Merge pull request #1317 from yotamofek/swap-unchecked-ub

Fix UB in `RawStorageMut::swap_unchecked_linear`
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tpdickso 2024-03-27 20:44:39 -04:00 committed by GitHub
commit 749a9fee17
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1 changed files with 20 additions and 2 deletions

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@ -206,10 +206,28 @@ pub unsafe trait RawStorageMut<T, R: Dim, C: Dim = U1>: RawStorage<T, R, C> {
///
/// # Safety
/// If the indices are out of bounds, the method will cause undefined behavior.
///
/// # Validity
/// The default implementation of this trait function is only guaranteed to be
/// sound if invocations of `self.ptr_mut()` and `self.get_address_unchecked_linear_mut()`
/// result in stable references. If any of the data pointed to by these trait methods
/// moves as a consequence of invoking either of these methods then this default
/// trait implementation may be invalid or unsound and should be overridden.
#[inline]
unsafe fn swap_unchecked_linear(&mut self, i1: usize, i2: usize) {
let a = self.get_address_unchecked_linear_mut(i1);
let b = self.get_address_unchecked_linear_mut(i2);
// we can't just use the pointers returned from `get_address_unchecked_linear_mut` because calling a
// method taking self mutably invalidates any existing (mutable) pointers. since `get_address_unchecked_linear_mut` can
// also be overriden by a custom implementation, we can't just use `wrapping_add` assuming that's what the method does.
// instead, we use `offset_from` to compute the re-calculate the pointers from the base pointer.
// this is sound as long as this trait matches the Validity preconditions
// (and it's the caller's responsibility to ensure the indices are in-bounds).
let base = self.ptr_mut();
let offset1 = self.get_address_unchecked_linear_mut(i1).offset_from(base);
let offset2 = self.get_address_unchecked_linear_mut(i2).offset_from(base);
let base = self.ptr_mut();
let a = base.offset(offset1);
let b = base.offset(offset2);
ptr::swap(a, b);
}