Crate smartalloc

This crate provides a no_std idiomatic Rust binding to smartalloc used for detecting orphaned buffer allocation which is a type of heap memory leak that the program has lost all access to it. The primary usecase is as a debugging tool when writing unsafe code where normal Rust static checks are not available. It is best used along side SANs where SANs alone are either unable to detect or their outputs are cumbersome to work through. To get the best experience, RUSTFLAGS=-Zsanitizer=leak is used and is included in .cargo/config.toml.

Usage

[dev-dependencies]
smartalloc = "0.2"

In fact, with #![cfg(debug_assertions)] the crate does not compile in the --release mode so preventing from any accidental usage. The crate requires nightly Rust toolchain (MSRV 1.65).

Example

During debugging, configure the SmartAlloc as the global allocator. Then include sm_dump(true) at the end of an unsafe code block. Here is the examples/orphan.rs

use core::alloc::{GlobalAlloc, Layout};

use smartalloc::{sm_dump, SmartAlloc};

#[global_allocator]
static GLOBAL: SmartAlloc = SmartAlloc;

fn main() {
    unsafe {
        let alloc = SmartAlloc;
        let layout = Layout::from_size_align(8, 8).unwrap();
        alloc.alloc(layout); // orphaned memory leak as it's pointer is lost
                             // and there's no alloc.dealloc(ptr, layout)
        sm_dump(true);
    }
}

which outputs

Orphaned buffer:       8 bytes allocated at line 12 of examples/orphan.rs

Note that the detector also throws

Orphaned buffer:       5 bytes allocated at line 5 of examples/orphan.rs
Orphaned buffer:      48 bytes allocated at line 5 of examples/orphan.rs

which refers to the #[global_allocator] itself and can be ignored.

Features

The detector can be turned off using sm_static(true) and turned back on sm_static(false) to wrap cases where allocation is done through std or safe cases such as examples/native.rs. For more details, checkout the original docs.

Aren’t SANs alone supposed to detect such errors?

Neither of the leak/address/memory sanitizers are sufficient and can detect such errors easily. In fact, running

RUSTFLAGS="-Zsanitizer=leak" cargo +nightly run --example undetected
// OR
RUSTFLAGS="-Zsanitizer=address" cargo +nightly run --example undetected

for examples/undetected.rs which is

unsafe {
    let alloc = SmartAlloc;
    let layout = Layout::from_size_align(8, 8).unwrap();
    alloc.alloc(layout);
}

with no sm_dump(true) at the end, does not show anything, mainly because we specified

[profile.dev]
opt-level = 0

for the SmartAlloc to work with introspection as opposed to what has been advised to include (at least opt-level=1) here to cirvumvent such a limitation but when is done the context gets destroyed. Also

RUSTFLAGS="-Zsanitizer=memory -Zsanitizer-memory-track-origins" cargo +nightly run --example undetected

cannot compile and it throws unhelpful messages

error: failed to run custom build command for `libc v0.2.132`

Caused by:
  process didn't exit successfully: `/home/workspace/smartalloc-rs/target/debug/build/libc-02d4e594eff5723f/build-script-build` (exit status: 1)
  --- stdout
  cargo:rerun-if-changed=build.rs

  --- stderr
  ==186416==WARNING: MemorySanitizer: use-of-uninitialized-value
    #0 0x56367729226c  (/home/workspace/smartalloc-rs/target/debug/build/libc-02d4e594eff5723f/build-script-build+0x7a26c) (BuildId: ff090caba1904387acf3f0fecb58801c6fa5caed)
    #1 0x56367728e95d  (/home/workspace/smartalloc-rs/target/debug/build/libc-02d4e594eff5723f/build-script-build+0x7695d) (BuildId: ff090caba1904387acf3f0fecb58801c6fa5caed)
    ...
    Uninitialized value was created by an allocation of '_2' in the stack frame of function '_ZN18build_script_build19rustc_minor_nightly17hfbf53e202478a57bE'
      #0 0x563677291e70  (/home/workspace/smartalloc-rs/target/debug/build/libc-02d4e594eff5723f/build-script-build+0x79e70) (BuildId: ff090caba1904387acf3f0fecb58801c6fa5caed)

    SUMMARY: MemorySanitizer: use-of-uninitialized-value (/home/workspace/smartalloc-rs/target/debug/build/libc-02d4e594eff5723f/build-script-build+0x7a26c) (BuildId: ff090caba1904387acf3f0fecb58801c6fa5caed)
    Exiting

so it needs more work!

Known issue

smartalloc-sys/csrc/smartall.c writes into the passed filename pointer tracked by #[track_caller] (which is immutable) which is an UB that could result into displaying more garbage after the filename in its report using this binding.

Structs

SmartAlloc

SmartAlloc allocator which needs to be use with #[global_allocator]

Functions

sm_dump

Prints orphaned buffers when enabled true with the number of allocated bytes and the line location in source code

sm_static

Orphaned buffer detection can be disabled (for such items as buffers allocated during initialisation) by calling sm_static(true). Normal orphaned buffer detection can be re-enabled with sm_static(false). Note that all the other safeguards still apply to buffers allocated when sm_static(true) mode is in effect.