Isolated mode doesn't ignore PYTHONHASHSEED

[ncoghlan]

BPO	26122
Nosy	@ncoghlan, @vstinner, @tiran

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2019-05-15.02:23:01.835>
created_at = <Date 2016-01-15.12:48:14.717>
labels = ['interpreter-core', '3.8', 'type-bug', '3.7']
title = "Isolated mode doesn't ignore PYTHONHASHSEED"
updated_at = <Date 2019-05-20.15:32:22.337>
user = 'https://github.com/ncoghlan'

bugs.python.org fields:

activity = <Date 2019-05-20.15:32:22.337>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2019-05-15.02:23:01.835>
closer = 'vstinner'
components = ['Interpreter Core']
creation = <Date 2016-01-15.12:48:14.717>
creator = 'ncoghlan'
dependencies = []
files = []
hgrepos = []
issue_num = 26122
keywords = []
message_count = 4.0
messages = ['258290', '342533', '342553', '342919']
nosy_count = 3.0
nosy_names = ['ncoghlan', 'vstinner', 'christian.heimes']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue26122'
versions = ['Python 3.7', 'Python 3.8']

[ncoghlan]

While working on the draft PEP-432 implementation, I noticed that -I isn't special cased for early processing the same way that -E is: https://hg.python.org/cpython/file/tip/Modules/main.c#l265

This means that when isolated mode is used to turn off environment variable access, PYTHONHASHSEED may still be read while configuring hash randomisation.

[vstinner]

This issue has been fixed in Python 3.8 with my work on refactoring Py_Main(). -E and -I command line options are now parsed, before reading PYTHONHASHSEED, and -I imply -E as expected. Extract of the code:

    if (config->isolated > 0) {
        config->user_site_directory = 0;
    }

    if (config->use_environment) {
        err = config_read_env_vars(config);
        if (_Py_INIT_FAILED(err)) {
            return err;
        }
    }

where config_read_env_vars() indirectly reads PYTHONHASHSEED.

I'm not sure if the issue is fixed in Python 3.7 or not. The code in Python 3.7 was in a bad state. It's getting better with Python 3.8 :-)

Note: the overall refactoring work is related to PEP-432 and PEP-587.

[tiran]

Is there a way to fix the issue in 3.7 and earlier? We might consider it a security issue.

[vstinner]

Is there a way to fix the issue in 3.7 and earlier? We might consider it a security issue.

Hum, Python 3.7 is fixed as well. At least, in the 3.7 dev branch.

Fixed seed:

vstinner@apu$ PYTHONHASHSEED=42 ./python -c 'print(set("abcdefgh"))'
{'g', 'e', 'a', 'b', 'c', 'f', 'h', 'd'}
vstinner@apu$ PYTHONHASHSEED=42 ./python -c 'print(set("abcdefgh"))'
{'g', 'e', 'a', 'b', 'c', 'f', 'h', 'd'}
vstinner@apu$ PYTHONHASHSEED=42 ./python -c 'print(set("abcdefgh"))'
{'g', 'e', 'a', 'b', 'c', 'f', 'h', 'd'}
vstinner@apu$ PYTHONHASHSEED=42 ./python -c 'print(set("abcdefgh"))'
{'g', 'e', 'a', 'b', 'c', 'f', 'h', 'd'}

Random seed:

vstinner@apu$ PYTHONHASHSEED=42 ./python -I -c 'print(set("abcdefgh"))'
{'b', 'e', 'd', 'f', 'g', 'c', 'a', 'h'}
vstinner@apu$ PYTHONHASHSEED=42 ./python -I -c 'print(set("abcdefgh"))'
{'d', 'g', 'e', 'b', 'h', 'f', 'a', 'c'}
vstinner@apu$ PYTHONHASHSEED=42 ./python -I -c 'print(set("abcdefgh"))'
{'e', 'b', 'g', 'c', 'a', 'h', 'f', 'd'}
vstinner@apu$ PYTHONHASHSEED=42 ./python -I -c 'print(set("abcdefgh"))'
{'c', 'd', 'a', 'g', 'f', 'e', 'h', 'b'}

--

Python 3.6 has the bug:

vstinner@apu$ PYTHONHASHSEED=42 python3.6 -c 'print(set("abcdefgh"))'
{'g', 'e', 'a', 'b', 'c', 'f', 'h', 'd'}
vstinner@apu$ PYTHONHASHSEED=42 python3.6 -c 'print(set("abcdefgh"))'
{'g', 'e', 'a', 'b', 'c', 'f', 'h', 'd'}
vstinner@apu$ PYTHONHASHSEED=42 python3.6 -c 'print(set("abcdefgh"))'
{'g', 'e', 'a', 'b', 'c', 'f', 'h', 'd'}
vstinner@apu$ PYTHONHASHSEED=42 python3.6 -c 'print(set("abcdefgh"))'
{'g', 'e', 'a', 'b', 'c', 'f', 'h', 'd'}

vstinner@apu$ PYTHONHASHSEED=42 python3.6 -I -c 'print(set("abcdefgh"))'
{'g', 'e', 'a', 'b', 'c', 'f', 'h', 'd'}
vstinner@apu$ PYTHONHASHSEED=42 python3.6 -I -c 'print(set("abcdefgh"))'
{'g', 'e', 'a', 'b', 'c', 'f', 'h', 'd'}
vstinner@apu$ PYTHONHASHSEED=42 python3.6 -I -c 'print(set("abcdefgh"))'
{'g', 'e', 'a', 'b', 'c', 'f', 'h', 'd'}
vstinner@apu$ PYTHONHASHSEED=42 python3.6 -I -c 'print(set("abcdefgh"))'
{'g', 'e', 'a', 'b', 'c', 'f', 'h', 'd'}