linux-kernel - Re: [PATCH v6 02/16] chardev: introduce cdev_get_by

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Date:   Thu, 25 Jul 2019 12:45:15 -0700
From:   Sagi Grimberg <sagi@...mberg.me>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Logan Gunthorpe <logang@...tatee.com>,
        linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
        linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Christoph Hellwig <hch@....de>,
        Keith Busch <kbusch@...nel.org>, Jens Axboe <axboe@...com>,
        Chaitanya Kulkarni <Chaitanya.Kulkarni@....com>,
        Max Gurtovoy <maxg@...lanox.com>,
        Stephen Bates <sbates@...thlin.com>,
        Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH v6 02/16] chardev: introduce cdev_get_by_path()


>>> So, as was kind of alluded to in another part of the thread, what are
>>> you doing about permissions?  It seems that any user/group permissions
>>> are out the window when you have the kernel itself do the opening of the
>>> char device, right?  Why is that ok?  You can pass it _any_ character
>>> device node and away it goes?  What if you give it a "wrong" one?  Char
>>> devices are very different from block devices this way.
>>
>> We could condition any configfs operation on capable(CAP_NET_ADMIN) to
>> close that hole for now..
> 
> Why that specific permission?

Meant CAP_SYS_ADMIN

> And what about the "pass any random char device name" issue?  What
> happens if you pass /dev/random/ as the string?

What is the difference if the application is opening the device if
it has the wrong path?