| msg307962 - (view) |
Author: Alexey Izbyshev (izbyshev) *  |
Date: 2017-12-10 17:14 |
| Demonstration: $ cat test.py import os import subprocess import sys fd = os.dup(sys.stdout.fileno()) subprocess.call([sys.executable, '-c', 'import sys;' 'print("Hello stdout");' 'print("Hello fd", file=open(int(sys.argv[1]), "w"))', str(fd)], stdout=fd, pass_fds=[fd]) $ python3 test.py Hello stdout Traceback (most recent call last): File "", line 1, in OSError: [Errno 9] Bad file descriptor I see two issues here: 1. The fact that file descriptors specified for redirection are closed (even with close_fds=False) unless in range [0, 2] is not documented and not tested. If I change the corresponding code in _posixsubprocess.c to close them only if they are ends of pipes created by subprocess itself, all tests still pass. Also, shells behave differently: e.g., in command 'echo 3>&1' fd 3 is duplicated but not closed in the child, so subprocess behavior may be not what people expect. 2. pass_fds interaction with (1) should be fixed and documented. We may either raise ValueError if pass_fds contains a redirected fd or don't close such a redirected fd. Please provide your thoughts. |
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| msg307967 - (view) |
Author: Antoine Pitrou (pitrou) *  |
Date: 2017-12-10 18:38 |
| Thanks for the report and the investigation! > 1. The fact that file descriptors specified for redirection are closed (even with close_fds=False) unless in range [0, 2] is not documented and not tested. That sounds like a bug to me, so we should fix it if decently possible. > 2. pass_fds interaction with (1) should be fixed and documented. We may either raise ValueError if pass_fds contains a redirected fd or don't close such a redirected fd. Same here, it seems like a bug which deserves fixing. Do you want to submit a PR for this? |
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| msg307995 - (view) |
Author: Alexey Izbyshev (izbyshev) * |
Date: 2017-12-10 22:03 |
| Regarding fixing (1), I'm worrying about backward compatibility a bit. Some people who discovered that behavior might rely on such "move" semantics and expect that the redirected descriptor is not leaked into the child. OTOH, since descriptors are non-inheritable by default since 3.4, it might be less of an issue now. What do you think? Otherwise, yes, I'd like to fix this, but fixing is a bit trickier than it may seem because sometimes descriptors are duplicated in _posixsubprocess.c (in case of low fds), so we need to track the ownership properly. I've already performed some work and discovered another issue: in a corner case involving closed standard fds, pipes created by subprocess may leak into the child and/or an incorrect redirection may occur. Since I can't completely fix this issue without affecting a discovered one, I think I'll do the opposite: file a new issue, fix it, and then go back to this one. |
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| msg308173 - (view) |
Author: Antoine Pitrou (pitrou) * |
Date: 2017-12-12 23:38 |
| > Regarding fixing (1), I'm worrying about backward compatibility a bit. Well, people shouldn't rely on bugs. Otherwise we would never be able to fix bugs, lest someone relies on it. |
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| msg314426 - (view) |
Author: Gregory P. Smith (gregory.p.smith) * |
Date: 2018-03-25 19:01 |
| This bug stems from: https://github.com/python/cpython/blob/master/Modules/_posixsubprocess.c#L454 When stdout=fd is passed, that results in c2pwrite=fd. The stdin/stdout/stderr pipe fds are closed when > 2 without checking to see if they are listed in pass_fds. https://github.com/python/cpython/blob/master/Lib/subprocess.py#L1306 maps the following: stdin -> p2cread stdout -> c2pwrite stderr -> errwrite |
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| msg314428 - (view) |
Author: Alexey Izbyshev (izbyshev) * |
Date: 2018-03-25 19:12 |
| Actually I've started to work on this with #32844, but got no feedback. This issue may of course be fixed independently, but the problems with descriptor ownership for fds <= 2 will remain unless all ownership problems are fixed at once. |
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| msg315202 - (view) |
Author: Alexey Izbyshev (izbyshev) * |
Date: 2018-04-11 22:06 |
| An alternative fix is here: https://github.com/izbyshev/cpython/commit/b89b52f28490b69142d5c061604b3a3989cec66c Feel free to use the test if you don't like the approach :) |
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| msg324968 - (view) |
Author: Gregory P. Smith (gregory.p.smith) * |
Date: 2018-09-11 00:46 |
| New changeset ce34410b8b67f49d8275c05d51b3ead50cf97f48 by Gregory P. Smith in branch 'master': bpo-32270: Don't close stdin/out/err in pass_fds (GH-6242) https://github.com/python/cpython/commit/ce34410b8b67f49d8275c05d51b3ead50cf97f48 |
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| msg324980 - (view) |
Author: Gregory P. Smith (gregory.p.smith) * |
Date: 2018-09-11 04:36 |
| New changeset 9c4a63fc17efea31ad41f90d28825be37469e0e2 by Gregory P. Smith (Miss Islington (bot)) in branch '3.7': bpo-32270: Don't close stdin/out/err in pass_fds (GH-6242) (GH-9148) https://github.com/python/cpython/commit/9c4a63fc17efea31ad41f90d28825be37469e0e2 |
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| msg324992 - (view) |
Author: Gregory P. Smith (gregory.p.smith) * |
Date: 2018-09-11 06:00 |
| New changeset 2173bb818c6c726d831b106ed0d3fad7825905dc by Gregory P. Smith (Miss Islington (bot)) in branch '3.6': bpo-32270: Don't close stdin/out/err in pass_fds (GH-6242) (GH-9149) https://github.com/python/cpython/commit/2173bb818c6c726d831b106ed0d3fad7825905dc |
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| msg325087 - (view) |
Author: Alexey Izbyshev (izbyshev) * |
Date: 2018-09-11 22:52 |
| Thank you, Gregory! |
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