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author | Samuel Merritt <sam@swiftstack.com> | 2015-12-08 16:36:05 -0800 |
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committer | John Dickinson <me@not.mn> | 2016-01-20 06:55:43 -0800 |
commit | a4c1825a026655b7ed21d779824ae7c25318fd52 (patch) | |
tree | 45e1236a025f28c448a20ab93242f9a61545c33c | |
parent | 036c2f348d24c01c7a4deba3e44889c45270b46d (diff) | |
download | swift-a4c1825a026655b7ed21d779824ae7c25318fd52.tar.gz |
Fix memory/socket leak in proxy on truncated SLO/DLO GET
When a client disconnected while consuming an SLO or DLO GET response,
the proxy would leak a socket. This could be observed via strace as a
socket that had shutdown() called on it, but was never closed. It
could also be observed by counting entries in /proc/<pid>/fd, where
<pid> is the pid of a proxy server worker process.
This is due to a memory leak in SegmentedIterable. A SegmentedIterable
has an 'app_iter' attribute, which is a generator. That generator
references 'self' (the SegmentedIterable object). This creates a
cyclic reference: the generator refers to the SegmentedIterable, and
the SegmentedIterable refers to the generator.
Python can normally handle cyclic garbage; reference counting won't
reclaim it, but the garbage collector will. However, objects with
finalizers will stop the garbage collector from collecting them* and
the cycle of which they are part.
For most objects, "has finalizer" is synonymous with "has a __del__
method". However, a generator has a finalizer once it's started
running and before it finishes: basically, while it has stack frames
associated with it**.
When a client disconnects mid-stream, we get a memory leak. We have
our SegmentedIterable object (call it "si"), and its associated
generator. si.app_iter is the generator, and the generator closes over
si, so we have a cycle; and the generator has started but not yet
finished, so the generator needs finalization; hence, the garbage
collector won't ever clean it up.
The socket leak comes in because the generator *also* refers to the
request's WSGI environment, which contains wsgi.input, which
ultimately refers to a _socket object from the standard
library. Python's _socket objects only close their underlying file
descriptor when their reference counts fall to 0***.
This commit makes SegmentedIterable.close() call
self.app_iter.close(), thereby unwinding its generator's stack and
making it eligible for garbage collection.
* in Python < 3.4, at least. See PEP 442.
** see PyGen_NeedsFinalizing() in Objects/genobject.c and also
has_finalizer() in Modules/gcmodule.c in Python.
*** see sock_dealloc() in Modules/socketmodule.c in Python. See
sock_close() in the same file for the other half of the sad story.
This closes CVE-2016-0738.
Closes-Bug: 1493303
Change-Id: I9b617bfc152dca40d1750131d1d814d85c0a88dd
Co-Authored-By: Kota Tsuyuzaki <tsuyuzaki.kota@lab.ntt.co.jp>
-rw-r--r-- | swift/common/request_helpers.py | 6 | ||||
-rw-r--r-- | test/unit/common/middleware/test_slo.py | 62 |
2 files changed, 66 insertions, 2 deletions
diff --git a/swift/common/request_helpers.py b/swift/common/request_helpers.py index 8aa8457e4..611ee8380 100644 --- a/swift/common/request_helpers.py +++ b/swift/common/request_helpers.py @@ -378,6 +378,9 @@ class SegmentedIterable(object): self.logger.exception(_('ERROR: An error occurred ' 'while retrieving segments')) raise + finally: + if self.current_resp: + close_if_possible(self.current_resp.app_iter) def app_iter_range(self, *a, **kw): """ @@ -420,5 +423,4 @@ class SegmentedIterable(object): Called when the client disconnect. Ensure that the connection to the backend server is closed. """ - if self.current_resp: - close_if_possible(self.current_resp.app_iter) + close_if_possible(self.app_iter) diff --git a/test/unit/common/middleware/test_slo.py b/test/unit/common/middleware/test_slo.py index 4d483c87c..8119b5fb7 100644 --- a/test/unit/common/middleware/test_slo.py +++ b/test/unit/common/middleware/test_slo.py @@ -1253,6 +1253,68 @@ class TestSloGetManifest(SloTestCase): self.assertEqual(headers['X-Object-Meta-Fish'], 'Bass') self.assertEqual(body, '') + def test_generator_closure(self): + # Test that the SLO WSGI iterable closes its internal .app_iter when + # it receives a close() message. + # + # This is sufficient to fix a memory leak. The memory leak arises + # due to cyclic references involving a running generator; a running + # generator sometimes preventes the GC from collecting it in the + # same way that an object with a defined __del__ does. + # + # There are other ways to break the cycle and fix the memory leak as + # well; calling .close() on the generator is sufficient, but not + # necessary. However, having this test is better than nothing for + # preventing regressions. + leaks = [0] + + class LeakTracker(object): + def __init__(self, inner_iter): + leaks[0] += 1 + self.inner_iter = iter(inner_iter) + + def __iter__(self): + return self + + def next(self): + return next(self.inner_iter) + + def close(self): + leaks[0] -= 1 + self.inner_iter.close() + + class LeakTrackingSegmentedIterable(slo.SegmentedIterable): + def _internal_iter(self, *a, **kw): + it = super( + LeakTrackingSegmentedIterable, self)._internal_iter( + *a, **kw) + return LeakTracker(it) + + status = [None] + headers = [None] + + def start_response(s, h, ei=None): + status[0] = s + headers[0] = h + + req = Request.blank( + '/v1/AUTH_test/gettest/manifest-abcd', + environ={'REQUEST_METHOD': 'GET', + 'HTTP_ACCEPT': 'application/json'}) + + # can't self.call_slo() here since we don't want to consume the + # whole body + with patch.object(slo, 'SegmentedIterable', + LeakTrackingSegmentedIterable): + app_resp = self.slo(req.environ, start_response) + self.assertEqual(status[0], '200 OK') # sanity check + body_iter = iter(app_resp) + chunk = next(body_iter) + self.assertEqual(chunk, 'aaaaa') # sanity check + + app_resp.close() + self.assertEqual(0, leaks[0]) + def test_head_manifest_is_efficient(self): req = Request.blank( '/v1/AUTH_test/gettest/manifest-abcd', |