HID: hidraw, uhid: Always report EPOLLOUT

BugLink: https://bugs.launchpad.net/bugs/1860681

[ Upstream commit 9e635c28 ]

hidraw and uhid device nodes are always available for writing so we should
always report EPOLLOUT and EPOLLWRNORM bits, not only in the cases when
there is nothing to read.
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Fixes: be54e746 ("HID: uhid: Fix returning EPOLLOUT from uhid_char_poll")
Fixes: 9f3b61dc ("HID: hidraw: Fix returning EPOLLOUT from hidraw_poll")
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Connor Kuehl <connor.kuehl@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

drivers/hid/hidraw.c

@@ -262,13 +262,14 @@ static ssize_t hidraw_get_report(struct file *file, char __user *buffer, size_t
 static unsigned int hidraw_poll(struct file *file, poll_table *wait)
 {
 	struct hidraw_list *list = file->private_data;
+	unsigned int mask = POLLOUT | POLLWRNORM; /* hidraw is always writable */
 
 	poll_wait(file, &list->hidraw->wait, wait);
 	if (list->head != list->tail)
-		return POLLIN | POLLRDNORM;
+		mask |= POLLIN | POLLRDNORM;
 	if (!list->hidraw->exist)
-		return POLLERR | POLLHUP;
-	return POLLOUT | POLLWRNORM;
+		mask |= POLLERR | POLLHUP;
+	return mask;
 }
 
 static int hidraw_open(struct inode *inode, struct file *file)

drivers/hid/uhid.c

@@ -769,13 +769,14 @@ static ssize_t uhid_char_write(struct file *file, const char __user *buffer,
 static unsigned int uhid_char_poll(struct file *file, poll_table *wait)
 {
 	struct uhid_device *uhid = file->private_data;
+	unsigned int mask = POLLOUT | POLLWRNORM; /* uhid is always writable */
 
 	poll_wait(file, &uhid->waitq, wait);
 
 	if (uhid->head != uhid->tail)
-		return POLLIN | POLLRDNORM;
+		mask |= POLLIN | POLLRDNORM;
 
-	return EPOLLOUT | EPOLLWRNORM;
+	return mask;
 }
 
 static const struct file_operations uhid_fops = {