Merge pull request #1317 from yotamofek/swap-unchecked-ub
Fix UB in `RawStorageMut::swap_unchecked_linear`
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749a9fee17
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@ -206,10 +206,28 @@ pub unsafe trait RawStorageMut<T, R: Dim, C: Dim = U1>: RawStorage<T, R, C> {
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///
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///
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/// # Safety
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/// # Safety
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/// If the indices are out of bounds, the method will cause undefined behavior.
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/// If the indices are out of bounds, the method will cause undefined behavior.
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///
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/// # Validity
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/// The default implementation of this trait function is only guaranteed to be
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/// sound if invocations of `self.ptr_mut()` and `self.get_address_unchecked_linear_mut()`
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/// result in stable references. If any of the data pointed to by these trait methods
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/// moves as a consequence of invoking either of these methods then this default
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/// trait implementation may be invalid or unsound and should be overridden.
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#[inline]
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#[inline]
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unsafe fn swap_unchecked_linear(&mut self, i1: usize, i2: usize) {
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unsafe fn swap_unchecked_linear(&mut self, i1: usize, i2: usize) {
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let a = self.get_address_unchecked_linear_mut(i1);
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// we can't just use the pointers returned from `get_address_unchecked_linear_mut` because calling a
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let b = self.get_address_unchecked_linear_mut(i2);
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// method taking self mutably invalidates any existing (mutable) pointers. since `get_address_unchecked_linear_mut` can
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// also be overriden by a custom implementation, we can't just use `wrapping_add` assuming that's what the method does.
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// instead, we use `offset_from` to compute the re-calculate the pointers from the base pointer.
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// this is sound as long as this trait matches the Validity preconditions
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// (and it's the caller's responsibility to ensure the indices are in-bounds).
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let base = self.ptr_mut();
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let offset1 = self.get_address_unchecked_linear_mut(i1).offset_from(base);
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let offset2 = self.get_address_unchecked_linear_mut(i2).offset_from(base);
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let base = self.ptr_mut();
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let a = base.offset(offset1);
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let b = base.offset(offset2);
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ptr::swap(a, b);
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ptr::swap(a, b);
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}
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}
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