Fix UB dropping BoxBytes with a zero-sized layout #258
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Merged
kupiakos
reviewed
Aug 9, 2024
| // `layout.size()` initialized bytes. | ||
| // SAFETY: `ptr` is owned, points to `layout.size()` initialized bytes, and | ||
| // was allocated with `layout` (unless `layout.size() == 0` in which case it | ||
| // is dangling). |
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Note: this terminology is incorrect according to Rust's definition. A pointer to zero-sized data is never dangling, since all zero-sized reads and writes are now considered valid, even with a null pointer.
The primary issue is that dealloc requires that the layout not be zero-sized; whether the pointer dangles is irrelevant.
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That is definitely true in a strict sense, and a follow up PR for fixing that note would be appropriate if you wanted to do that, because safety notes should not be loose with wording.
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Boxdoes not actually perform an allocation for zero-sized values, soBoxBytes::dropshould not calldeallocifself.layout.size() == 0.