Consider deprecating and/or modifying behavior of std::env::set_var #90308

leo60228 · 2021-10-26T15:55:02Z

Observing an environment variable concurrently with a call to setenv constitutes a data race. Rust currently handles this by using a mutex, but that only protects against functions in std::env. My interpretation of POSIX (which appears to be the same as the glibc developers') is that any libc function is allowed to call getenv. This has already caused problems with getaddrinfo in #27970.
Additionally, a large amount of C code calls getenv but is otherwise thread-safe. While this isn't necessarily the standard library's issue, it's impossible for third-party libraries to soundly use this code without requiring the user to certify that this isn't an issue via an unsafe block. Some examples of this happening in practice are in time-rs/time#293 and rust-lang/flate2-rs#272.
rustsec/advisory-db#926 had several proposals on how this could be handled brought up.

Make `std::env::set_var` unsafe

This is arguably the cleanest solution to the issue. This could be considered a soundness fix, which would make it an option, but the ecosystem impact feels like it'd be too big.

Don't actually call `setenv`

std could keep track of the environment itself, and make set_var changes only visible to var and subprocesses. This is probably the way to solve the issue with the least impact on existing code, but the behavior is somewhat unexpected and not zero-cost.

Only call `setenv` in single-threaded code

This would reduce the impact further, but seems even less expected for negligible benefit.

Deprecate `std::env::set_var`

This would make it clear that setting an environment variable in the current process is discouraged. It could also be combined with not actually calling setenv, which would be my preferred solution to this issue.

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vi · 2021-10-29T15:58:50Z

Shall it be made unsafe fn, just like std::os::unix::process::CommandExt::pre_exec?

leo60228 · 2021-10-29T16:43:09Z

Shall it be made unsafe fn, just like std::os::unix::process::CommandExt::pre_exec?

The discussion in #39575 is definitely helpful here, but I don't think the same conclusions can reasonably apply to std::env::set_var.

tarcieri · 2021-10-29T16:50:49Z

Indeed. Notably they retroactively changed pre_exec to unsafe based on a justification that there weren't real-world uses of it.

That's not the case with set_var: https:/search?l=Rust&type=Code&q=set_var

I think to accomplish a similar effect, set_var would have to be deprecated, and a new unsafe fn introduced in its place (which is more or less combining options 1 & 4 proposed in the OP)

leo60228 · 2021-10-29T16:59:42Z

I think to accomplish a similar effect, set_var would have to be deprecated, and a new unsafe fn introduced in its place (which is more or less combining options 1 & 4 proposed in the OP)

That's what happened with pre_exec. before_exec is the old name.

leo60228 · 2021-11-10T17:26:42Z

For reference, .NET takes option #2.

cgwalters · 2021-11-11T18:18:57Z

Hi, there's a bunch of discussion on this issue, but I think https://internals.rust-lang.org/t/synchronized-ffi-access-to-posix-environment-variable-functions/15475 has the most information right now.

briansmith · 2022-01-04T18:55:33Z

Hi, there's a bunch of discussion on this issue, but I think https://internals.rust-lang.org/t/synchronized-ffi-access-to-posix-environment-variable-functions/15475 has the most information right now.

There is a lot of discussion in #27970 that's really about this issue. This is largely my fault because I didn't know this issue existed.

briansmith · 2022-01-04T21:55:33Z

I looked at an application that is using set_var in multiple places:

~~To provide a default value for RUST_LOG=debug when it wasn't already set. We'd prefer a way to do this without setting the environment variable.~~
To force RUST_BACKTRACE=full regardless of what the environment says. Again, we'd prefer a way to do this without setting an environment variable.
To test functions that read from the environment. At some point we should have a new solution for supporting this.
~~To do shell scripting, but in Rust. Not a big deal for us to use an unsafe function for this, though not ideal.~~ [Edit: We can use Command::{env,envs}.]

Nemo157 · 2022-01-04T22:17:36Z

To provide a default value for RUST_LOG=debug when it wasn't already set. We'd prefer a way to do this without setting the environment variable.

https://docs.rs/env_logger/latest/env_logger/struct.Env.html#method.filter_or

To force RUST_BACKTRACE=full regardless of what the environment says. Again, we'd prefer a way to do this without setting an environment variable.

#79085

EDIT: Actually, this only affects the library backtrace, the panic runtime probably does also need a in-code setter too.

leo60228 · 2022-01-04T22:24:06Z

To test functions that read from the environment. At some point we should

have a new solution for supporting this. I don't think there's a reasonable way to support this other than running that test in its own process. That's already prone to logic race conditions since tests are multithreaded. At the very least, in an integration test it should be pretty much obviously safe to put the relevant `set_env` calls at the top of `main`.

…

On Tue, Jan 4, 2022, 4:55 PM Brian Smith ***@***.***> wrote: I looked at an application that is using set_var in multiple places: - To provide a default value for RUST_LOG=debug when it wasn't already set. We'd prefer a way to do this without setting the environment variable. - To force RUST_BACKTRACE=full regardless of what the environment says. Again, we'd prefer a way to do this without setting an environment variable. - To test functions that read from the environment. At some point we should have a new solution for supporting this. - To do shell scripting, but in Rust. Not a big deal for us to use an unsafe function for this, though not ideal. — Reply to this email directly, view it on GitHub <#90308 (comment)>, or unsubscribe <https:/notifications/unsubscribe-auth/AB7X32OITRPXKVTYYIVWD7LUUNUGHANCNFSM5GYFKLHA> . Triage notifications on the go with GitHub Mobile for iOS <https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675> or Android <https://play.google.com/store/apps/details?id=com.github.android&referrer=utm_campaign%3Dnotification-email%26utm_medium%3Demail%26utm_source%3Dgithub>. You are receiving this because you authored the thread.Message ID: ***@***.***>

briansmith · 2022-01-04T22:43:58Z

First, it turns out that our use of RUST_LOG was a bit different than I described. I agree current APIs are sufficient, at least for the logging crates we use.

As far as testing goes, if the serial_test crate truly ensures no other threads are doing anything during the test, then that might work for our test uses of set_var and remove_var.

briansmith · 2022-01-04T23:47:10Z

In order to use serial_test to make set_var and remove_var in a test safe, the tests would have to be integration tests and where there are no other tests in the same file (really, resultant binary), so that all the tests in the binary are marked #[serial], because #[serial] from the serial_test crate only serializes #[serial] tests; it doesn't prevent non-#[serial] tests from executing concurrently with #[serial] tests. Further, all of those #[serial] tests would need to avoid spawning threads (that outlive the test). So it'd be pretty error-prone.

RalfJung · 2022-01-05T08:26:33Z

To provide a default value for RUST_LOG=debug when it wasn't already set. We'd prefer a way to do this without setting the environment variable.

Miri needs something similar here, and I think we somehow have two loggers here in this process so I don't know if we can use the env_logger API as a replacement.

cgwalters · 2022-01-05T14:17:41Z

Further, all of those #[serial] tests would need to avoid spawning threads (that outlive the test).

And even inside such a serial test, any use of e.g. tokio or rayon could spawn threads in a not immediately obvious way. So I wouldn't bet on this approach as a good mitigation.

briansmith · 2022-01-05T19:44:23Z

@cgwalters wrote:

And even inside such a serial test, any use of e.g. tokio or rayon could spawn threads in a not immediately obvious way. So I wouldn't bet on this approach as a good mitigation.

That's right. For the tests we have, what I suggested above would work. What we're more likely to do is refactor the code so that reading the environment is done separately from the functionality being tested, and then run the tests using a private API that allows us to pass in a fake environment stored in a HashMap or similar. So we have workarounds that are good enough for a lot of applications, and I don't think fully solving the testing issue should block the deprecation, as long as an unsafe variant is added during the deprecation.

briansmith · 2022-01-05T19:45:59Z

Miri needs something similar here, and I think we somehow have two loggers here in this process so I don't know if we can use the env_logger API as a replacement.

It seems like that could be solved by just making rustc_driver's log initialization API more flexible, and then taking advantage of that flexibility?

RalfJung · 2022-01-06T10:04:17Z

I am not sure how easy that would be, but yeah something like that would probably be needed.

For the other use of set_var in the cargo-miri wrapper, it would be really nice to have a way to say "all future uses of Command should set this env var"...

Per rust-lang/rust#90308, this is potentially a data race. In practice, I don't think it was actually problematic here, but it also wasn't doing anything of value, so we should remove it. This is currently the only `env::set_var` or `env::remove_var` call in the proxy. Closes linkerd/linkerd2#7651

Per rust-lang/rust#90308, this is potentially a data race. In practice, I don't think it was actually problematic here, but it also wasn't doing anything of value, so we should remove it. This is currently the only `env::set_var` or `env::remove_var` call in the proxy. To prevent uses of these functions in the future, I also added a `disallowed-methods` configuration in `.clippy.toml` to emit a warning for any uses of `std::env::set_var` and `std::env::remove_var`. Unfortunately, this required adding a `deny` attribute basically everywhere, which is why this diff touches so many files. Closes linkerd/linkerd2#7651

evanj · 2023-10-31T12:58:11Z

I ran into the Go version of this problem (see golang/go#63567 ). I think realistically, this is a small problem, and the solutions described in this thread seem reasonable. However, I am unreasonably annoyed that this problem with the C standard has been known for decades, and we can't get that fixed. I think ultimately we need the C standard to adopt a solution.

My unrealistic idea: I wish there was a way that Rust, Go and other languages that care about this (e.g. Julia? JuliaLang/julia#34726) could share a "safe" C implementation, as a way to either route around the C standard, and encourage the C standard to evolve a solution. I'm mentioning it in case others think this is interesting, because I'm annoyed enough to spend time on this.

tarcieri · 2023-10-31T13:02:21Z

@evanj there was some discussion of trying to improve the C API on IRLO: https://internals.rust-lang.org/t/thread-safe-environment-variable-mutation/17817

RalfJung · 2023-10-31T14:29:35Z

I think you are very reasonably annoyed. ;) However, where would such a shared API go? Realistically I think we'd have to convince glibc, or else we'd all have to add a new dependency to all our programs and that's just not going to fly. Maybe if people from multiple languages make a joint effort, that increases our chances of convincing glibc... Not sure.

comex · 2023-11-02T05:22:22Z

I was wondering if there was some way to implement a tiny library such that

any executable or dylib could statically link the library, but
if multiple copies of the library ended up in the same process (because multiple images each had their own statically linked copy), then the copies would somehow detect each other and agree on a single piece of shared state.

By being statically linked, the library could be included with the Rust standard library – and any other language runtimes that wanted to participate – without adding a new user-visible dependency. By sharing state, the library copies could all have a single source of truth for the current process's "thread-safe environment".

Sharing state doesn't seem that hard: on Unix, a global weak symbol would work in almost all cases. But there's at least one case where global weak symbols end up not actually being globally unique: when a dylib is linked with linker options that limit its exported symbols list. Is that a deal-breaker? Maybe not?

I also don't know how this would work on Windows, which doesn't support global weak symbols. Maybe it would suffice to not invent a new source of truth there and just use the existing thread-safe GetEnvironmentVariable/SetEnvironmentVariable.

…This is all probably a pipe dream though.

ChrisDenton · 2023-11-02T05:26:08Z

It wouldn't be needed on Windows because, as you say, modifying then environment is already thread safe.

briansmith · 2023-11-02T20:24:43Z

This issue is now over 2 years old (and we've known about it a lot longer than that). It took glibc 3 years from when getrandom was added to Linux to add support, and even now (9 years later) we still can't rely on getrandom without fallbacks. An interoperable memory-safe replacement for these APIs is realistically a decade-long (most likely, multi-decade) endeavor where most of the work would need to happen in the C/POSIX standardization and implementation space, not here. I think it would be great if somebody were to do that, but I don't think we should leave these APIs as they are for years longer.

I would also say that I don't have much hope that there would be a deprecated_safe in Rust in a timely manner. Seems like we should pursue solutions that don't involve inventing new infrastructure, such as what was suggested long ago: create new unsafe APis with new names that do the same, mark the existing APIs #[deprecated] and have them forward to the new unsafe functions, and have the deprecation note for each function reference its replacement.

jhpratt · 2023-11-02T20:30:02Z

#[deprecated_safe] would be great, but the person who was working on the implementation deleted their GitHub account; I have the branches backed up on my fork of rust-lang/rust.

There is a PR open (#94619) to add unsafe APIs with new names. I have no problem updating it to resolve the conflicts and whatever else may be necessary. It's currently marked as blocked on whether #[deprecated_safe] was going to happen, but that doesn't seem likely in the near future.

…r, r=TaKO8Ki rustc_log: provide a way to init logging based on the values, not names, of the env vars Miri wants to affect how rustc does logging. So far this required setting environment variables before calling `rustc_driver::init_rustc_env_logger`. However, `set_var` is a function one should really [avoid calling](rust-lang#90308), so this adds the necessary APIs to rustc such that Miri can just pass it the *values* of all the log-relevant environment variables, rather than having to change the global environment.

rustc_log: provide a way to init logging based on the values, not names, of the env vars Miri wants to affect how rustc does logging. So far this required setting environment variables before calling `rustc_driver::init_rustc_env_logger`. However, `set_var` is a function one should really [avoid calling](rust-lang/rust#90308), so this adds the necessary APIs to rustc such that Miri can just pass it the *values* of all the log-relevant environment variables, rather than having to change the global environment.

Allow calling these functions without `unsafe` blocks in editions up until 2021, but don't trigger the `unused_unsafe` lint for `unsafe` blocks containing these functions. Fixes rust-lang#27970. Fixes rust-lang#90308.

Make `std::env::{set_var, remove_var}` unsafe in edition 2024 Allow calling these functions without `unsafe` blocks in editions up until 2021, but don't trigger the `unused_unsafe` lint for `unsafe` blocks containing these functions. Fixes rust-lang#27970. Fixes rust-lang#90308.

Allow calling these functions without `unsafe` blocks in editions up until 2021, but don't trigger the `unused_unsafe` lint for `unsafe` blocks containing these functions. Fixes rust-lang#27970. Fixes rust-lang#90308. CC rust-lang#124866.

Make `std::env::{set_var, remove_var}` unsafe in edition 2024 Allow calling these functions without `unsafe` blocks in editions up until 2021, but don't trigger the `unused_unsafe` lint for `unsafe` blocks containing these functions. Fixes rust-lang#27970. Fixes rust-lang#90308. CC rust-lang#124866.

KamilaBorowska mentioned this issue Oct 28, 2021

The call to localtime_r may be unsound chronotope/chrono#499

Closed

crlf0710 added the T-libs-api Relevant to the library API team, which will review and decide on the PR/issue. label Nov 2, 2021

This was referenced Nov 12, 2021

Bump time to 0.3 chronotope/chrono#578

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Deprecate set_var and remove_var in 1.58.0 #90830

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jplatte mentioned this issue Dec 16, 2021

Insecure dependencies: chrono/time launchbadge/sqlx#1586

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leo60228 mentioned this issue Dec 30, 2021

Future deprecation of env::{set, remove}_var #92365

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briansmith mentioned this issue Jan 4, 2022

set_var/remove_var are unsound in combination with C code that reads the environment #27970

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briansmith mentioned this issue Jan 5, 2022

Add Backtrace::set_enabled to override environment variables #79085

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briansmith mentioned this issue Jan 5, 2022

Remove all use of std::env (for SSLKEYLOGFILE) rustls/rustls#899

Open

olix0r mentioned this issue Jan 20, 2022

test: Unsafe usage of env::set_var linkerd/linkerd2#7651

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hawkw mentioned this issue Jan 20, 2022

test: remove env::set_var call in test logging initialization linkerd/linkerd2-proxy#1437

Merged

workingjubilee added the A-process Area: `std::process` and `std::env` label Jul 22, 2023

RalfJung mentioned this issue Aug 20, 2023

Possible data race & use-after-free in std::env::var for unix implementation #114949

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jplatte mentioned this issue Oct 30, 2023

Bump tracing and update API usage matrix-org/matrix-rust-sdk#2788

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RalfJung mentioned this issue Nov 11, 2023

rustc_log: provide a way to init logging based on the values, not names, of the env vars #117814

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Enselic added the C-bug Category: This is a bug. label Dec 3, 2023

RalfJung mentioned this issue Mar 14, 2024

feature request: add support for keeping TempDir Stebalien/tempfile#194

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tbu- mentioned this issue May 2, 2024

Make std::env::{set_var, remove_var} unsafe in edition 2024 #124636

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traviscross mentioned this issue May 7, 2024

Tracking Issue for Rust 2024: Make std::env::{set_var, remove_var} unsafe #124866

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Consider deprecating and/or modifying behavior of std::env::set_var #90308

Consider deprecating and/or modifying behavior of std::env::set_var #90308

leo60228 commented Oct 26, 2021

vi commented Oct 29, 2021 •

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leo60228 commented Oct 29, 2021

tarcieri commented Oct 29, 2021 •

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RalfJung commented Jan 6, 2022

evanj commented Oct 31, 2023

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comex commented Nov 2, 2023

ChrisDenton commented Nov 2, 2023

briansmith commented Nov 2, 2023

jhpratt commented Nov 2, 2023

Consider deprecating and/or modifying behavior of std::env::set_var #90308

Consider deprecating and/or modifying behavior of std::env::set_var #90308

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leo60228 commented Oct 26, 2021

Make std::env::set_var unsafe

Don't actually call setenv

Only call setenv in single-threaded code

Deprecate std::env::set_var

vi commented Oct 29, 2021 • edited Loading

leo60228 commented Oct 29, 2021

tarcieri commented Oct 29, 2021 • edited Loading

leo60228 commented Oct 29, 2021

leo60228 commented Nov 10, 2021

cgwalters commented Nov 11, 2021

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RalfJung commented Jan 6, 2022

evanj commented Oct 31, 2023

tarcieri commented Oct 31, 2023

RalfJung commented Oct 31, 2023 via email

comex commented Nov 2, 2023

ChrisDenton commented Nov 2, 2023

briansmith commented Nov 2, 2023

jhpratt commented Nov 2, 2023

Make `std::env::set_var` unsafe

Don't actually call `setenv`

Only call `setenv` in single-threaded code

Deprecate `std::env::set_var`

vi commented Oct 29, 2021 •

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tarcieri commented Oct 29, 2021 •

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briansmith commented Jan 4, 2022 •

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Nemo157 commented Jan 4, 2022 •

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