linux-kernel - Re: [PATCH][next] ALSA: vmaster: Use flex_array

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Date:   Thu, 30 Jul 2020 16:57:51 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc:     "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] ALSA: vmaster: Use flex_array_size() helper in memcpy()

On Thu, 30 Jul 2020 15:12:33 +0200,
Gustavo A. R. Silva wrote:
> 
> 
> 
> On 7/30/20 03:41, Takashi Iwai wrote:
> > On Thu, 30 Jul 2020 00:18:29 +0200,
> > Gustavo A. R. Silva wrote:
> >>
> >> Make use of the flex_array_size() helper to calculate the size of a
> >> flexible array member within an enclosing structure.
> >>
> >> This helper offers defense-in-depth against potential integer overflows
> >> and makes it explicitly clear that we are dealing with a flexible array
> >> member.
> >>
> >> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> >> ---
> >>  sound/core/vmaster.c | 3 ++-
> >>  1 file changed, 2 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/sound/core/vmaster.c b/sound/core/vmaster.c
> >> index ab36f9898711..21ce4082cb5f 100644
> >> --- a/sound/core/vmaster.c
> >> +++ b/sound/core/vmaster.c
> >> @@ -262,7 +262,8 @@ int _snd_ctl_add_follower(struct snd_kcontrol *master,
> >>  		return -ENOMEM;
> >>  	srec->kctl = follower;
> >>  	srec->follower = *follower;
> >> -	memcpy(srec->follower.vd, follower->vd, follower->count * sizeof(*follower->vd));
> >> +	memcpy(srec->follower.vd, follower->vd, flex_array_size(srec, follower.vd,
> >> +								srec->follower.count));
> > 
> > Changing from follower->count to srec->follower.count isn't obvious,
> > so it should have been mentioned in the log; other than that, the code
> > change looks good.
> > 
> 
> Yeah; you're right. I'll include that in the changelog text.

OK, then I'll wait for the v2 for merging.

> > But since the API isn't in Linus tree yet, I'll postpone the merge
> > until the API reaches to upstream.  Maybe I can merge this during RC1
> > merge window, as those are trivial.
> > 
> 
> The API is already in mainline, see:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/linux/overflow.h#n320

Ah, thanks, I didn't expect that the API change comes after rc1 into
mainline.  Then I can merge later the commits based on the late rc.


Takashi