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Don't restrict ourselves to a "max" fd when closing fds before exec() 

when we have a way to get an actual list of all open fds from the OS.

Fixes issue #21618: The subprocess module would ignore fds that were
inherited by the calling process and already higher than POSIX resource
limits would otherwise allow.  On systems with a functioning /proc/self/fd
or /dev/fd interface the max is now ignored and all fds are closed.
This commit is contained in:
Gregory P. Smith 2014-06-01 13:18:28 -07:00
parent 694c3153b0
commit d4dcb70287
3 changed files with 102 additions and 43 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

53
Lib/test/test_subprocess.py
View File

@ -1926,6 +1926,59 @@ class POSIXProcessTestCase(BaseTestCase):
"Some fds not in pass_fds were left open")
self.assertIn(1, remaining_fds, "Subprocess failed")
def test_close_fds_when_max_fd_is_lowered(self):
"""Confirm that issue21618 is fixed (may fail under valgrind)."""
fd_status = support.findfile("fd_status.py", subdir="subprocessdata")
open_fds = set()
# Add a bunch more fds to pass down.
for _ in range(10):
fd = os.open("/dev/null", os.O_RDONLY)
open_fds.add(fd)
# Leave a two pairs of low ones available for use by the
# internal child error pipe and the stdout pipe.
for fd in sorted(open_fds)[:4]:
os.close(fd)
open_fds.remove(fd)
for fd in open_fds:
self.addCleanup(os.close, fd)
os.set_inheritable(fd, True)
max_fd_open = max(open_fds)
import resource
rlim_cur, rlim_max = resource.getrlimit(resource.RLIMIT_NOFILE)
try:
# 9 is lower than the highest fds we are leaving open.
resource.setrlimit(resource.RLIMIT_NOFILE, (9, rlim_max))
# Launch a new Python interpreter with our low fd rlim_cur that
# inherits open fds above that limit. It then uses subprocess
# with close_fds=True to get a report of open fds in the child.
# An explicit list of fds to check is passed to fd_status.py as
# letting fd_status rely on its default logic would miss the
# fds above rlim_cur as it normally only checks up to that limit.
p = subprocess.Popen(
[sys.executable, '-c',
textwrap.dedent("""
import subprocess, sys
subprocess.Popen([sys.executable, {fd_status!r}] +
[str(x) for x in range({max_fd})],
close_fds=True)
""".format(fd_status=fd_status, max_fd=max_fd_open+1))],
stdout=subprocess.PIPE, close_fds=False)
finally:
resource.setrlimit(resource.RLIMIT_NOFILE, (rlim_cur, rlim_max))
output, unused_stderr = p.communicate()
remaining_fds = set(map(int, output.strip().split(b',')))
self.assertFalse(remaining_fds & open_fds,
msg="Some fds were left open.")
# Mac OS X Tiger (10.4) has a kernel bug: sometimes, the file
# descriptor of a pipe closed in the parent process is valid in the
# child process according to fstat(), but the mode of the file

5
Misc/NEWS
View File

@ -18,6 +18,11 @@ Core and Builtins
Library
-------
- Issue #21618: The subprocess module could fail to close open fds that were
inherited by the calling process and already higher than POSIX resource
limits would otherwise allow. On systems with a functioning /proc/self/fd
or /dev/fd interface the max is now ignored and all fds are closed.
- Issue #21552: Fixed possible integer overflow of too long string lengths in
the tkinter module on 64-bit platforms.

87
Modules/_posixsubprocess.c
View File

@ -44,10 +44,6 @@
#define POSIX_CALL(call) do { if ((call) == -1) goto error; } while (0)
/* Maximum file descriptor, initialized on module load. */
static long max_fd;
/* Given the gc module call gc.enable() and return 0 on success. */
static int
_enable_gc(PyObject *gc_module)
@ -166,14 +162,39 @@ make_inheritable(PyObject *py_fds_to_keep, int errpipe_write)
}
/* Close all file descriptors in the range start_fd inclusive to
* end_fd exclusive except for those in py_fds_to_keep. If the
* range defined by [start_fd, end_fd) is large this will take a
* long time as it calls close() on EVERY possible fd.
/* 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
#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(int start_fd, int end_fd, PyObject *py_fds_to_keep)
_close_fds_by_brute_force(long start_fd, PyObject *py_fds_to_keep)
{
long end_fd = safe_get_max_fd();
Py_ssize_t num_fds_to_keep = PySequence_Length(py_fds_to_keep);
Py_ssize_t keep_seq_idx;
int fd_num;
@ -229,16 +250,14 @@ struct linux_dirent64 {
* it with some cpp #define magic to work on other OSes as well if you want.
*/
static void
_close_open_fd_range_safe(int start_fd, int end_fd, PyObject* py_fds_to_keep)
_close_open_fds_safe(int start_fd, PyObject* py_fds_to_keep)
{
int fd_dir_fd;
if (start_fd >= end_fd)
return;
fd_dir_fd = _Py_open(FD_DIR, O_RDONLY);
if (fd_dir_fd == -1) {
/* No way to get a list of open fds. */
_close_fds_by_brute_force(start_fd, end_fd, py_fds_to_keep);
_close_fds_by_brute_force(start_fd, py_fds_to_keep);
return;
} else {
char buffer[sizeof(struct linux_dirent64)];
@ -253,23 +272,23 @@ _close_open_fd_range_safe(int start_fd, int end_fd, PyObject* py_fds_to_keep)
entry = (struct linux_dirent64 *)(buffer + offset);
if ((fd = _pos_int_from_ascii(entry->d_name)) < 0)
continue; /* Not a number. */
if (fd != fd_dir_fd && fd >= start_fd && fd < end_fd &&
if (fd != fd_dir_fd && fd >= start_fd &&
!_is_fd_in_sorted_fd_sequence(fd, py_fds_to_keep)) {
while (close(fd) < 0 && errno == EINTR);
}
}
}
close(fd_dir_fd);
while (close(fd_dir_fd) < 0 && errno == EINTR);
}
}
#define _close_open_fd_range _close_open_fd_range_safe
#define _close_open_fds _close_open_fds_safe
#else /* NOT (defined(__linux__) && defined(HAVE_SYS_SYSCALL_H)) */
/* Close all open file descriptors in the range start_fd inclusive to end_fd
* exclusive. Do not close any in the sorted py_fds_to_keep list.
/* Close all open file descriptors from start_fd and higher.
* Do not close any in the sorted py_fds_to_keep list.
*
* This function violates the strict use of async signal safe functions. :(
* It calls opendir(), readdir() and closedir(). Of these, the one most
@ -282,17 +301,13 @@ _close_open_fd_range_safe(int start_fd, int end_fd, PyObject* py_fds_to_keep)
* http://womble.decadent.org.uk/readdir_r-advisory.html
*/
static void
_close_open_fd_range_maybe_unsafe(int start_fd, int end_fd,
PyObject* py_fds_to_keep)
_close_open_fds_maybe_unsafe(long start_fd, PyObject* py_fds_to_keep)
{
DIR *proc_fd_dir;
#ifndef HAVE_DIRFD
while (_is_fd_in_sorted_fd_sequence(start_fd, py_fds_to_keep) &&
(start_fd < end_fd)) {
while (_is_fd_in_sorted_fd_sequence(start_fd, py_fds_to_keep)) {
++start_fd;
}
if (start_fd >= end_fd)
return;
/* 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
@ -300,8 +315,6 @@ _close_open_fd_range_maybe_unsafe(int start_fd, int end_fd,
while (close(start_fd) < 0 && errno == EINTR);
++start_fd;
#endif
if (start_fd >= end_fd)
return;
#if defined(__FreeBSD__)
if (!_is_fdescfs_mounted_on_dev_fd())
@ -311,7 +324,7 @@ _close_open_fd_range_maybe_unsafe(int start_fd, int end_fd,
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, end_fd, py_fds_to_keep);
_close_fds_by_brute_force(start_fd, py_fds_to_keep);
} else {
struct dirent *dir_entry;
#ifdef HAVE_DIRFD
@ -324,7 +337,7 @@ _close_open_fd_range_maybe_unsafe(int start_fd, int end_fd,
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 && fd < end_fd &&
if (fd != fd_used_by_opendir && fd >= start_fd &&
!_is_fd_in_sorted_fd_sequence(fd, py_fds_to_keep)) {
while (close(fd) < 0 && errno == EINTR);
}
@ -332,13 +345,13 @@ _close_open_fd_range_maybe_unsafe(int start_fd, int end_fd,
}
if (errno) {
/* readdir error, revert behavior. Highly Unlikely. */
_close_fds_by_brute_force(start_fd, end_fd, py_fds_to_keep);
_close_fds_by_brute_force(start_fd, py_fds_to_keep);
}
closedir(proc_fd_dir);
}
}
#define _close_open_fd_range _close_open_fd_range_maybe_unsafe
#define _close_open_fds _close_open_fds_maybe_unsafe
#endif /* else NOT (defined(__linux__) && defined(HAVE_SYS_SYSCALL_H)) */
@ -457,14 +470,8 @@ child_exec(char *const exec_array[],
/* close FDs after executing preexec_fn, which might open FDs */
if (close_fds) {
int local_max_fd = max_fd;
#if defined(__NetBSD__)
local_max_fd = fcntl(0, F_MAXFD);
if (local_max_fd < 0)
local_max_fd = max_fd;
#endif
/* TODO HP-UX could use pstat_getproc() if anyone cares about it. */
_close_open_fd_range(3, local_max_fd, py_fds_to_keep);
_close_open_fds(3, py_fds_to_keep);
}
/* This loop matches the Lib/os.py _execvpe()'s PATH search when */
@ -759,11 +766,5 @@ static struct PyModuleDef _posixsubprocessmodule = {
PyMODINIT_FUNC
PyInit__posixsubprocess(void)
{
#ifdef _SC_OPEN_MAX
max_fd = sysconf(_SC_OPEN_MAX);
if (max_fd == -1)
#endif
max_fd = 256; /* Matches Lib/subprocess.py */
return PyModule_Create(&_posixsubprocessmodule);
}