linux-kernel - Re: [PATCH] arch: mips: sibyte: Return -EFAULT if copy_to

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Date:   Mon, 1 Mar 2021 23:01:49 +0100 (CET)
From:   "Maciej W. Rozycki" <macro@...am.me.uk>
To:     Sergei Shtylyov <sergei.shtylyov@...il.com>
cc:     Wang Qing <wangqing@...o.com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arch: mips: sibyte: Return -EFAULT if copy_to_user()
 fails

On Mon, 1 Mar 2021, Sergei Shtylyov wrote:

> > The copy_to_user() function returns the number of bytes remaining to be
> > copied, but we want to return -EFAULT if the copy doesn't complete.
> 
>    Then 'err' is hardly a good name for that variable. :-)

 Something like `left' might be better, especially as it's the sole use.  
Also it's been like this from the beginning, so:

Fixes: bb9b813bb665 ("[MIPS] Sibyte: Fix ZBbus profiler")

or maybe:

Fixes: d619f38fdacb ("[MIPS] Add bcm1480 ZBus trace support, fix wait related bugs")

(since the file was renamed from a different name with the latter commit) 
would I think be helpful for backports too.  It looks like potentially 
quite a nasty bug to me if someone actually uses this piece (I haven't).

  Maciej