| msg227582 - (view) |
Author: Nikolaus Rath (nikratio) * |
Date: 2014-09-26 01:24 |
| I received a bugreport due to a crash when calling SSLObject.send(). The traceback ends with: [...] File "/usr/local/lib/python3.4/dist-packages/dugong-3.2-py3.4.egg/dugong/__init__.py", line 584, in _co_send len_ = self._sock.send(buf) File "/usr/lib/python3.4/ssl.py", line 679, in send v = self._sslobj.write(data) ssl.SSLError: [SSL: BAD_WRITE_RETRY] bad write retry (_ssl.c:1636) At first I thought that this is an exception that my application should catch and handle. However, when trying to figure out what exactly BAD_WRITE_RETRY means I get the impression that the fault is actually in Python's _ssl.c. The only places where this error is returned by OpenSSL are ssl/s2_pkt.c:480 and ssl/s3_pkt.c:1179, and in each case the problem seems to be with the caller supplying an invalid buffer after an initial write request failed to complete due to non-blocking IO. This does not seem to be something that could be caused by whatever Python code, so I think there is a problem in _ssl.c. |
|
|
| msg227583 - (view) |
Author: Antoine Pitrou (pitrou) *  |
Date: 2014-09-26 02:06 |
| Hmm... this sounds like , except that it should be fixed in 3.4... |
|
|
| msg254343 - (view) |
Author: Nikolaus Rath (nikratio) * |
Date: 2015-11-08 15:39 |
| This just happened again to someone else, also using Python 3.4: https://bitbucket.org/nikratio/s3ql/issues/87 Is there anything the affected people can do to help debugging this? |
|
|
| msg254389 - (view) |
Author: Stefan Krah (skrah) * |
Date: 2015-11-09 14:28 |
| I had a similar issue with ucspi-ssl that was fixed by following the O'Reilly book's recommendations w.r.t WANT_READ/WANT_WRITE with non-blocking sockets to the letter. The recommendations are quite complex since apparently WANT_READ/WANT_WRITE mean different things depending on whether they occur *during a read* or *during a write*. I haven't used Python's SSL module much: Since those flags are exposed on the Python level, are users supposed to take care of the above issues themselves for non-blocking sockets? |
|
|
| msg257350 - (view) |
Author: Nikolaus Rath (nikratio) * |
Date: 2016-01-02 17:45 |
| *ping* Just letting people know that this is still happening regularly and still present in 3.5. Some reports: https://bitbucket.org/nikratio/s3ql/issues/87/ https://bitbucket.org/nikratio/s3ql/issues/109/ (last comment) |
|
|
| msg257413 - (view) |
Author: Stefan Krah (skrah) * |
Date: 2016-01-03 13:08 |
| As I said in , the read/write handling for non-blocking sockets is far from trivial. I'm not sure that this is a Python bug: Looking at dugong/__init__.py, I don't think this implements the recommendations in the OpenSSL book that I mentioned. The book recommends to keep a state ... struct iostate { int read_waiton_write; int read_waiton_read; int write_waiton_write; int write_waiton_read; int can_read; int can_write; }; ... a check_availability() function that sets 'can_read', 'can_write' ... a write_allowed() function that determines whether a write is even possible to attempt ... int write_allowed(struct iostate *state) { if (state->read_waiton_write | |
state->read_waiton_read) return 0; if (state->can_write) return 1; if (state->can_read && state->write_waiton_read) return 1; return 0; } ... and finally, the glorious loop: while (!done) { while (check_availability(ssl, &state) == -1 |
|
| msg257535 - (view) |
Author: Nikolaus Rath (nikratio) * |
Date: 2016-01-05 17:33 |
| Stefan, sorry for ignoring your earlier reply. I somehow missed the question at the end. I believe that users of the Python module are *not* expected to make use of the WANT_READ, WANT_WRITE flags. Firstly because the documentation (of Python's ssl module) doesn't say anything about that, and secondly because the code that's necessary to handle these flags is a prime example for complexity that is imposed by the C API that should be hidden to Python users. That said, could you give a more specific reference to the O'Relly book (and maybe even page or chapter)? At the moment it's a little hard for me to follow the rest of your message. Essentially, if I'm trying to write to a non-blocking, Python SSL socket, I would expect that this either succeeds or raises SSL_WANT_WRITE/READ. Not having read the book, it seems to me this is the only information that's useful to a Python caller. In what situation would you need the more exact state that your C example tracks? |
|
|
| msg257562 - (view) |
Author: Stefan Krah (skrah) * |
Date: 2016-01-05 22:33 |
| https://books.google.com/books?id=IIqwAy4qEl0C&redir_esc=y , page 159 ff. Modules/_ssl.c:_ssl__SSLSocket_write_impl() just raises PySSLWantReadError etc. if the socket is non-blocking. IOW, it's a thin wrapper around SSL_write(). So yes, I think you do need complete error handling on the Python level. |
|
|
| msg257614 - (view) |
Author: Nikolaus Rath (nikratio) * |
Date: 2016-01-06 17:06 |
| Would you be willing to review a patch to incorporate the handling into the SSL module? |
|
|