PT-2026-55815 · Crates.Io · Anyhow
Published
2026-06-25
·
Updated
2026-06-25
None
No severity ratings or metrics are available. When they are, we'll update the corresponding info on the page.
Affected versions of this crate violate borrow rules, resulting in undefined behavior, when the user adds context to an error via
Error::context and then later calls Error::downcast mut on the returned Error.The flaw was corrected in commit
6e8c000 by revising how the mutable reference is constructed, avoiding inclusion of a shared reference in the resulting borrow chain.Example
rust
use anyhow::Error;
use std::fmt;
#[derive(Debug)]
struct ErrorContext(&'static str);
impl fmt::Display for ErrorContext {
fn fmt(&self, f: &mut fmt::Formatter<' >) -> fmt::Result {
fmt::Display::fmt(&self.0, f)
}
}
fn main() {
let mut error = Error::msg("inner error").context(ErrorContext("old context"));
let context: &mut ErrorContext = error.downcast mut().unwrap();
context.0 = "new context";
println!("{:?}", error);
}Miri output
error: Undefined Behavior: trying to retag from <1538> for Unique permission at alloc602[0x38], but that tag only grants SharedReadOnly permission for this location
--> src/ptr.rs:170:18
|
170 | unsafe { &mut *self.ptr.as ptr() }
| ^^^^^^^^^^^^^^^^^^^^^^^ this error occurs as part of retag at alloc602[0x38..0x48]
|
= help: this indicates a potential bug in the program: it performed an invalid operation, but the Stacked Borrows rules it violated are still experimental
= help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/stacked-borrows.md for further information
help: <1538> was created by a SharedReadOnly retag at offsets [0x38..0x48]
--> src/ptr.rs:89:18
|
89 | ptr: NonNull::from(ptr),
| ^^^^^^^^^^^^^^^^^^
= note: stack backtrace:
0: anyhow::ptr::Mut::<' , ErrorContext>::deref mut
at src/ptr.rs:170:18: 170:41
1: anyhow::error::<impl anyhow::Error>::downcast mut::<ErrorContext>
at src/error.rs:560:18: 560:46
2: main
at examples/downcast mut.rs:15:38: 15:58 Found an issue in the description? Have something to add? Feel free to write us 👾
Related Identifiers
Affected Products
Anyhow