linux-kernel - [PATCH v3] thunderbolt: For dev authorization changes, include the actual event in udev change notification

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Message-Id: <20210730235304.3179882-1-rajatja@google.com>
Date:   Fri, 30 Jul 2021 16:53:04 -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,
        gregkh@...uxfoundation.org
Cc:     Rajat Jain <rajatja@...gle.com>, rajatxjain@...il.com
Subject: [PATCH v3] thunderbolt: For dev authorization changes, include the
 actual event in udev change notification

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>
---
v3: rearrange the local variable definitions, add comments
v2: Commit log changes

 drivers/thunderbolt/switch.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/thunderbolt/switch.c b/drivers/thunderbolt/switch.c
index 83b1ef3d5d03..dc2005bbd682 100644
--- a/drivers/thunderbolt/switch.c
+++ b/drivers/thunderbolt/switch.c
@@ -1498,6 +1498,7 @@ static ssize_t authorized_show(struct device *dev,
 
 static int disapprove_switch(struct device *dev, void *not_used)
 {
+	char *envp[] = { "AUTHORIZED=0", NULL };
 	struct tb_switch *sw;
 
 	sw = tb_to_switch(dev);
@@ -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;
@@ -1522,7 +1523,9 @@ static int disapprove_switch(struct device *dev, void *not_used)
 
 static int tb_switch_set_authorized(struct tb_switch *sw, unsigned int val)
 {
+	char envp_string[13];
 	int ret = -EINVAL;
+	char *envp[] = { envp_string, NULL };
 
 	if (!mutex_trylock(&sw->tb->lock))
 		return restart_syscall();
@@ -1559,8 +1562,12 @@ 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);
+		/*
+		 * Notify status change to the userspace, informing the new
+		 * value of /sys/bus/thunderbolt/devices/.../authorized
+		 */
+		sprintf(envp_string, "AUTHORIZED=%u", sw->authorized);
+		kobject_uevent_env(&sw->dev.kobj, KOBJ_CHANGE, envp);
 	}
 
 unlock:
-- 
2.32.0.554.ge1b32706d8-goog