RUSTSEC-2020-0059

MutexGuard::map can cause a data race in safe code

Issued
Package
futures-util (crates.io)
Type
Vulnerability
Categories
  • thread-safety
Aliases
Details
https://github.com/rust-lang/futures-rs/issues/2239
Patched
  • >=0.3.7
Unaffected
  • <0.3.2
Keywords
  • concurrency
  • memory-corruption
  • memory-management
Affected Functions
Version
futures_util::lock::MutexGuard::map
  • >=0.3.2

Description

Affected versions of the crate had a Send/Sync implementation for MappedMutexGuard that only considered variance on T, while MappedMutexGuard dereferenced to U.

This could of led to data races in safe Rust code when a closure used in MutexGuard::map() returns U that is unrelated to T.

The issue was fixed by fixing Send and Sync implementations, and by adding a PhantomData<&'a mut U> marker to the MappedMutexGuard type to tell the compiler that the guard is over U too.

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