreaper);
}
}
out:
global_locks = NULL;
if (local_error != NULL)
g_warning ("%s", local_error->message);
return ret;
}