linux-kernel - Re: [PATCH v2] thunderbolt: For dev authorization changes, include the actual event in udev change notification

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Date:   Fri, 23 Jul 2021 17:41:58 -0700
From:   Rajat Jain <rajatja@...gle.com>
To:     Andreas Noever <andreas.noever@...il.com>,
        Michael Jamet <michael.jamet@...el.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Yehezkel Bernat <yehezkelshb@...il.com>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     rajatxjain@...il.com
Subject: Re: [PATCH v2] thunderbolt: For dev authorization changes, include
 the actual event in udev change notification

(fixing the typo in the email ID for Greg).

On Fri, Jul 23, 2021 at 5:40 PM Rajat Jain <rajatja@...gle.com> wrote:
>
> For security, we would like to monitor and track when the thunderbolt
> devices are authorized and deauthorized (i.e. when the thunderbolt sysfs
> "authorized" attribute changes). Currently the userspace gets a udev
> change notification when there is a change, but the state may have
> changed (again) by the time we look at the authorized attribute in
> sysfs. So an authorization event may go unnoticed. Thus make it easier
> by informing the actual change (new value of authorized attribute) in
> the udev change notification.
>
> The change is included as a key value "authorized=<val>" where <val>
> is the new value of sysfs attribute "authorized", and is described at
> Documentation/ABI/testing/sysfs-bus-thunderbolt under
> /sys/bus/thunderbolt/devices/.../authorized
>
> Signed-off-by: Rajat Jain <rajatja@...gle.com>
> ---
>  drivers/thunderbolt/switch.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/thunderbolt/switch.c b/drivers/thunderbolt/switch.c
> index 83b1ef3d5d03..382128dfbdee 100644
> --- a/drivers/thunderbolt/switch.c
> +++ b/drivers/thunderbolt/switch.c
> @@ -1499,6 +1499,7 @@ static ssize_t authorized_show(struct device *dev,
>  static int disapprove_switch(struct device *dev, void *not_used)
>  {
>         struct tb_switch *sw;
> +       char *envp[] = { "AUTHORIZED=0", NULL };
>
>         sw = tb_to_switch(dev);
>         if (sw && sw->authorized) {
> @@ -1514,7 +1515,7 @@ static int disapprove_switch(struct device *dev, void *not_used)
>                         return ret;
>
>                 sw->authorized = 0;
> -               kobject_uevent(&sw->dev.kobj, KOBJ_CHANGE);
> +               kobject_uevent_env(&sw->dev.kobj, KOBJ_CHANGE, envp);
>         }
>
>         return 0;
> @@ -1523,6 +1524,8 @@ static int disapprove_switch(struct device *dev, void *not_used)
>  static int tb_switch_set_authorized(struct tb_switch *sw, unsigned int val)
>  {
>         int ret = -EINVAL;
> +       char envp_string[13];
> +       char *envp[] = { envp_string, NULL };
>
>         if (!mutex_trylock(&sw->tb->lock))
>                 return restart_syscall();
> @@ -1560,7 +1563,8 @@ static int tb_switch_set_authorized(struct tb_switch *sw, unsigned int val)
>         if (!ret) {
>                 sw->authorized = val;
>                 /* Notify status change to the userspace */
> -               kobject_uevent(&sw->dev.kobj, KOBJ_CHANGE);
> +               sprintf(envp_string, "AUTHORIZED=%u", sw->authorized);
> +               kobject_uevent_env(&sw->dev.kobj, KOBJ_CHANGE, envp);
>         }
>
>  unlock:
> --
> 2.32.0.432.gabb21c7263-goog
>