[PATCH 6.12.y] Input: always accept EV_SYN in input_event()

[Sasha Levin <sashal@kernel.org>]

From: Dmitry Torokhov <dmitry.torokhov@gmail.com>

[ Upstream commit c1d13bfdb9c75c2885d10332174a887349eb0b51 ]

Commit 0cd587735205 ("Input: preallocate memory to hold event values")
moved allocation of dev->vals into input_allocate_device(), which caused
input core to accumulate events reported while seeding initial device
state before input_register_device().

However, because EV_SYN is only set in dev->evbit during
input_register_device() (and some drivers also overwrite dev->evbit
directly before registration), any EV_SYN/SYN_REPORT events sent before
registration were dropped by is_event_supported(), leaving those seeded
events stuck in dev->vals until the next SYN_REPORT after registration.

Always accept EV_SYN in input_event() and input_inject_event() without
checking dev->evbit so input_sync() flushes dev->vals as intended.

Reported-by: Karlos Abel <kabel@voidship.net>,
Fixes: 0cd587735205 ("Input: preallocate memory to hold event values")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Acked-by: Jiri Kosina <jkosina@suse.com>
Link: https://patch.msgid.link/asx50uz6iafsyAd5@google.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
[ sashal: Adjusted context to preserve explicit spinlock and RCU calls instead of upstream scoped locking guards. ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/input/input.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/input/input.c b/drivers/input/input.c
index c51858f1cdc55..05366b82f722e 100644
--- a/drivers/input/input.c
+++ b/drivers/input/input.c
@@ -392,7 +392,7 @@ void input_event(struct input_dev *dev,
 {
 	unsigned long flags;
 
-	if (is_event_supported(type, dev->evbit, EV_MAX)) {
+	if (type == EV_SYN || is_event_supported(type, dev->evbit, EV_MAX)) {
 
 		spin_lock_irqsave(&dev->event_lock, flags);
 		input_handle_event(dev, type, code, value);
@@ -419,7 +419,7 @@ void input_inject_event(struct input_handle *handle,
 	struct input_handle *grab;
 	unsigned long flags;
 
-	if (is_event_supported(type, dev->evbit, EV_MAX)) {
+	if (type == EV_SYN || is_event_supported(type, dev->evbit, EV_MAX)) {
 		spin_lock_irqsave(&dev->event_lock, flags);
 
 		rcu_read_lock();
-- 
2.53.0