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glnx-backports.c
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glnx-backports.c
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/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*-
*
* Copyright 2000-2022 Red Hat, Inc.
* Copyright 2006-2007 Matthias Clasen
* Copyright 2006 Padraig O'Briain
* Copyright 2007 Lennart Poettering
* Copyright (C) 2015 Colin Walters <walters@verbum.org>
* Copyright 2018-2022 Endless OS Foundation, LLC
* Copyright 2018 Peter Wu
* Copyright 2019 Ting-Wei Lan
* Copyright 2019 Sebastian Schwarz
* Copyright 2020 Matt Rose
* Copyright 2021 Casper Dik
* Copyright 2022 Alexander Richardson
* Copyright 2022 Ray Strode
* Copyright 2022 Thomas Haller
* Copyright 2023-2024 Collabora Ltd.
* Copyright 2023 Sebastian Wilhelmi
* Copyright 2023 CaiJingLong
* SPDX-License-Identifier: LGPL-2.1-or-later
*
* This 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 licence 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 "libglnx-config.h"
#include "glnx-backports.h"
#include "glnx-missing.h"
#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <stdlib.h>
#include <sys/resource.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>
#if !GLIB_CHECK_VERSION(2, 44, 0)
gboolean
glnx_strv_contains (const gchar * const *strv,
const gchar *str)
{
g_return_val_if_fail (strv != NULL, FALSE);
g_return_val_if_fail (str != NULL, FALSE);
for (; *strv != NULL; strv++)
{
if (g_str_equal (str, *strv))
return TRUE;
}
return FALSE;
}
gboolean
glnx_set_object (GObject **object_ptr,
GObject *new_object)
{
GObject *old_object = *object_ptr;
if (old_object == new_object)
return FALSE;
if (new_object != NULL)
g_object_ref (new_object);
*object_ptr = new_object;
if (old_object != NULL)
g_object_unref (old_object);
return TRUE;
}
#endif
#if !GLIB_CHECK_VERSION(2, 60, 0)
gboolean
_glnx_strv_equal (const gchar * const *strv1,
const gchar * const *strv2)
{
g_return_val_if_fail (strv1 != NULL, FALSE);
g_return_val_if_fail (strv2 != NULL, FALSE);
if (strv1 == strv2)
return TRUE;
for (; *strv1 != NULL && *strv2 != NULL; strv1++, strv2++)
{
if (!g_str_equal (*strv1, *strv2))
return FALSE;
}
return (*strv1 == NULL && *strv2 == NULL);
}
#endif
#if !GLIB_CHECK_VERSION(2, 80, 0)
/* This function is called between fork() and exec() and hence must be
* async-signal-safe (see signal-safety(7)). */
static int
set_cloexec (void *data, gint fd)
{
if (fd >= GPOINTER_TO_INT (data))
fcntl (fd, F_SETFD, FD_CLOEXEC);
return 0;
}
/* fdwalk()-compatible callback to close a fd for non-compliant
* implementations of fdwalk() that potentially pass already
* closed fds.
*
* It is not an error to pass an invalid fd to this function.
*
* This function is called between fork() and exec() and hence must be
* async-signal-safe (see signal-safety(7)).
*/
G_GNUC_UNUSED static int
close_func_with_invalid_fds (void *data, int fd)
{
/* We use close and not g_close here because on some platforms, we
* don't know how to close only valid, open file descriptors, so we
* have to pass bad fds to close too. g_close warns if given a bad
* fd.
*
* This function returns no error, because there is nothing that the caller
* could do with that information. That is even the case for EINTR. See
* g_close() about the specialty of EINTR and why that is correct.
* If g_close() ever gets extended to handle EINTR specially, then this place
* should get updated to do the same handling.
*/
if (fd >= GPOINTER_TO_INT (data))
close (fd);
return 0;
}
#ifdef __linux__
struct linux_dirent64
{
guint64 d_ino; /* 64-bit inode number */
guint64 d_off; /* 64-bit offset to next structure */
unsigned short d_reclen; /* Size of this dirent */
unsigned char d_type; /* File type */
char d_name[]; /* Filename (null-terminated) */
};
/* This function is called between fork() and exec() and hence must be
* async-signal-safe (see signal-safety(7)). */
static gint
filename_to_fd (const char *p)
{
char c;
int fd = 0;
const int cutoff = G_MAXINT / 10;
const int cutlim = G_MAXINT % 10;
if (*p == '\0')
return -1;
while ((c = *p++) != '\0')
{
if (c < '0' || c > '9')
return -1;
c -= '0';
/* Check for overflow. */
if (fd > cutoff || (fd == cutoff && c > cutlim))
return -1;
fd = fd * 10 + c;
}
return fd;
}
#endif
static int safe_fdwalk_with_invalid_fds (int (*cb)(void *data, int fd), void *data);
/* This function is called between fork() and exec() and hence must be
* async-signal-safe (see signal-safety(7)). */
static int
safe_fdwalk (int (*cb)(void *data, int fd), void *data)
{
#if 0
/* Use fdwalk function provided by the system if it is known to be
* async-signal safe.
*
* Currently there are no operating systems known to provide a safe
* implementation, so this section is not used for now.
*/
return fdwalk (cb, data);
#else
/* Fallback implementation of fdwalk. It should be async-signal safe, but it
* may fail on non-Linux operating systems. See safe_fdwalk_with_invalid_fds
* for a slower alternative.
*/
#ifdef __linux__
gint fd;
gint res = 0;
/* Avoid use of opendir/closedir since these are not async-signal-safe. */
int dir_fd = open ("/proc/self/fd", O_RDONLY | O_DIRECTORY);
if (dir_fd >= 0)
{
/* buf needs to be aligned correctly to receive linux_dirent64.
* C11 has _Alignof for this purpose, but for now a
* union serves the same purpose. */
union
{
char buf[4096];
struct linux_dirent64 alignment;
} u;
int pos, nread;
struct linux_dirent64 *de;
while ((nread = syscall (SYS_getdents64, dir_fd, u.buf, sizeof (u.buf))) > 0)
{
for (pos = 0; pos < nread; pos += de->d_reclen)
{
de = (struct linux_dirent64 *) (u.buf + pos);
fd = filename_to_fd (de->d_name);
if (fd < 0 || fd == dir_fd)
continue;
if ((res = cb (data, fd)) != 0)
break;
}
}
close (dir_fd);
return res;
}
/* If /proc is not mounted or not accessible we fail here and rely on
* safe_fdwalk_with_invalid_fds to fall back to the old
* rlimit trick. */
#endif
#if defined(__sun__) && defined(F_PREVFD) && defined(F_NEXTFD)
/*
* Solaris 11.4 has a signal-safe way which allows
* us to find all file descriptors in a process.
*
* fcntl(fd, F_NEXTFD, maxfd)
* - returns the first allocated file descriptor <= maxfd > fd.
*
* fcntl(fd, F_PREVFD)
* - return highest allocated file descriptor < fd.
*/
gint fd;
gint res = 0;
open_max = fcntl (INT_MAX, F_PREVFD); /* find the maximum fd */
if (open_max < 0) /* No open files */
return 0;
for (fd = -1; (fd = fcntl (fd, F_NEXTFD, open_max)) != -1; )
if ((res = cb (data, fd)) != 0 || fd == open_max)
break;
return res;
#endif
return safe_fdwalk_with_invalid_fds (cb, data);
#endif
}
/* This function is called between fork() and exec() and hence must be
* async-signal-safe (see signal-safety(7)). */
static int
safe_fdwalk_with_invalid_fds (int (*cb)(void *data, int fd), void *data)
{
/* Fallback implementation of fdwalk. It should be async-signal safe, but it
* may be slow, especially on systems allowing very high number of open file
* descriptors.
*/
gint open_max = -1;
gint fd;
gint res = 0;
#if 0 && defined(HAVE_SYS_RESOURCE_H)
struct rlimit rl;
/* Use getrlimit() function provided by the system if it is known to be
* async-signal safe.
*
* Currently there are no operating systems known to provide a safe
* implementation, so this section is not used for now.
*/
if (getrlimit (RLIMIT_NOFILE, &rl) == 0 && rl.rlim_max != RLIM_INFINITY)
open_max = rl.rlim_max;
#endif
#if defined(__FreeBSD__) || defined(__OpenBSD__) || defined(__APPLE__)
/* Use sysconf() function provided by the system if it is known to be
* async-signal safe.
*
* FreeBSD: sysconf() is included in the list of async-signal safe functions
* found in https://man.freebsd.org/sigaction(2).
*
* OpenBSD: sysconf() is included in the list of async-signal safe functions
* found in https://man.openbsd.org/sigaction.2.
*
* Apple: sysconf() is included in the list of async-signal safe functions
* found in https://opensource.apple.com/source/xnu/xnu-517.12.7/bsd/man/man2/sigaction.2
*/
if (open_max < 0)
open_max = sysconf (_SC_OPEN_MAX);
#endif
/* Hardcoded fallback: the default process hard limit in Linux as of 2020 */
if (open_max < 0)
open_max = 4096;
#if defined(__APPLE__) && defined(HAVE_LIBPROC_H)
/* proc_pidinfo isn't documented as async-signal-safe but looking at the implementation
* in the darwin tree here:
*
* https://opensource.apple.com/source/Libc/Libc-498/darwin/libproc.c.auto.html
*
* It's just a thin wrapper around a syscall, so it's probably okay.
*/
{
char buffer[4096 * PROC_PIDLISTFD_SIZE];
ssize_t buffer_size;
buffer_size = proc_pidinfo (getpid (), PROC_PIDLISTFDS, 0, buffer, sizeof (buffer));
if (buffer_size > 0 &&
sizeof (buffer) >= (size_t) buffer_size &&
(buffer_size % PROC_PIDLISTFD_SIZE) == 0)
{
const struct proc_fdinfo *fd_info = (const struct proc_fdinfo *) buffer;
size_t number_of_fds = (size_t) buffer_size / PROC_PIDLISTFD_SIZE;
for (size_t i = 0; i < number_of_fds; i++)
if ((res = cb (data, fd_info[i].proc_fd)) != 0)
break;
return res;
}
}
#endif
for (fd = 0; fd < open_max; fd++)
if ((res = cb (data, fd)) != 0)
break;
return res;
}
/**
* g_fdwalk_set_cloexec:
* @lowfd: Minimum fd to act on, which must be non-negative
*
* Mark every file descriptor equal to or greater than @lowfd to be closed
* at the next `execve()` or similar, as if via the `FD_CLOEXEC` flag.
*
* Typically @lowfd will be 3, to leave standard input, standard output
* and standard error open after exec.
*
* This is the same as Linux `close_range (lowfd, ~0U, CLOSE_RANGE_CLOEXEC)`,
* but portable to other OSs and to older versions of Linux.
*
* This function is async-signal safe, making it safe to call from a
* signal handler or a [callback@GLib.SpawnChildSetupFunc], as long as @lowfd is
* non-negative.
* See [`signal(7)`](man:signal(7)) and
* [`signal-safety(7)`](man:signal-safety(7)) for more details.
*
* Returns: 0 on success, -1 with errno set on error
* Since: 2.80
*/
int
_glnx_fdwalk_set_cloexec (int lowfd)
{
int ret;
g_return_val_if_fail (lowfd >= 0, (errno = EINVAL, -1));
#if defined(HAVE_CLOSE_RANGE) && defined(CLOSE_RANGE_CLOEXEC)
/* close_range() is available in Linux since kernel 5.9, and on FreeBSD at
* around the same time. It was designed for use in async-signal-safe
* situations: https://bugs.python.org/issue38061
*
* The `CLOSE_RANGE_CLOEXEC` flag was added in Linux 5.11, and is not yet
* present in FreeBSD.
*
* Handle ENOSYS in case it’s supported in libc but not the kernel; if so,
* fall back to safe_fdwalk(). Handle EINVAL in case `CLOSE_RANGE_CLOEXEC`
* is not supported. */
ret = close_range (lowfd, G_MAXUINT, CLOSE_RANGE_CLOEXEC);
if (ret == 0 || !(errno == ENOSYS || errno == EINVAL))
return ret;
#endif /* HAVE_CLOSE_RANGE */
ret = safe_fdwalk (set_cloexec, GINT_TO_POINTER (lowfd));
return ret;
}
/**
* g_closefrom:
* @lowfd: Minimum fd to close, which must be non-negative
*
* Close every file descriptor equal to or greater than @lowfd.
*
* Typically @lowfd will be 3, to leave standard input, standard output
* and standard error open.
*
* This is the same as Linux `close_range (lowfd, ~0U, 0)`,
* but portable to other OSs and to older versions of Linux.
* Equivalently, it is the same as BSD `closefrom (lowfd)`, but portable,
* and async-signal-safe on all OSs.
*
* This function is async-signal safe, making it safe to call from a
* signal handler or a [callback@GLib.SpawnChildSetupFunc], as long as @lowfd is
* non-negative.
* See [`signal(7)`](man:signal(7)) and
* [`signal-safety(7)`](man:signal-safety(7)) for more details.
*
* Returns: 0 on success, -1 with errno set on error
* Since: 2.80
*/
int
_glnx_closefrom (int lowfd)
{
int ret;
g_return_val_if_fail (lowfd >= 0, (errno = EINVAL, -1));
#if defined(HAVE_CLOSE_RANGE)
/* close_range() is available in Linux since kernel 5.9, and on FreeBSD at
* around the same time. It was designed for use in async-signal-safe
* situations: https://bugs.python.org/issue38061
*
* Handle ENOSYS in case it’s supported in libc but not the kernel; if so,
* fall back to safe_fdwalk(). */
ret = close_range (lowfd, G_MAXUINT, 0);
if (ret == 0 || errno != ENOSYS)
return ret;
#endif /* HAVE_CLOSE_RANGE */
#if defined(__FreeBSD__) || defined(__OpenBSD__) || \
(defined(__sun__) && defined(F_CLOSEFROM))
/* Use closefrom function provided by the system if it is known to be
* async-signal safe.
*
* FreeBSD: closefrom is included in the list of async-signal safe functions
* found in https://man.freebsd.org/sigaction(2).
*
* OpenBSD: closefrom is not included in the list, but a direct system call
* should be safe to use.
*
* In Solaris as of 11.3 SRU 31, closefrom() is also a direct system call.
* On such systems, F_CLOSEFROM is defined.
*/
(void) closefrom (lowfd);
return 0;
#elif defined(__DragonFly__)
/* It is unclear whether closefrom function included in DragonFlyBSD libc_r
* is safe to use because it calls a lot of library functions. It is also
* unclear whether libc_r itself is still being used. Therefore, we do a
* direct system call here ourselves to avoid possible issues.
*/
(void) syscall (SYS_closefrom, lowfd);
return 0;
#elif defined(F_CLOSEM)
/* NetBSD and AIX have a special fcntl command which does the same thing as
* closefrom. NetBSD also includes closefrom function, which seems to be a
* simple wrapper of the fcntl command.
*/
return fcntl (lowfd, F_CLOSEM);
#else
ret = safe_fdwalk (close_func_with_invalid_fds, GINT_TO_POINTER (lowfd));
return ret;
#endif
}
#endif /* !2.80.0 */