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Rollup merge of #70558 - RalfJung:vec-extend-aliasing, r=Amanieu

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Fix some aliasing issues in Vec

`Vec::extend` and `Vec::truncate` invalidated references into the vector even without reallocation, because they (implicitly) created a mutable reference covering the *entire* initialized part of the vector.

Fixes https://github.com/rust-lang/rust/issues/70301
I verified the fix by adding some new tests here that I ran in Miri.
This commit is contained in:
Dylan DPC 2020-04-05 13:13:08 +02:00 • committed by GitHub
commit 7e4ed72d64
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2 changed files with 79 additions and 14 deletions
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22
src/liballoc/vec.rs
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@ -740,7 +740,8 @@ impl<T> Vec<T> {
if len > self.len {
return;
}
let s = self.get_unchecked_mut(len..) as *mut _;
let remaining_len = self.len - len;
let s = slice::from_raw_parts_mut(self.as_mut_ptr().add(len), remaining_len);
self.len = len;
ptr::drop_in_place(s);
}
@ -963,13 +964,15 @@ impl<T> Vec<T> {
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn swap_remove(&mut self, index: usize) -> T {
let len = self.len();
assert!(index < len);
unsafe {
// We replace self[index] with the last element. Note that if the
// bounds check on hole succeeds there must be a last element (which
// bounds check above succeeds there must be a last element (which
// can be self[index] itself).
let hole: *mut T = &mut self[index];
let last = ptr::read(self.get_unchecked(self.len - 1));
self.len -= 1;
let last = ptr::read(self.as_ptr().add(len - 1));
let hole: *mut T = self.as_mut_ptr().add(index);
self.set_len(len - 1);
ptr::replace(hole, last)
}
}
@ -1200,7 +1203,7 @@ impl<T> Vec<T> {
} else {
unsafe {
self.len -= 1;
Some(ptr::read(self.get_unchecked(self.len())))
Some(ptr::read(self.as_ptr().add(self.len())))
}
}
}
@ -2020,7 +2023,7 @@ where
let (lower, _) = iterator.size_hint();
let mut vector = Vec::with_capacity(lower.saturating_add(1));
unsafe {
ptr::write(vector.get_unchecked_mut(0), element);
ptr::write(vector.as_mut_ptr(), element);
vector.set_len(1);
}
vector
@ -2122,8 +2125,9 @@ where
self.reserve(slice.len());
unsafe {
let len = self.len();
let dst_slice = slice::from_raw_parts_mut(self.as_mut_ptr().add(len), slice.len());
dst_slice.copy_from_slice(slice);
self.set_len(len + slice.len());
self.get_unchecked_mut(len..).copy_from_slice(slice);
}
}
}
@ -2144,7 +2148,7 @@ impl<T> Vec<T> {
self.reserve(lower.saturating_add(1));
}
unsafe {
ptr::write(self.get_unchecked_mut(len), element);
ptr::write(self.as_mut_ptr().add(len), element);
// NB can't overflow since we would have had to alloc the address space
self.set_len(len + 1);
}