Input: uinput - allow injecting event times

Currently, uinput doesn't use the input_set_timestamp API, so any
event injected using uinput is not accurately timestamped in terms of
measuring when the actual event happened. Hence, call the
input_set_timestamp API from uinput in order to provide a more
accurate sense of time for the event. Propagate only the timestamps
which are a) positive, b) within a pre-defined offset (10 secs) from
the current time, and c) not in the future.

Signed-off-by: Biswarup Pal <[e-mail]>
Reviewed-by: Peter Hutterer <[e-mail]>
Reviewed-by: Siarhei Vishniakou <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Dmitry Torokhov <[e-mail]>

drivers/input/misc/uinput.c

···
 #define UINPUT_NAME		"uinput"
 #define UINPUT_BUFFER_SIZE	16
 #define UINPUT_NUM_REQUESTS	16
+#define UINPUT_TIMESTAMP_ALLOWED_OFFSET_SECS 10
 
 enum uinput_state { UIST_NEW_DEVICE, UIST_SETUP_COMPLETE, UIST_CREATED };
 
···
 	return retval;
 }
 
+/*
+ * Returns true if the given timestamp is valid (i.e., if all the following
+ * conditions are satisfied), false otherwise.
+ * 1) given timestamp is positive
+ * 2) it's within the allowed offset before the current time
+ * 3) it's not in the future
+ */
+static bool is_valid_timestamp(const ktime_t timestamp)
+{
+	ktime_t zero_time;
+	ktime_t current_time;
+	ktime_t min_time;
+	ktime_t offset;
+
+	zero_time = ktime_set(0, 0);
+	if (ktime_compare(zero_time, timestamp) >= 0)
+		return false;
+
+	current_time = ktime_get();
+	offset = ktime_set(UINPUT_TIMESTAMP_ALLOWED_OFFSET_SECS, 0);
+	min_time = ktime_sub(current_time, offset);
+
+	if (ktime_after(min_time, timestamp) || ktime_after(timestamp, current_time))
+		return false;
+
+	return true;
+}
+
 static ssize_t uinput_inject_events(struct uinput_device *udev,
 				    const char __user *buffer, size_t count)
 {
 	struct input_event ev;
 	size_t bytes = 0;
+	ktime_t timestamp;
 
 	if (count != 0 && count < input_event_size())
 		return -EINVAL;
···
 		 */
 		if (input_event_from_user(buffer + bytes, &ev))
 			return -EFAULT;
+
+		timestamp = ktime_set(ev.input_event_sec, ev.input_event_usec * NSEC_PER_USEC);
+		if (is_valid_timestamp(timestamp))
+			input_set_timestamp(udev->dev, timestamp);
 
 		input_event(udev->dev, ev.type, ev.code, ev.value);
 		bytes += input_event_size();