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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Mon, 27 Jul 2020 17:35:12 +0200
Message-ID: <CAK8P3a3zz-xfz2jwUpEU5R7GyCK735PFQK7OjFmmTESgnSzq=Q@mail.gmail.com>
Subject: Re: [Linux-kernel-mentees] [PATCH] firewire: Prevent kernel-infoleak
 in ioctl_get_info()
To:     Peilin Ye <yepeilin.cs@gmail.com>
Cc:     Stefan Richter <stefanr@s5r6.in-berlin.de>,
        Dan Carpenter <dan.carpenter@oracle.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel-mentees@lists.linuxfoundation.org,
        linux1394-devel@lists.sourceforge.net,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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On Mon, Jul 27, 2020 at 5:18 PM Peilin Ye <yepeilin.cs@gmail.com> wrote:
>
> ioctl_get_info() is copying uninitialized stack memory to userspace due to
> the compiler not initializing holes in statically allocated structures.
> Fix it by initializing `event` using memset() in fill_bus_reset_event().
>
> Cc: stable@vger.kernel.org
> Suggested-by: Dan Carpenter <dan.carpenter@oracle.com>
> Suggested-by: Arnd Bergmann <arnd@arndb.de>
> Signed-off-by: Peilin Ye <yepeilin.cs@gmail.com>

Acked-by: Arnd Bergmann <arnd@arndb.de>

I would recommend always looking through the git history of the
file to come up with an appropriate 'Fixes' tag. In this case

$ git log -p --follow drivers/firewire/core-cdev.c

searching for any mention of fill_bus_reset_event leads you to
commit 344bbc4de14e.

In my ~/.gitconfig I have this alias:

[core]
        abbrev = 12
[alias]
        fixes = show --format='Fixes: %h (\"%s\")' -s

With something like that, calling 'git fixes 344bbc4de14e' produces
the line to copy:

Fixes: 344bbc4de14e ("firewire: Generalize get_config_rom to get_info.")

     Arnd

> ---
>  drivers/firewire/core-cdev.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/firewire/core-cdev.c b/drivers/firewire/core-cdev.c
> index fb6c651214f3..2341d762df5b 100644
> --- a/drivers/firewire/core-cdev.c
> +++ b/drivers/firewire/core-cdev.c
> @@ -340,6 +340,8 @@ static void fill_bus_reset_event(struct fw_cdev_event_bus_reset *event,
>  {
>         struct fw_card *card = client->device->card;
>
> +       memset(event, 0, sizeof(*event));
> +
>         spin_lock_irq(&card->lock);
>
>         event->closure       = client->bus_reset_closure;
> --
> 2.25.1
>