Re: [Linux-kernel-mentees] [PATCH] net: usb: Fix uninit-was-stored issue in asix_read_cmd()

[Dmitry Vyukov via Linux-kernel-mentees <linux-kernel-mentees@lists.linuxfoundation.org>]

On Sun, Aug 23, 2020 at 10:21 AM Himadri Pandya
<himadrispandya@gmail.com> wrote:
>
> Initialize the buffer before passing it to usb_read_cmd() function(s) to
> fix the uninit-was-stored issue in asix_read_cmd().
>
> Fixes: KMSAN: kernel-infoleak in raw_ioctl
> Reported by: syzbot+a7e220df5a81d1ab400e@syzkaller.appspotmail.com
>
> Signed-off-by: Himadri Pandya <himadrispandya@gmail.com>
> ---
>  drivers/net/usb/asix_common.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/net/usb/asix_common.c b/drivers/net/usb/asix_common.c
> index e39f41efda3e..a67ea1971b78 100644
> --- a/drivers/net/usb/asix_common.c
> +++ b/drivers/net/usb/asix_common.c
> @@ -17,6 +17,8 @@ int asix_read_cmd(struct usbnet *dev, u8 cmd, u16 value, u16 index,
>
>         BUG_ON(!dev);
>
> +       memset(data, 0, size);

Hi Himadri,

I think the proper fix is to check
usbnet_read_cmd/usbnet_read_cmd_nopm return value instead.
Memsetting data helps to fix the warning at hand, but the device did
not send these 0's and we use them as if the device did send them.

Perhaps we need a separate helper function (of a bool flag) that will
fail on incomplete reads. Maybe even in the common USB layer because I
think we've seen this type of bug lots of times and I guess there are
dozens more.


>         if (!in_pm)
>                 fn = usbnet_read_cmd;
>         else
> --
> 2.17.1
>
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