bug: undefined behavior when transmuting u32 to various enums

[antonilol]

in several places in the code a u32 is transmuted to enums without any checks. examples include

rust-sdl2/src/sdl2/render.rs

Line 118 in 146cff6

Ok(match unsafe { transmute(n) } {

,

rust-sdl2/src/sdl2/render.rs

Line 172 in 146cff6

Ok(match unsafe { transmute(n) } {

and

rust-sdl2/src/sdl2/pixels.rs

Line 448 in 146cff6

Ok(match unsafe { transmute(n) } {

.

these TryInto implementations are public so this can be easily demonstrated by using miri with the code let b: BlendMode = 3.try_into() (this calls <BlendMode as TryFrom<u32>>::try_from(3) with the invalid value 3) for example:

error: Undefined Behavior: constructing invalid value at .<enum-tag>: encountered 0x00000003, but expected a valid enum tag
   --> /home/antoni/.cargo/registry/src/index.crates.io-6f17d22bba15001f/sdl2-0.36.0/src/sdl2/render.rs:172:27
    |
172 |         Ok(match unsafe { transmute(n) } {
    |                           ^^^^^^^^^^^^ constructing invalid value at .<enum-tag>: encountered 0x00000003, but expected a valid enum tag
    |
    = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior
    = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information
    = note: BACKTRACE:
    = note: inside `<sdl2::render::BlendMode as std::convert::TryFrom<u32>>::try_from` at /home/antoni/.cargo/registry/src/index.crates.io-6f17d22bba15001f/sdl2-0.36.0/src/sdl2/render.rs:172:27: 172:39
    = note: inside `<u32 as std::convert::TryInto<sdl2::render::BlendMode>>::try_into` at /home/antoni/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/convert/mod.rs:798:9: 798:26

[jagprog5]

@antonilol this is fixed in my merge request: #1444

cc @Cobrand

[antonilol]

@antonilol this is fixed in my merge request: #1444

Not completely, a quick search found (every line containing transmute and match):

• src/sdl2/event.rs:420 (probably alright)
• src/sdl2/audio.rs:340 (unsound)
• src/sdl2/keyboard/scancode.rs:261 (unsound)
• src/sdl2/keyboard/keycode.rs:486 (unsound)

There could be more, so please make sure you got them all before closing this issue.

[jagprog5]

@antonilol Thanks, I've updated my comment in the MR to reflect this.

I've decided not to amend the MR further:

• scope creep
• I think this repo is no longer active, which would be a shame. @Cobrand @AngryLawyer looking for maintainers?

[antonilol]

• I think this repo is no longer active, which would be a shame.

Yes, even if people switch to SDL3 (I don't know how stable the Rust bindings for SDL3 are already), people still use SDL2 so at least undefined behavior should be fixed here.
Also, the SDL3 bindings repo was forked from this repo, so fixes could potentially be reused there.

[Cobrand]

I think this repo is no longer active, which would be a shame.

It depends what you call maintained. I still look at PRs and merge them from time to time, although probably not as often as some of you would expect. If it was as easy as click "merge", I would do it more often, but unfortunately you have to read them, ask for changes, wait for them to answer, and if they don't take their changes to adapt them and merge them, sometimes fix merge conflicts, and that for every single PR.

Yes I do need maintainers or help in general, I have been calling it for years. Originally I just offered to take a bit of the burden, next thing I know I'm the only maintainer left and no one is stepping up. It has been this way for 8 years, almost 9 now. I think you can understand that it's not always easy to look at everything that's being thrown at you every week for that long while still keeping decent delays.

Sorry to be a bit pissy but it's a bit like the "no take, only throw" image, people expect it to be maintained, but no one is stepping up to help either.

Yes I will look at the issues/PRs at some point, no I don't have an estimate of when I will, yes help would be really appreciated. Thanks.

[jagprog5]

Yessir, I totally get it. Open source is thankless and this is a big repo, especially for one person. How can I help out? Can I be a maintainer?

[Cobrand]

Currently I'm trying to contact AngryLawyer (the original repo owner), so that I can add other members to the organization myself, once I can do that I'll definitely add new maintainers yes.

[jagprog5]

@antonilol Things have changed! I'm now a maintainer. Feel free to open a PR for this

[antonilol]

@antonilol Things have changed! I'm now a maintainer. Feel free to open a PR for this

I will wait on #1444 to not do double work, looking for how exactly the match statements end up.
In the meantime, I have 7 other pull requests open that can be reviewed. Ignore the merge conflicts until just before merging, 6 of those 7 add an entry to the changelog which git does not know whether it should go above or below changelog entries of other recently merged PRs.