I think writing to a const value in Rust invokes undefined behaviour. The to_mut function in bcachers.rs looked a little suspect so I made a small reproduction and ran MIRI on it. It confirmed my suspicions:
error: Undefined Behavior: trying to retag from <7013> for Unique permission at alloc2678[0x0], but that tag only grants SharedReadOnly permission for this location
This PR aims to address this. I removed the redundant initial clone of the args and shuffled the argv processing in order to avoid casting the const pointer to a mutable one.
Ideally, after the C command ran we'd call drop(Box::from_raw()) on the argv Box to free it but since it seems like the data may be in an unknown state this is not called. For example if the C code replaced one of the pointers the Rust code would try to free it, which wouldn't be right. As a result the argv data is leaked.
Since the program returns after the handle_c_command this is probably not an issue in practice. If it is an issue then further work would be needed to avoid the C code mutating the args in an incompatible way or confirm that they aren't doing anything problematic.
I think writing to a const value in Rust invokes undefined behaviour. The
to_mutfunction inbcachers.rslooked a little suspect so I made a small reproduction and ran MIRI on it. It confirmed my suspicions:You can see the reproduction here:
https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=c6d843c3a853cba49db4c20548330c36
Click Tools > Miri to run it
This PR aims to address this. I removed the redundant initial clone of the args and shuffled the argv processing in order to avoid casting the const pointer to a mutable one.
Ideally, after the C command ran we'd call
drop(Box::from_raw())on the argvBoxto free it but since it seems like the data may be in an unknown state this is not called. For example if the C code replaced one of the pointers the Rust code would try to free it, which wouldn't be right. As a result the argv data is leaked.Running MIRI on this version confirms this:
https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=245a7a2641160432a3cf56e8f172933b
Since the program returns after the
handle_c_commandthis is probably not an issue in practice. If it is an issue then further work would be needed to avoid the C code mutating the args in an incompatible way or confirm that they aren't doing anything problematic.