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References: <20221123050911.1045190-1-butterflyhuangxx@gmail.com> <87mt8i5fcz.wl-tiwai@suse.de>
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From:   butt3rflyh4ck <butterflyhuangxx@gmail.com>
Date:   Wed, 23 Nov 2022 15:06:16 +0800
Message-ID: <CAFcO6XPoNnM+VzY+bj5sPfJ-tCLQQ_pb8yb90KifWTwVpdENKA@mail.gmail.com>
Subject: Re: [RESEND PATCH] ALSA: rawmidi: fix infoleak in snd_rawmidi_ioctl_status_compat64
To:     Takashi Iwai <tiwai@suse.de>
Cc:     perex@perex.cz, tiwai@suse.com, baolin.wang@linux.alibaba.com,
        alsa-devel@alsa-project.org, linux-kernel@vger.kernel.org
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Hi, the compat_status structure is struct compat_snd_rawmidi_status64 {
s32 stream;
u8 rsvd[4]; /* alignment */
s64 tstamp_sec;
s64 tstamp_nsec;
u32 avail;
u32 xruns;
unsigned char reserved[16];
} __attribute__((packed));
The rsvd[4] and reserved[16] are not  initialized.


Regards,
 butt3rflyh4ck.

On Wed, Nov 23, 2022 at 2:55 PM Takashi Iwai <tiwai@suse.de> wrote:
>
> 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@gmail.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


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