Re: [PATCH] Input: uinput - fix Spectre v1 vulnerability

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

On October 16, 2018 10:52:58 AM PDT, "Gustavo A. R. Silva" <gustavo@embeddedor.com> wrote:
>Hi Dmitry,
>
>On 10/16/18 7:21 PM, Dmitry Torokhov wrote:
>> Hi Gustavo,
>> 
>> On Tue, Oct 16, 2018 at 01:13:13PM +0200, Gustavo A. R. Silva wrote:
>>> setup.code can be indirectly controlled by user-space, hence leading
>to
>>> a potential exploitation of the Spectre variant 1 vulnerability.
>>>
>>> This issue was detected with the help of Smatch:
>>>
>>> drivers/input/misc/uinput.c:512 uinput_abs_setup() warn: potential
>>> spectre issue 'dev->absinfo' [w] (local cap)
>>>
>>> Fix this by sanitizing setup.code before using it to index
>dev->absinfo.
>> 
>> So we are saying that attacker, by repeatedly calling ioctl(...,
>> UI_ABS_SETUP, ...) will be able to poison branch predictor and
>discover
>> another program or kernel secrets? But uinput is a privileged
>interface
>> open to root only, as it allows injecting arbitrary keystrokes into
>the
>> kernel. And since only root can use uinput, meh?
>> 
>
>Oh I see... in that case this is a false positive.
>
>Although, I wonder if all these operations are only accessible to root:
>
>static const struct file_operations uinput_fops = {
>        .owner          = THIS_MODULE,
>        .open           = uinput_open,
>        .release        = uinput_release,
>        .read           = uinput_read,
>        .write          = uinput_write,
>        .poll           = uinput_poll,
>        .unlocked_ioctl = uinput_ioctl,
>#ifdef CONFIG_COMPAT
>        .compat_ioctl   = uinput_compat_ioctl,
>#endif
>        .llseek         = no_llseek,
>};

/dev/uinput must be 0600, or accessible to equally privileged user, or you'll be opening your system to much mischief.


Thanks.

-- 
Dmitry