#4489: Fix usage of fd-based functions to new api introduced earlier today

Also add an explicit test for safe implementation usage on supported platforms.

As a side effect, this commit adds a module-level attribute 'rmtree_is_safe'
which offers introspection whether the current rmtree implementation is safe
against symlink attacks.
This commit is contained in:
Hynek Schlawack 2012-06-23 20:28:32 +02:00
parent 1641cea02b
commit 2100b42317
3 changed files with 44 additions and 17 deletions

View File

@ -195,9 +195,9 @@ Directory and files operations
The default :func:`rmtree` function is susceptible to a symlink attack:
given proper timing and circumstances, attackers can use it to delete
files they wouldn't be able to access otherwise. Thus -- on platforms
that support the necessary fd-based functions :func:`os.openat` and
:func:`os.unlinkat` -- a safe version of :func:`rmtree` is used, which
isn't vulnerable.
that support the necessary fd-based functions -- a safe version of
:func:`rmtree` is used, which isn't vulnerable. In this case
:data:`rmtree_is_safe` is set to True.
If *onerror* is provided, it must be a callable that accepts three
parameters: *function*, *path*, and *excinfo*.
@ -210,8 +210,15 @@ Directory and files operations
.. versionchanged:: 3.3
Added a safe version that is used automatically if platform supports
the fd-based functions :func:`os.openat` and :func:`os.unlinkat`.
fd-based functions.
.. data:: rmtree_is_safe
Indicates whether the current platform and implementation has a symlink
attack-proof version of :func:`rmtree`. Currently this is only true for
platforms supporting fd-based directory access functions.
.. versionadded:: 3.3
.. function:: move(src, dst)

View File

@ -362,9 +362,9 @@ def _rmtree_unsafe(path, onerror):
_rmtree_unsafe(fullname, onerror)
else:
try:
os.remove(fullname)
os.unlink(fullname)
except os.error:
onerror(os.remove, fullname, sys.exc_info())
onerror(os.unlink, fullname, sys.exc_info())
try:
os.rmdir(path)
except os.error:
@ -374,21 +374,21 @@ def _rmtree_unsafe(path, onerror):
def _rmtree_safe_fd(topfd, path, onerror):
names = []
try:
names = os.flistdir(topfd)
names = os.listdir(topfd)
except os.error:
onerror(os.flistdir, path, sys.exc_info())
onerror(os.listdir, path, sys.exc_info())
for name in names:
fullname = os.path.join(path, name)
try:
orig_st = os.fstatat(topfd, name)
orig_st = os.stat(name, dir_fd=topfd)
mode = orig_st.st_mode
except os.error:
mode = 0
if stat.S_ISDIR(mode):
try:
dirfd = os.openat(topfd, name, os.O_RDONLY)
dirfd = os.open(name, os.O_RDONLY, dir_fd=topfd)
except os.error:
onerror(os.openat, fullname, sys.exc_info())
onerror(os.open, fullname, sys.exc_info())
else:
try:
if os.path.samestat(orig_st, os.fstat(dirfd)):
@ -397,21 +397,22 @@ def _rmtree_safe_fd(topfd, path, onerror):
os.close(dirfd)
else:
try:
os.unlinkat(topfd, name)
os.unlink(name, dir_fd=topfd)
except os.error:
onerror(os.unlinkat, fullname, sys.exc_info())
onerror(os.unlink, fullname, sys.exc_info())
try:
os.rmdir(path)
except os.error:
onerror(os.rmdir, path, sys.exc_info())
_use_fd_functions = hasattr(os, 'openat') and hasattr(os, 'unlinkat')
rmtree_is_safe = _use_fd_functions = (os.unlink in os.supports_dir_fd and
os.open in os.supports_dir_fd)
def rmtree(path, ignore_errors=False, onerror=None):
"""Recursively delete a directory tree.
If ignore_errors is set, errors are ignored; otherwise, if onerror
is set, it is called to handle the error with arguments (func,
path, exc_info) where func is os.listdir, os.remove, or os.rmdir;
path, exc_info) where func is platform and implementation dependent;
path is the argument to that function that caused it to fail; and
exc_info is a tuple returned by sys.exc_info(). If ignore_errors
is false and onerror is None, an exception is raised.

View File

@ -159,8 +159,7 @@ class TestShutil(unittest.TestCase):
# at os.listdir. The first failure may legally
# be either.
if 0 <= self.errorState < 2:
if (func is os.remove or
hasattr(os, 'unlinkat') and func is os.unlinkat):
if func is os.unlink:
self.assertIn(arg, [self.child_file_path, self.child_dir_path])
else:
if self.errorState == 1:
@ -486,6 +485,26 @@ class TestShutil(unittest.TestCase):
shutil.copyfile(link, dst)
self.assertFalse(os.path.islink(dst))
def test_rmtree_uses_safe_fd_version_if_available(self):
if os.unlink in os.supports_dir_fd and os.open in os.supports_dir_fd:
self.assertTrue(shutil._use_fd_functions)
self.assertTrue(shutil.rmtree_is_safe)
tmp_dir = self.mkdtemp()
d = os.path.join(tmp_dir, 'a')
os.mkdir(d)
try:
real_rmtree = shutil._rmtree_safe_fd
class Called(Exception): pass
def _raiser(*args, **kwargs):
raise Called
shutil._rmtree_safe_fd = _raiser
self.assertRaises(Called, shutil.rmtree, d)
finally:
shutil._rmtree_safe_fd = real_rmtree
else:
self.assertFalse(shutil._use_fd_functions)
self.assertFalse(shutil.rmtree_is_safe)
def test_rmtree_dont_delete_file(self):
# When called on a file instead of a directory, don't delete it.
handle, path = tempfile.mkstemp()