Re: [PATCH] fs/io_uring: fix O_PATH fds in openat, openat2, statx

From: Al Viro <viro@zeniv.linux.org.uk>
To: Jens Axboe <axboe@kernel.dk>
Cc: Max Kellermann <mk@cm4all.com>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	stable@vger.kernel.org
Subject: Re: [PATCH] fs/io_uring: fix O_PATH fds in openat, openat2, statx
Date: Thu, 7 May 2020 23:06:37 +0100	[thread overview]
Message-ID: <20200507220637.GH23230@ZenIV.linux.org.uk> (raw)
In-Reply-To: <8e3c88cc-027b-4f90-b4f8-a20d11d35c4b@kernel.dk>

On Thu, May 07, 2020 at 02:53:30PM -0600, Jens Axboe wrote:

> I think the patch is correct as-is, I took a good look at how we're
> currently handling it. None of those three ops should fiddle with
> the fd at all, and all of them do forbid the use of fixed files (the
> descriptor table look-alikes), so that part is fine, too.
> 
> There's some low hanging fruit around optimizing and improving it,
> I'm including an updated version below. Max, can you double check
> with your testing?

<looks>

Could you explain WTF is io_issue_sqe() doing in case of IORING_OP_CLOSE?
Specifically, what is the value of
        req->close.fd = READ_ONCE(sqe->fd);
        if (req->file->f_op == &io_uring_fops ||
            req->close.fd == req->ctx->ring_fd)
                return -EBADF;
in io_close_prep()?  And what does happen if some joker does dup2()
of something with io_uring_fops into our slot right after that check?
Before the subsequent
        ret = __close_fd_get_file(req->close.fd, &req->close.put_file);
that is.