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665 lines (597 loc) · 20.7 KB
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/* Copyright (c) 2021, 2026, Oracle and/or its affiliates.
* Copyright (C) 1996-2020 Python Software Foundation
*
* Licensed under the PYTHON SOFTWARE FOUNDATION LICENSE VERSION 2
*/
#ifdef _WIN32
#include <errno.h>
#include <stdint.h>
__declspec(dllexport) int32_t fork_exec(
char *data, int64_t *offsets, int32_t offsetsLen, int32_t argsPos, int32_t envPos, int32_t cwdPos,
int32_t stdinRdFd, int32_t stdinWrFd,
int32_t stdoutRdFd, int32_t stdoutWrFd,
int32_t stderrRdFd, int32_t stderrWrFd,
int32_t errPipeRdFd, int32_t errPipeWrFd,
int32_t closeFds,
int32_t restoreSignals,
int32_t callSetsid,
int32_t pgidToSet,
int32_t allowVFork,
int32_t *fdsToKeep, int64_t fdsToKeepLen
) {
errno = ENOSYS;
return -1;
}
#else
#if defined(__gnu_linux__) && !defined(_GNU_SOURCE)
#define _GNU_SOURCE 1
#endif
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#if defined(__linux__)
#include <sys/syscall.h>
#endif
#include <dirent.h>
#include <errno.h>
#include <assert.h>
#include <string.h>
#include <limits.h>
#include <signal.h>
#include "errno_capture.h"
// These definitions emulate CPython's equivalents so that the copy&pasted code below works without too many changes
#define HAVE_DIRFD 1
#define HAVE_SETSID 1
#if defined(__GNUC__) || defined(__clang__)
#define Py_NO_INLINE __attribute__((noinline))
#elif defined(_MSC_VER)
#define Py_NO_INLINE __declspec(noinline)
#else
#define Py_NO_INLINE
#endif
#if defined(__linux__)
/* If this is ever expanded to non-Linux platforms, verify what calls are
* allowed after vfork(). Ex: setsid() may be disallowed on macOS? */
#define VFORK_USABLE 1
#endif
int32_t set_inheritable(int32_t fd, int32_t inheritable);
// TODO JDK also handles EINTR for dup2 calls
// TODO neither CPython nor JDK handle EINTR returned from close(), see NOTES on man page for close(2)
static const char *Py_hexdigits = "0123456789abcdef";
static int
_Py_set_inheritable_async_safe(int fd, int inheritable, int *atomic_flag_works)
{
assert(atomic_flag_works == NULL);
return set_inheritable(fd, inheritable);
}
static void
_Py_write_noraise(int fd, const void *buf, size_t count)
{
while (write(fd, buf, count) < 0 && errno == EINTR)
;
}
static void
_Py_RestoreSignals()
{
}
// The following code is taken directly from CPython's _posixsubprocess.c with some minor changes:
// - py_fds_to_keep is not a PyObject, but an int array
// - there's no preexec_fn
#if defined(__FreeBSD__) || (defined(__APPLE__) && defined(__MACH__))
# define FD_DIR "/dev/fd"
#else
# define FD_DIR "/proc/self/fd"
#endif
#define POSIX_CALL(call) do { if ((call) == -1) goto error; } while (0)
/* Convert ASCII to a positive int, no libc call. no overflow. -1 on error. */
static int
_pos_int_from_ascii(const char *name)
{
int num = 0;
while (*name >= '0' && *name <= '9') {
num = num * 10 + (*name - '0');
++name;
}
if (*name)
return -1; /* Non digit found, not a number. */
return num;
}
/* Is fd found in the sorted Python Sequence? */
static int
_is_fd_in_sorted_fd_sequence(int fd, int *fd_sequence, ssize_t fd_sequence_len)
{
/* Binary search. */
ssize_t search_min = 0;
ssize_t search_max = fd_sequence_len - 1;
if (search_max < 0)
return 0;
do {
long middle = (search_min + search_max) / 2;
int middle_fd = fd_sequence[middle];
if (fd == middle_fd)
return 1;
if (fd > middle_fd)
search_min = middle + 1;
else
search_max = middle - 1;
} while (search_min <= search_max);
return 0;
}
static int
make_inheritable(int *fds_to_keep, ssize_t len, int errpipe_write)
{
ssize_t i;
for (i = 0; i < len; ++i) {
int fd = fds_to_keep[i];
assert(0 <= fd && fd <= INT_MAX);
if (fd == errpipe_write) {
/* errpipe_write is part of py_fds_to_keep. It must be closed at
exec(), but kept open in the child process until exec() is
called. */
continue;
}
if (_Py_set_inheritable_async_safe(fd, 1, NULL) < 0)
return -1;
}
return 0;
}
/* Get the maximum file descriptor that could be opened by this process.
* This function is async signal safe for use between fork() and exec().
*/
static long
safe_get_max_fd(void)
{
long local_max_fd;
#if defined(__NetBSD__)
local_max_fd = fcntl(0, F_MAXFD);
if (local_max_fd >= 0)
return local_max_fd;
#endif
#if defined(HAVE_SYS_RESOURCE_H) && defined(__OpenBSD__)
struct rlimit rl;
/* Not on the POSIX async signal safe functions list but likely
* safe. TODO - Someone should audit OpenBSD to make sure. */
if (getrlimit(RLIMIT_NOFILE, &rl) >= 0)
return (long) rl.rlim_max;
#endif
#ifdef _SC_OPEN_MAX
local_max_fd = sysconf(_SC_OPEN_MAX);
if (local_max_fd == -1)
#endif
local_max_fd = 256; /* Matches legacy Lib/subprocess.py behavior. */
return local_max_fd;
}
/* Close all file descriptors in the range from start_fd and higher
* except for those in py_fds_to_keep. If the range defined by
* [start_fd, safe_get_max_fd()) is large this will take a long
* time as it calls close() on EVERY possible fd.
*
* It isn't possible to know for sure what the max fd to go up to
* is for processes with the capability of raising their maximum.
*/
static void
_close_fds_by_brute_force(long start_fd, int *fds_to_keep, ssize_t num_fds_to_keep)
{
long end_fd = safe_get_max_fd();
ssize_t keep_seq_idx;
int fd_num;
/* As py_fds_to_keep is sorted we can loop through the list closing
* fds in between any in the keep list falling within our range. */
for (keep_seq_idx = 0; keep_seq_idx < num_fds_to_keep; ++keep_seq_idx) {
int keep_fd = fds_to_keep[keep_seq_idx];
if (keep_fd < start_fd)
continue;
for (fd_num = start_fd; fd_num < keep_fd; ++fd_num) {
close(fd_num);
}
start_fd = keep_fd + 1;
}
if (start_fd <= end_fd) {
for (fd_num = start_fd; fd_num < end_fd; ++fd_num) {
close(fd_num);
}
}
}
#if defined(__linux__) && defined(SYS_getdents64)
struct linux_dirent64 {
unsigned long long d_ino;
long long d_off;
unsigned short d_reclen;
unsigned char d_type;
char d_name[256];
};
static void
_close_open_fds_safe(long start_fd, int *fds_to_keep, ssize_t fds_to_keep_len)
{
int fd_dir_fd = open(FD_DIR, O_RDONLY);
if (fd_dir_fd == -1) {
_close_fds_by_brute_force(start_fd, fds_to_keep, fds_to_keep_len);
return;
}
char buffer[sizeof(struct linux_dirent64)];
int bytes;
while ((bytes = syscall(SYS_getdents64, fd_dir_fd, (struct linux_dirent64 *)buffer, sizeof(buffer))) > 0) {
struct linux_dirent64 *entry;
int offset;
for (offset = 0; offset < bytes; offset += entry->d_reclen) {
int fd;
entry = (struct linux_dirent64 *)(buffer + offset);
if ((fd = _pos_int_from_ascii(entry->d_name)) < 0)
continue;
if (fd != fd_dir_fd && fd >= start_fd &&
!_is_fd_in_sorted_fd_sequence(fd, fds_to_keep, fds_to_keep_len)) {
close(fd);
}
}
}
close(fd_dir_fd);
}
#define _close_open_fds _close_open_fds_safe
#else
/* Close all open file descriptors from start_fd and higher.
* Do not close any in the sorted py_fds_to_keep tuple.
*
* This function violates the strict use of async signal safe functions. :(
* It calls opendir(), readdir() and closedir(). Of these, the one most
* likely to ever cause a problem is opendir() as it performs an internal
* malloc(). Practically this should not be a problem. The Java VM makes the
* same calls between fork and exec in its own UNIXProcess_md.c implementation.
*
* readdir_r() is not used because it provides no benefit. It is typically
* implemented as readdir() followed by memcpy(). See also:
* http://womble.decadent.org.uk/readdir_r-advisory.html
*/
static void
_close_open_fds_maybe_unsafe(long start_fd, int* fds_to_keep, ssize_t fds_to_keep_len)
{
DIR *proc_fd_dir;
#ifndef HAVE_DIRFD
while (_is_fd_in_sorted_fd_sequence(start_fd, fds_to_keep, fds_to_keep_len)) {
++start_fd;
}
/* Close our lowest fd before we call opendir so that it is likely to
* reuse that fd otherwise we might close opendir's file descriptor in
* our loop. This trick assumes that fd's are allocated on a lowest
* available basis. */
close(start_fd);
++start_fd;
#endif
#if defined(__FreeBSD__)
if (!_is_fdescfs_mounted_on_dev_fd())
proc_fd_dir = NULL;
else
#endif
proc_fd_dir = opendir(FD_DIR);
if (!proc_fd_dir) {
/* No way to get a list of open fds. */
_close_fds_by_brute_force(start_fd, fds_to_keep, fds_to_keep_len);
} else {
struct dirent *dir_entry;
#ifdef HAVE_DIRFD
int fd_used_by_opendir = dirfd(proc_fd_dir);
#else
int fd_used_by_opendir = start_fd - 1;
#endif
errno = 0;
while ((dir_entry = readdir(proc_fd_dir))) {
int fd;
if ((fd = _pos_int_from_ascii(dir_entry->d_name)) < 0)
continue; /* Not a number. */
if (fd != fd_used_by_opendir && fd >= start_fd &&
!_is_fd_in_sorted_fd_sequence(fd, fds_to_keep, fds_to_keep_len)) {
close(fd);
}
errno = 0;
}
if (errno) {
/* readdir error, revert behavior. Highly Unlikely. */
_close_fds_by_brute_force(start_fd, fds_to_keep, fds_to_keep_len);
}
closedir(proc_fd_dir);
}
}
#define _close_open_fds _close_open_fds_maybe_unsafe
#endif
#ifdef VFORK_USABLE
static void
reset_signal_handlers(const sigset_t *child_sigmask)
{
struct sigaction sa_dfl = {.sa_handler = SIG_DFL};
for (int sig = 1; sig < _NSIG; sig++) {
if (sig == SIGKILL || sig == SIGSTOP) {
continue;
}
if (sigismember(child_sigmask, sig) == 1) {
continue;
}
struct sigaction sa;
if (sigaction(sig, NULL, &sa) == -1) {
continue;
}
void *h = (sa.sa_flags & SA_SIGINFO ? (void *)sa.sa_sigaction :
(void *)sa.sa_handler);
if (h == SIG_IGN || h == SIG_DFL) {
continue;
}
(void) sigaction(sig, &sa_dfl, NULL);
}
}
#endif
/*
* This function is code executed in the child process immediately after fork
* to set things up and call exec().
*
* All of the code in this function must only use async-signal-safe functions,
* listed at `man 7 signal` or
* http://www.opengroup.org/onlinepubs/009695399/functions/xsh_chap02_04.html.
*
* This restriction is documented at
* http://www.opengroup.org/onlinepubs/009695399/functions/fork.html.
*
* If this function is called after vfork(), even more care must be taken.
* The child shares the parent's address space until execve() or _exit().
*/
Py_NO_INLINE static void
child_exec(char *const exec_array[],
char *const argv[],
char *const envp[],
const char *cwd,
int p2cread, int p2cwrite,
int c2pread, int c2pwrite,
int errread, int errwrite,
int errpipe_read, int errpipe_write,
int close_fds, int restore_signals,
int call_setsid,
int pgid_to_set,
const void *child_sigmask,
int *fds_to_keep,
ssize_t fds_to_keep_len)
{
int i, saved_errno;
/* Buffer large enough to hold a hex integer. We can't malloc. */
char hex_errno[sizeof(saved_errno)*2+1];
const char *err_msg = "noexec";
if (make_inheritable(fds_to_keep, fds_to_keep_len, errpipe_write) < 0)
goto error;
/* Close parent's pipe ends. */
if (p2cwrite != -1)
POSIX_CALL(close(p2cwrite));
if (c2pread != -1)
POSIX_CALL(close(c2pread));
if (errread != -1)
POSIX_CALL(close(errread));
POSIX_CALL(close(errpipe_read));
/* When duping fds, if there arises a situation where one of the fds is
either 0, 1 or 2, it is possible that it is overwritten (#12607). */
if (c2pwrite == 0) {
POSIX_CALL(c2pwrite = dup(c2pwrite));
/* issue32270 */
if (_Py_set_inheritable_async_safe(c2pwrite, 0, NULL) < 0) {
goto error;
}
}
while (errwrite == 0 || errwrite == 1) {
POSIX_CALL(errwrite = dup(errwrite));
/* issue32270 */
if (_Py_set_inheritable_async_safe(errwrite, 0, NULL) < 0) {
goto error;
}
}
/* Dup fds for child.
dup2() removes the CLOEXEC flag but we must do it ourselves if dup2()
would be a no-op (issue #10806). */
if (p2cread == 0) {
if (_Py_set_inheritable_async_safe(p2cread, 1, NULL) < 0)
goto error;
}
else if (p2cread != -1)
POSIX_CALL(dup2(p2cread, 0)); /* stdin */
if (c2pwrite == 1) {
if (_Py_set_inheritable_async_safe(c2pwrite, 1, NULL) < 0)
goto error;
}
else if (c2pwrite != -1)
POSIX_CALL(dup2(c2pwrite, 1)); /* stdout */
if (errwrite == 2) {
if (_Py_set_inheritable_async_safe(errwrite, 1, NULL) < 0)
goto error;
}
else if (errwrite != -1)
POSIX_CALL(dup2(errwrite, 2)); /* stderr */
/* We no longer manually close p2cread, c2pwrite, and errwrite here as
* _close_open_fds takes care when it is not already non-inheritable. */
if (cwd) {
if (chdir(cwd) == -1) {
err_msg = "noexec:chdir";
goto error;
}
}
if (restore_signals)
_Py_RestoreSignals();
#ifdef VFORK_USABLE
if (child_sigmask) {
reset_signal_handlers((const sigset_t *)child_sigmask);
if ((errno = pthread_sigmask(SIG_SETMASK, child_sigmask, NULL))) {
goto error;
}
}
#endif
#ifdef HAVE_SETSID
if (call_setsid)
POSIX_CALL(setsid());
#endif
if (pgid_to_set >= 0)
POSIX_CALL(setpgid(0, pgid_to_set));
err_msg = "";
/* close FDs after executing preexec_fn, which might open FDs */
if (close_fds) {
/* TODO HP-UX could use pstat_getproc() if anyone cares about it. */
_close_open_fds(3, fds_to_keep, fds_to_keep_len);
}
/* This loop matches the Lib/os.py _execvpe()'s PATH search when */
/* given the executable_list generated by Lib/subprocess.py. */
saved_errno = 0;
for (i = 0; exec_array[i] != NULL; ++i) {
const char *executable = exec_array[i];
if (envp) {
execve(executable, argv, envp);
} else {
execv(executable, argv);
}
if (errno != ENOENT && errno != ENOTDIR && saved_errno == 0) {
saved_errno = errno;
}
}
/* Report the first exec error, not the last. */
if (saved_errno)
errno = saved_errno;
error:
saved_errno = errno;
/* Report the posix error to our parent process. */
/* We ignore all write() return values as the total size of our writes is
less than PIPEBUF and we cannot do anything about an error anyways.
Use _Py_write_noraise() to retry write() if it is interrupted by a
signal (fails with EINTR). */
if (saved_errno) {
char *cur;
_Py_write_noraise(errpipe_write, "OSError:", 8);
cur = hex_errno + sizeof(hex_errno);
while (saved_errno != 0 && cur != hex_errno) {
*--cur = Py_hexdigits[saved_errno % 16];
saved_errno /= 16;
}
_Py_write_noraise(errpipe_write, cur, hex_errno + sizeof(hex_errno) - cur);
_Py_write_noraise(errpipe_write, ":", 1);
/* We can't call strerror(saved_errno). It is not async signal safe.
* The parent process will look the error message up. */
} else {
_Py_write_noraise(errpipe_write, "SubprocessError:0:", 18);
}
_Py_write_noraise(errpipe_write, err_msg, strlen(err_msg));
}
Py_NO_INLINE static pid_t
do_fork_exec(char *const exec_list[],
char *const argv[],
char *const envp[],
const char *cwd,
int stdinRdFd, int stdinWrFd,
int stdoutRdFd, int stdoutWrFd,
int stderrRdFd, int stderrWrFd,
int errPipeRdFd, int errPipeWrFd,
int closeFds, int restoreSignals,
int callSetsid,
int pgidToSet,
const void *childSigmask,
int *fdsToKeep, int64_t fdsToKeepLen)
{
pid_t pid;
#ifdef VFORK_USABLE
if (childSigmask) {
pid = vfork();
} else
#endif
{
pid = fork();
}
if (pid != 0) {
return pid;
}
child_exec(
exec_list, argv, envp, cwd,
stdinRdFd, stdinWrFd,
stdoutRdFd, stdoutWrFd,
stderrRdFd, stderrWrFd,
errPipeRdFd, errPipeWrFd,
closeFds,
restoreSignals,
callSetsid,
pgidToSet,
childSigmask,
fdsToKeep, fdsToKeepLen
);
_exit(255);
}
/*
* data, offsets, offsetsLen, argsPos, envPos, cwdPos - see comment in NativePosixSupport.forkExec()
* stdinRdFd - read end of the pipe for the child's stdin - closed by parent, dupped to fd 0 by child
* stdinWrFd - write end of the pipe for the child's stdin - closed by child, written to by parent
* stdoutRdFd - read end of the pipe for the child's stdout - closed by child, read from by parent
* stdoutWrFd - write end of the pipe for the child's stdout - closed by parent, dupped to fd 1 by child
* stderrRdFd - read end of the pipe for the child's stderr - closed by child, read from by parent
* stderrWrFd - write end of the pipe for the child's stderr - closed by parent, dupped to fd 2 by child
* errPipeRdFd - read end of the pipe for reporting exec errors to parent - closed by child, read from by parent
* errPipeWrFd - write end of the pipe for reporting exec errors to parent - closed by parent, written to by child if an error occurs
- the child process closes this fd in any case:
- on success, no data is written and the fd is closed by exec() because its O_CLOEXEC is set
- on error, the error code is written and the fd is closed because the child process exits
* closeFds - nonzero if all fds except 0, 1, 2 and those in fdsToKeep should be explicitly closed by the child
* (if nonzero, then errPipeWrFd must be in fdsToKeep)
* restoreSignals - currently not used
* callSetsid - if nonzero, the child calls setsid before exec()
* pgidToSet - if non-negative, the child calls setpgid(0, pgidToSet) before exec()
* allowVFork - if nonzero, use vfork() instead of fork() where it is safe and supported
* fdsToKeep, fdsToKeepLen - a sorted list of fds to keep open (the child clears their O_CLOEXEC)
*/
int32_t fork_exec(
char *data, int64_t *offsets, int32_t offsetsLen, int32_t argsPos, int32_t envPos, int32_t cwdPos,
int32_t stdinRdFd, int32_t stdinWrFd,
int32_t stdoutRdFd, int32_t stdoutWrFd,
int32_t stderrRdFd, int32_t stderrWrFd,
int32_t errPipeRdFd, int32_t errPipeWrFd,
int32_t closeFds,
int32_t restoreSignals,
int32_t callSetsid,
int32_t pgidToSet,
int32_t allowVFork,
int32_t *fdsToKeep, int64_t fdsToKeepLen
) {
// We reuse the memory allocated for offsets to avoid the need to allocate and reliably free another array
char **strings = (char **) offsets;
for (int32_t i = 0; i < offsetsLen; ++i) {
strings[i] = offsets[i] == -1 ? NULL : data + offsets[i];
}
char **exec_list = strings;
char **argv = strings + argsPos;
char **envp = envPos == -1 ? NULL : strings + envPos;
char *cwd = cwdPos == -1 ? NULL : strings[cwdPos];
#ifdef VFORK_USABLE
const void *oldSigmask = NULL;
sigset_t oldSigs;
/* Keep process-group setup on the normal fork path. */
if (allowVFork && pgidToSet < 0) {
sigset_t allSigs;
sigfillset(&allSigs);
int err = pthread_sigmask(SIG_BLOCK, &allSigs, &oldSigs);
if (err) {
errno = err;
capture_errno();
return -1;
}
oldSigmask = &oldSigs;
}
#else
const void *oldSigmask = NULL;
#endif
pid_t pid = do_fork_exec(
exec_list, argv, envp, cwd,
stdinRdFd, stdinWrFd,
stdoutRdFd, stdoutWrFd,
stderrRdFd, stderrWrFd,
errPipeRdFd, errPipeWrFd,
closeFds,
restoreSignals,
callSetsid,
pgidToSet,
oldSigmask,
fdsToKeep, fdsToKeepLen
);
#ifdef VFORK_USABLE
if (oldSigmask) {
(void) pthread_sigmask(SIG_SETMASK, oldSigmask, NULL);
}
#endif
capture_errno();
return pid;
}
#endif