yaahc/eyre - Change T64LKJ2RTUDFYSJQI7KF4WHZYXZHNEGNOS7ZMMCRIQZ4YN5LOOMAC

Fix potential UB by removing reliance on trait object layout Adds a raw vtable object (similar to `RawWakerVTable`) that is manually created and has methods to dynamically cast to `dyn StdError`.

Created by John Schug on October 8, 2019

T64LKJ2RTUDFYSJQI7KF4WHZYXZHNEGNOS7ZMMCRIQZ4YN5LOOMAC

Dependencies

In channels

main

Change contents

Replacement in src/error.rs at line 64 [3.3238]

B:BD[3.4743] → [4.0:76]

            let obj = mem::transmute::<&dyn StdError, TraitObject>(&error);

[3.4743]

[4.77]

            let vtable = &ErrorVTable {
                source: source_raw::<E>,
                source_mut: source_mut_raw::<E>,
            };

Replacement in src/error.rs at line 69 [3.3238]

B:BD[4.122] → [2.825:861]

                vtable: obj.vtable,

[4.122]

[5.1039]

                vtable,

Insertion in src/error.rs at line 368 [3.3238]

[3.9174]

}
struct ErrorVTable {
    source: unsafe fn(*const ()) -> *const (dyn StdError + Send + Sync + 'static),
    source_mut: unsafe fn(*mut ()) -> *mut (dyn StdError + Send + Sync + 'static),
}
unsafe fn source_raw<E>(e: *const ()) -> *const (dyn StdError + Send + Sync + 'static)
where
    E: StdError + Send + Sync + 'static,
{
    e as *const E

Insertion in src/error.rs at line 382 [3.3238]

[3.9177]

unsafe fn source_mut_raw<E>(e: *mut ()) -> *mut (dyn StdError + Send + Sync + 'static)
where
    E: StdError + Send + Sync + 'static,
{
    e as *mut E
}

Replacement in src/error.rs at line 392 [3.3238]
∅:D[6.91] → [3.9274:9297]
B:BD[3.9274] → [3.9274:9297]
```
    vtable: *const (),
```
[6.91]
[3.9297]
```
    vtable: &'static ErrorVTable,
```

Deletion in src/error.rs at line 398 [3.3238]

B:BD[3.9369] → [3.9369:9512]

// repr C to ensure that transmuting from trait objects is safe
#[repr(C)]
struct TraitObject {
    data: *const (),
    vtable: *const (),
}

Replacement in src/error.rs at line 423 [3.3238]

B:BD[7.1693] → [4.228:437]

        let object = TraitObject {
            data: &self.error,
            vtable: self.vtable,
        };
        unsafe { mem::transmute::<TraitObject, &(dyn StdError + Send + Sync + 'static)>(object) }

[7.1693]

[3.10195]

        unsafe { &*(self.vtable.source)(&self.error) }

Replacement in src/error.rs at line 427 [3.3238]

B:BD[7.1771] → [4.438:553]

∅:D[4.553] → [3.10276:10293]

∅:D[7.1771] → [3.10276:10293]

B:BD[3.10276] → [3.10276:10293]

B:BD[3.10293] → [4.554:649]

∅:D[4.649] → [3.10425:10435]

B:BD[3.10425] → [3.10425:10435]

        let object = TraitObject {
            data: &mut self.error,
            vtable: self.vtable,
        };
        unsafe {
            mem::transmute::<TraitObject, &mut (dyn StdError + Send + Sync + 'static)>(object)
        }

[7.1771]

[3.10435]

        unsafe { &mut *(self.vtable.source_mut)(&mut self.error) }