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Subject: Re: [PATCH] io_uring: fix compat for IORING_REGISTER_FILES_UPDATE
To:     Eugene Syromiatnikov <esyr@redhat.com>,
        linux-fsdevel@vger.kernel.org, io-uring@vger.kernel.org,
        Alexander Viro <viro@zeniv.linux.org.uk>
Cc:     linux-kernel@vger.kernel.org, Jeff Moyer <jmoyer@redhat.com>,
        "Dmitry V. Levin" <ldv@altlinux.org>
References: <20200115163538.GA13732@asgard.redhat.com>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <cce5ac48-641d-3051-d22c-dab7aaa5704c@kernel.dk>
Date:   Wed, 15 Jan 2020 09:41:58 -0700
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On 1/15/20 9:35 AM, Eugene Syromiatnikov wrote:
> fds field of struct io_uring_files_update is problematic with regards
> to compat user space, as pointer size is different in 32-bit, 32-on-64-bit,
> and 64-bit user space.  In order to avoid custom handling of compat in
> the syscall implementation, make fds __u64 and use u64_to_user_ptr in
> order to retrieve it.  Also, align the field naturally and check that
> no garbage is passed there.

Good point, it's an s32 pointer so won't align nicely. But how about
just having it be:

struct io_uring_files_update {
	__u32 offset;
	__u32 resv;
	__s32 *fds;
};

which should align nicely on both 32 and 64-bit?

-- 
Jens Axboe