Support long PATH values in erlexec

[HoloRin]

Previously a finite 10240 buffer was used. Long paths can fail semi-silently, while long paths that already contain the erlang bindir at the end can cause a crash.

Reproducible with the following bash script:

#!/usr/bin/env bash
set -euo pipefail

ERL_PATH="$(erl -eval 'io:format("~s~n", [os:getenv("PATH")])' -s init stop -noshell)"

IFS=':' read -ra ERL_PATH_COMPONENTS <<< "$ERL_PATH"

BINDIR="${ERL_PATH_COMPONENTS[0]}"
OTHER_DIR="${ERL_PATH_COMPONENTS[1]}"

while [ ${#PATH} -lt 10240 ]; do
    PATH="${PATH}:${OTHER_DIR}"
done
PATH="${PATH}:${PATH}:${BINDIR}"

erl -eval 'io:format("hello~n", [])' -s init stop -noshell

Output:

% ./repro.sh
./repro.sh: line 19: 98643 Bus error: 10           erl -eval 'io:format("hello~n", [])' -s init stop -noshell

[github-actions]

CT Test Results

    3 files    143 suites   49m 0s ⏱️
1 598 tests 1 549 ✅ 49 💤 0 ❌
2 342 runs  2 268 ✅ 74 💤 0 ❌

Results for commit 9ac7bcf.

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// Erlang/OTP Github Action Bot

[garazdawi]

Hello! Thanks for the fix! Can you add a test to https://github.com/erlang/otp/blob/master/erts/test/erlexec_SUITE.erl ?

[HoloRin]

@garazdawi how do I run just erlexec_SUITE? I am getting a hard crash of my whole macbook when I run cd erts && make test

[garazdawi]

Try make system_test ARGS="-suite erlexec_SUITE" from the top. There are more indepth descriptions here: https://github.com/erlang/otp/blob/master/HOWTO/TESTING.md

[ericmj]

@garazdawi We added some test cases for long PATHs and various combinations of the bin directory location in the PATH.

[garazdawi]

Great! Thanks! Putting into testing over the weekend.

[jhogberg]

erlexec_SUITE:long_path_env/1 goes sideways on all tested platforms, failing on line 457:

  447: long_path_env(Config) when is_list(Config) ->
  448:     OriginalPath = os:getenv("PATH"),
  449:     [BinPath, RestPath] = string:split(OriginalPath, ":"),
  450:     LongPath = lists:duplicate(10240, "x"),
  451:     ExpectedPath = OriginalPath ++ ":" ++ LongPath,
  452:     {ok, [[PName]]} = init:get_argument(progname),
  453:     Cmd = PName ++ " -noshell -eval 'io:format(\"~ts\", [os:getenv(\"PATH\")]),erlang:halt()'",
  454: 
  455:     os:putenv("PATH", OriginalPath ++ ":" ++ LongPath ++ ":" ++ BinPath),
  456:     Output1 = os:cmd(Cmd),
  457:     true = string:equal(ExpectedPath, Output1),
  458: 
  459:     os:putenv("PATH", ExpectedPath),
  460:     Output2 = os:cmd(Cmd),
  461:     true = string:equal(ExpectedPath, Output2),
  462: 
  463:     os:putenv("PATH", RestPath ++ ":" ++ LongPath),
  464:     Output3 = os:cmd(Cmd),
  465:     true = string:equal(ExpectedPath, Output3),
  466: 
  467:     ok.

[garazdawi]

The test assumes that the BinPath is the first segment of the PATH, but it does not have to be. Not sure we have a function to locate which path segment an executable is located in...

[HoloRin]

The test assumes that the BinPath is the first segment of the PATH, but it does not have to be. Not sure we have a function to locate which path segment an executable is located in...

Our understanding of the code existing behavior in erlexec is that the BinPath prepended to the PATH, and any duplicates found later in the path are dropped. In the test, this has already happened once, so BinPath is at the head of the PATH. However, I suppose that leaves open a possibility of an implementation passing this test where that's not actually the case. We can strengthen the test.

[garazdawi]

I don't know why, but when running tests through ts (Which is used by all our interal tests, but not by github actions) the current test is passed as the first argument in the path. Something like this:

erl -env PATH "/ldisk/daily_build/28_master-opu_o.2025-01-26_21/test/emulator_test:/ldisk/daily_build/28_master-opu_o.2025-01-26_21/otp/lib/erlang/erts-16.0/bin:/"

which makes the "emulator_test" be the first in the path. You should be able to reproduce it like this:

export ERL_TOP=`pwd`
./otp_build -a
make release_tests
cd release/tests/test_server
PATH=$ERL_TOP/bin/:$PATH erl -noshell -eval 'ts:install(), ts:run(system, erlexec_SUITE, long_path_env, [batch]).' -s init stop

[ericmj]

We removed the trailing the PATHSEP here since the PATH should never end with : afaik.

[ericmj]

@garazdawi Thanks for giving us a to reproduce the error. Since ts sets a different a PATH it's hard to write tests for both ts and make system_test but we have done a best effort.

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