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Message-ID: <20200908134448.sg7evdrfn6xa67sn@steredhat>
Date: Tue, 8 Sep 2020 15:44:48 +0200
From: Stefano Garzarella <sgarzare@...hat.com>
To: Jens Axboe <axboe@...nel.dk>
Cc: Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Christian Brauner <christian.brauner@...ntu.com>,
linux-fsdevel@...r.kernel.org, io-uring@...r.kernel.org,
Alexander Viro <viro@...iv.linux.org.uk>,
Stefan Hajnoczi <stefanha@...hat.com>, Jann Horn <jannh@...gle.com>,
Jeff Moyer <jmoyer@...hat.com>, Aleksa Sarai <asarai@...e.de>,
Sargun Dhillon <sargun@...gun.me>, linux-kernel@...r.kernel.org,
Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH v6 3/3] io_uring: allow disabling rings during the
creation
Hi Jens,
On Thu, Aug 27, 2020 at 04:58:31PM +0200, Stefano Garzarella wrote:
> This patch adds a new IORING_SETUP_R_DISABLED flag to start the
> rings disabled, allowing the user to register restrictions,
> buffers, files, before to start processing SQEs.
>
> When IORING_SETUP_R_DISABLED is set, SQE are not processed and
> SQPOLL kthread is not started.
>
> The restrictions registration are allowed only when the rings
> are disable to prevent concurrency issue while processing SQEs.
>
> The rings can be enabled using IORING_REGISTER_ENABLE_RINGS
> opcode with io_uring_register(2).
>
> Suggested-by: Jens Axboe <axboe@...nel.dk>
> Reviewed-by: Kees Cook <keescook@...omium.org>
> Signed-off-by: Stefano Garzarella <sgarzare@...hat.com>
> ---
> v4:
> - fixed io_uring_enter() exit path when ring is disabled
>
> v3:
> - enabled restrictions only when the rings start
>
> RFC v2:
> - removed return value of io_sq_offload_start()
> ---
> fs/io_uring.c | 52 ++++++++++++++++++++++++++++++-----
> include/uapi/linux/io_uring.h | 2 ++
> 2 files changed, 47 insertions(+), 7 deletions(-)
>
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 5f62997c147b..b036f3373fbe 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -226,6 +226,7 @@ struct io_restriction {
> DECLARE_BITMAP(sqe_op, IORING_OP_LAST);
> u8 sqe_flags_allowed;
> u8 sqe_flags_required;
> + bool registered;
> };
>
> struct io_ring_ctx {
> @@ -7497,8 +7498,8 @@ static int io_init_wq_offload(struct io_ring_ctx *ctx,
> return ret;
> }
>
> -static int io_sq_offload_start(struct io_ring_ctx *ctx,
> - struct io_uring_params *p)
> +static int io_sq_offload_create(struct io_ring_ctx *ctx,
> + struct io_uring_params *p)
> {
> int ret;
>
> @@ -7532,7 +7533,6 @@ static int io_sq_offload_start(struct io_ring_ctx *ctx,
> ctx->sqo_thread = NULL;
> goto err;
> }
> - wake_up_process(ctx->sqo_thread);
> } else if (p->flags & IORING_SETUP_SQ_AFF) {
> /* Can't have SQ_AFF without SQPOLL */
> ret = -EINVAL;
> @@ -7549,6 +7549,12 @@ static int io_sq_offload_start(struct io_ring_ctx *ctx,
> return ret;
> }
>
> +static void io_sq_offload_start(struct io_ring_ctx *ctx)
> +{
> + if ((ctx->flags & IORING_SETUP_SQPOLL) && ctx->sqo_thread)
> + wake_up_process(ctx->sqo_thread);
> +}
> +
> static inline void __io_unaccount_mem(struct user_struct *user,
> unsigned long nr_pages)
> {
> @@ -8295,6 +8301,9 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
> if (!percpu_ref_tryget(&ctx->refs))
> goto out_fput;
>
> + if (ctx->flags & IORING_SETUP_R_DISABLED)
> + goto out_fput;
> +
While writing the man page paragraph, I discovered that if the rings are
disabled I returned ENXIO error in io_uring_enter(), coming from the previous
check.
I'm not sure it is the best one, maybe I can return EBADFD or another
error.
What do you suggest?
I'll add a test for this case.
Thanks,
Stefano
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