linux-kernel - Re: [PATCH] zram: restrict add/remove attributes to root only

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Message-ID: <20161204105208.GA592@tigerII.localdomain>
Date:   Sun, 4 Dec 2016 19:52:08 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Minchan Kim <minchan@...nel.org>,
        Steven Allen <steven@...balien.com>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [PATCH] zram: restrict add/remove attributes to root only

On (12/04/16 11:28), Greg KH wrote:
> On Sun, Dec 04, 2016 at 11:35:15AM +0900, Sergey Senozhatsky wrote:
[..]

> Why can't a normal user read the attribute?  Does a read actually modify
> something?

yes, it does.

reading from a hot_add file creates a new zram device and returns a new
device's device_id. not initialized device (so it does not eat the memory
for handle table, etc.), but with its own set of sysfs attrs, etc. which
consumes memory after all. so a 'normal' user, doing a simple read from a
hot_add file in a loop just for fun, can create a lot of devices and,
quite likely, cause some troubles (as reported by Steven Allen).

	-ss