linux-kernel - Re: [RESEND PATCH] ALSA: rawmidi: fix infoleak in snd_rawmidi_ioctl_status

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Date:   Wed, 23 Nov 2022 07:55:56 +0100
From:   Takashi Iwai <tiwai@...e.de>
To:     Xiaolong Huang <butterflyhuangxx@...il.com>
Cc:     perex@...ex.cz, tiwai@...e.com, baolin.wang@...ux.alibaba.com,
        alsa-devel@...a-project.org, linux-kernel@...r.kernel.org
Subject: Re: [RESEND PATCH] ALSA: rawmidi: fix infoleak in snd_rawmidi_ioctl_status_compat64

On Wed, 23 Nov 2022 06:09:11 +0100,
Xiaolong Huang wrote:
> 
> The compat_status is declared off of the stack, so it needs to
> be zeroed out before copied back to userspace to prevent any
> unintentional data leakage.
> 
> Fixes: d9e5582c4bb2 ("ALSA: Avoid using timespec for struct snd_rawmidi_status")
> Signed-off-by: Xiaolong Huang <butterflyhuangxx@...il.com>
> 
> ---
> 
> Reason for resend:
> 1. add Fixes line.
> ---
>  sound/core/rawmidi_compat.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/sound/core/rawmidi_compat.c b/sound/core/rawmidi_compat.c
> index 68a93443583c..6afa68165b17 100644
> --- a/sound/core/rawmidi_compat.c
> +++ b/sound/core/rawmidi_compat.c
> @@ -80,6 +80,7 @@ static int snd_rawmidi_ioctl_status_compat64(struct snd_rawmidi_file *rfile,
>  	if (err < 0)
>  		return err;
>  
> +	memset(&compat_status, 0, sizeof(compat_status));
>  	compat_status = (struct compat_snd_rawmidi_status64) {
>  		.stream = status.stream,
>  		.tstamp_sec = status.tstamp_sec,

Here at the line just after your addition, compat_status is fully
initialized by substitution, so I believe the memset is superfluous.

Or have you verified that it really leaks the uninitialized memory?


thanks,

Takashi