linux-kernel - Re: [RFC PATCH v3 2/5] io_uring/cmd: zero-init pdu in io_uring_cmd

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Message-ID: <CADUfDZpsePAbEON_90frzrPCPBt-a=1sW2Q=i8BGS=+tZhudFA@mail.gmail.com>
Date: Mon, 1 Sep 2025 17:34:28 -0700
From: Caleb Sander Mateos <csander@...estorage.com>
To: Sidong Yang <sidong.yang@...iosa.ai>
Cc: Jens Axboe <axboe@...nel.dk>, Daniel Almeida <daniel.almeida@...labora.com>, 
	Benno Lossin <lossin@...nel.org>, Miguel Ojeda <ojeda@...nel.org>, Arnd Bergmann <arnd@...db.de>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org, io-uring@...r.kernel.org
Subject: Re: [RFC PATCH v3 2/5] io_uring/cmd: zero-init pdu in
 io_uring_cmd_prep() to avoid UB

On Fri, Aug 22, 2025 at 5:56 AM Sidong Yang <sidong.yang@...iosa.ai> wrote:
>
> The pdu field in io_uring_cmd may contain stale data when a request
> object is recycled from the slab cache. Accessing uninitialized or
> garbage memory can lead to undefined behavior in users of the pdu.
>
> Ensure the pdu buffer is cleared during io_uring_cmd_prep() so that
> each command starts from a well-defined state. This avoids exposing
> uninitialized memory and prevents potential misinterpretation of data
> from previous requests.
>
> No functional change is intended other than guaranteeing that pdu is
> always zero-initialized before use.
>
> Signed-off-by: Sidong Yang <sidong.yang@...iosa.ai>
> ---
>  io_uring/uring_cmd.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
> index 053bac89b6c0..2492525d4e43 100644
> --- a/io_uring/uring_cmd.c
> +++ b/io_uring/uring_cmd.c
> @@ -203,6 +203,7 @@ int io_uring_cmd_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
>         if (!ac)
>                 return -ENOMEM;
>         ioucmd->sqe = sqe;
> +       memset(&ioucmd->pdu, 0, sizeof(ioucmd->pdu));

Adding this overhead to every existing uring_cmd() implementation is
unfortunate. Could we instead track the initialized/uninitialized
state by using different types on the Rust side? The io_uring_cmd
could start as an IoUringCmd, where the PDU field is MaybeUninit,
write_pdu<T>() could return a new IoUringCmdPdu<T> that guarantees the
PDU has been initialized.

Best,
Caleb

>         return 0;
>  }
>
> --
> 2.43.0
>