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String::push_str invalidates interior references even when it does not reallocate #70301
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Yeah this looks pretty similar. Looks like fn main() {
let mut v = Vec::with_capacity(10);
v.push(0);
let v0 = unsafe { &*(&v[0] as *const _) }; // laundering the lifetime -- we take care that `v` does not reallocate, so that's okay.
v.extend_from_slice(&[1]);
let _val = *v0;
} |
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The problem is in this line: Line 2125 in 8ff7850 The |
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It shouldn't be too hard to locally fix this, but that duplicates some code and there are some other uses of |
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Here's a possible fix: diff --git a/src/liballoc/vec.rs b/src/liballoc/vec.rs
index 4769091183a..fd2b336eceb 100644
--- a/src/liballoc/vec.rs
+++ b/src/liballoc/vec.rs
@@ -2121,8 +2121,9 @@ 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);
}
}
} |
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Fix PR is up: #70558 |
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 rust-lang#70301 I verified the fix by adding some new tests to Miri: rust-lang/miri#1253
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 rust-lang#70301 I verified the fix by adding some new tests to Miri: rust-lang/miri#1253
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 rust-lang#70301 I verified the fix by adding some new tests here that I ran in Miri.
test Vec::extend Currently fails, until rust-lang/rust#70301 gets fixed.
To my knowledge, the following code is intended to be legal:
However, Miri currently flags this as UB.
I believe this is #60847, but for
String. Discovered while writing this post.cc @RalfJung