Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Wed, 12 Jun 2019 10:24:04 +0100
From:   Mark Rutland <mark.rutland@arm.com>
To:     Stephen Bates <sbates@raithlin.com>
Cc:     "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
        "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Jens Axboe <axboe@kernel.dk>,
        "shhuiw@foxmail.com" <shhuiw@foxmail.com>,
        Logan Gunthorpe <logang@deltatee.com>,
        "viro@zeniv.linux.org.uk" <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH] io_uring: fix SQPOLL cpu check
Message-ID: <20190612092403.GA38578@lakrids.cambridge.arm.com>
References: <5D2859FE-DB39-48F5-BBB5-6EDD3791B6C3@raithlin.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <5D2859FE-DB39-48F5-BBB5-6EDD3791B6C3@raithlin.com>
User-Agent: Mutt/1.11.1+11 (2f07cb52) (2018-12-01)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, Jun 11, 2019 at 11:56:06PM +0000, Stephen  Bates wrote:
> The array_index_nospec() check in io_sq_offload_start() is performed
> before any checks on p->sq_thread_cpu are done. This means cpu is
> clamped and therefore no error occurs when out-of-range values are
> passed in from userspace. This is in violation of the specification
> for io_ring_setup() and causes the io_ring_setup unit test in liburing
> to regress.
> 
> Add a new bounds check on sq_thread_cpu at the start of
> io_sq_offload_start() so we can exit the function early when bad
> values are passed in.
> 
> Fixes: 975554b03edd ("io_uring: fix SQPOLL cpu validation")
> Signed-off-by: Stephen Bates <sbates@raithlin.com>

Aargh. My original patch [1] handled that correctly, and this case was
explicitly called out in the commit message, which was retained even
when the patch was "simplified". That's rather disappointing. :/

Thanks,
Mark.

[1] https://lore.kernel.org/lkml/20190430123451.44227-1-mark.rutland@arm.com/

> ---
>  fs/io_uring.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 30a5687..e458470 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -2316,6 +2316,9 @@ static int io_sq_offload_start(struct io_ring_ctx *ctx,
>  {
>  	int ret;
>  
> +	if (p->sq_thread_cpu >= nr_cpu_ids)
> +		return -EINVAL;
> +
>  	init_waitqueue_head(&ctx->sqo_wait);
>  	mmgrab(current->mm);
>  	ctx->sqo_mm = current->mm;
> -- 
> 2.7.4
>