linux-kernel - Re: [PATCH V2] Fix unsafe memory access by memcmp

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Date:   Mon, 04 Apr 2022 16:47:24 +0200
From:   "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Charlie Sands <sandsch@...thvilleschools.net>,
        gregkh@...uxfoundation.org, Larry.Finger@...inger.net,
        phil@...lpotter.co.uk, linux-staging@...ts.linux.dev,
        linux-kernel@...r.kernel.org, paskripkin@...il.com
Subject: Re: [PATCH V2] Fix unsafe memory access by memcmp

On luned? 4 aprile 2022 16:35:31 CEST Dan Carpenter wrote:
> On Mon, Apr 04, 2022 at 04:29:48PM +0200, Fabio M. De Francesco wrote:

> > Is it safe to access user space pointers without using proper helpers? 
> 
> No.
> 
> > In those cases I mean: is it safe without using copy_from_user()?
> 
> Correct.  You need to use copy_from_user().
> 
> > 
> > As I said, perhaps I'm overlooking something. However my conclusions 
> > follow by your own argument.
> > 
> > If I understand what you wrote, you asked to delete rtw_p2p_get()
> > because it looks like nobody "has ever tested or used this code".
> > 
> > rtw_p2p_get2() and rtw_p2p_set() use the same pattern of rtw_p2p_get()
> > when they access user space without using the proper helpers.
> 
> Those functions use "extra" which is a kernel pointer.  Which user
> pointer do they use?  Sparse doesn't detect it.

You're right, sorry. This is what I had overlooked. I took a brief look
(just 5 seconds or something) and saw the same arguments that 
rtw_p2p_get() takes and then a long list of calls to memcmp().

I overlooked that they were called using the 4th argument ("extra").

Sorry for the noise.

Fabio