Opening a symlink errors using `io-uring` feature

[trxcllnt]

Description
Calling tokio::fs::File::open on a symlink returns an Operation not permitted (os error 1) error when the io-uring feature is enabled.

Platform

$ uname -a
Linux 4e7e5f758b9d 6.8.0-85-generic #85-Ubuntu SMP PREEMPT_DYNAMIC Thu Sep 18 15:26:59 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux

Version

$ cargo tree | grep tokio
│   └── tokio v1.48.0
│       └── tokio-macros v2.6.0 (proc-macro)
│   │   ├── tokio v1.48.0 (*)
│   │   ├── tokio-util v0.7.16
│   │   │   └── tokio v1.48.0 (*)
│   ├── tokio v1.48.0 (*)
│   ├── tokio v1.48.0 (*)
│   │   └── tokio v1.48.0 (*)
│   │   │   ├── tokio v1.48.0 (*)
│   │   │   └── tokio-util v0.7.16 (*)
│   │   ├── tokio v1.48.0 (*)
│   │   ├── tokio-rustls v0.26.0
│   │   │   └── tokio v1.48.0 (*)
│   │   ├── tokio-util v0.7.16 (*)
│   │   │   │   ├── tokio v1.48.0 (*)
│   │   │   │   ├── tokio-rustls v0.26.0 (*)
│   │   │   │   ├── tokio v1.48.0 (*)
│   │   │   │   ├── tokio-native-tls v0.3.1
│   │   │   │   │   └── tokio v1.48.0 (*)
│   │   │   ├── tokio v1.48.0 (*)
│   │   │   ├── tokio-native-tls v0.3.1 (*)
│   │   │   ├── tokio-rustls v0.26.0 (*)
│   │   │   ├── tokio-util v0.7.16 (*)
│   │   │   │   ├── tokio v1.48.0 (*)
│   │   └── tokio v1.48.0 (*)
│   ├── tokio v1.48.0 (*)
│   ├── reqsign-command-execute-tokio v2.0.0
│   │   └── tokio v1.48.0 (*)
│   ├── reqsign-file-read-tokio v2.0.0
│   │   └── tokio v1.48.0 (*)
├── tokio v1.48.0 (*)
├── tokio-retry2 v0.5.6
│   └── tokio v1.48.0 (*)
├── tokio-serde v0.8.0
├── tokio-util v0.7.16 (*)
│   │   │   ├── tokio v1.48.0 (*)
│   │   │   ├── tokio-util v0.7.16 (*)
│   │   │   ├── tokio v1.48.0 (*)
│   │   │   ├── tokio v1.48.0 (*)
│   │   │   └── tokio-native-tls v0.3.1 (*)
│   │   ├── tokio v1.48.0 (*)
│   │   ├── tokio-native-tls v0.3.1 (*)
│       ├── tokio v1.48.0 (*)

[ADD-SP]

$ uname -a
Linux xxx 6.8.0-85-generic #85-Ubuntu SMP PREEMPT_DYNAMIC Thu Sep 18 15:26:59 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux

$ ln -s Cargo.toml a.toml

$ tree -L 1 --gitignore 
.
├── a.toml -> Cargo.toml
├── Cargo.lock
├── Cargo.toml
└── src

$ RUSTFLAGS='--cfg tokio_unstable' cargo run

use tokio::io::AsyncReadExt;

async fn main() {
    let mut file = tokio::fs::OpenOptions::new().read(true).open("a.toml").await.unwrap();
    let mut buffer = vec![0; 1024];
    file.read_to_end(&mut buffer).await.unwrap();
    dbg!(&buffer);
}

[dependencies]
tokio = { version = "1.48.0", features = ["full", "io-uring"] }

I can't reproduce this issue locally, do you have a minimal reproducible example?

[trxcllnt]

Sure can. I saw the error in a container, so here's a repro using rust:latest:

$ docker --version
Docker version 28.5.0, build 887030f

$ docker run --rm rust:latest bash -c "$(cat <<"EOF"
mkdir -p /tmp/test/src
cd /tmp/test
ln -s Cargo.toml a.toml

cat <<"EOF2" > Cargo.toml
[package]
edition = "2024"
name = "tokio-io-uring-symlink"

[dependencies]
tokio = { version = "1.48.0", features = ["full", "io-uring"] }
EOF2

cat <<"EOF2" > src/main.rs
#[tokio::main]
async fn main() {
    tokio::fs::File::open("a.toml").await.unwrap();
}
EOF2

RUSTFLAGS='--cfg tokio_unstable' cargo run
EOF
)"
> ...
> thread 'main' panicked at src/main.rs:3:43:
> called `Result::unwrap()` on an `Err` value: Os { code: 1, kind: PermissionDenied, message: "Operation not permitted" }
> note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

[ADD-SP]

Ah, it's the container. You could try docker run --privileged to see if this still happens.

[Darksonn]

Also, please run the same code without using io-uring to confirm that this only happens with io-uring.

[trxcllnt]

Yep, confirmed removing the io-uring feature from the above example runs fine.

[trxcllnt]

@ADD-SP You're right, --privileged also runs without error. That's a fairly major new requirement though, and some container engines (AWS Fargate etc.) disallow privileged mode entirely, so I worry that makes it out of reach for many users.

[ADD-SP]

Currently, this unstable feature is not enabled by default, it should be ok. But yes, enabling this by default is a breaking change due to extra permission is required. I have posted your concern in #7266 (comment).