linux-kernel - Re: [PATCH] ALSA: control: fix a redundant-copy issue

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Date:   Sun, 13 May 2018 09:06:26 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     "Wenwen Wang" <wang6495@....edu>
Cc:     "moderated list:SOUND" <alsa-devel@...a-project.org>,
        "Jaroslav Kysela" <perex@...ex.cz>, "Kangjie Lu" <kjlu@....edu>,
        "open list" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ALSA: control: fix a redundant-copy issue

On Sat, 05 May 2018 20:38:03 +0200,
Wenwen Wang wrote:
> 
> In snd_ctl_elem_add_compat(), the fields of the struct 'data' need to be
> copied from the corresponding fields of the struct 'data32' in userspace.
> This is achieved by invoking copy_from_user() and get_user() functions. The
> problem here is that the 'type' field is copied twice. One is by
> copy_from_user() and one is by get_user(). Given that the 'type' field is
> not used between the two copies, the second copy is *completely* redundant
> and should be removed for better performance and cleanup. Also, these two
> copies can cause inconsistent data: as the struct 'data32' resides in
> userspace and a malicious userspace process can race to change the 'type'
> field between the two copies to cause inconsistent data. Depending on how
> the data is used in the future, such an inconsistency may cause potential
> security risks.
> 
> For above reasons, we should take out the second copy.
> 
> Signed-off-by: Wenwen Wang <wang6495@....edu>

Applied now, thanks.


Takashi