[PATCH AUTOSEL 4.19] Input: MT - limit max slots

[Sasha Levin <sashal@kernel.org>]

From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>

[ Upstream commit 99d3bf5f7377d42f8be60a6b9cb60fb0be34dceb ]

syzbot is reporting too large allocation at input_mt_init_slots(), for
num_slots is supplied from userspace using ioctl(UI_DEV_CREATE).

Since nobody knows possible max slots, this patch chose 1024.

Reported-by: syzbot <syzbot+0122fa359a69694395d5@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=0122fa359a69694395d5
Suggested-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/input/input-mt.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/input/input-mt.c b/drivers/input/input-mt.c
index 6c7326c93721c..fd01c9306e66c 100644
--- a/drivers/input/input-mt.c
+++ b/drivers/input/input-mt.c
@@ -48,6 +48,9 @@ int input_mt_init_slots(struct input_dev *dev, unsigned int num_slots,
 		return 0;
 	if (mt)
 		return mt->num_slots != num_slots ? -EINVAL : 0;
+	/* Arbitrary limit for avoiding too large memory allocation. */
+	if (num_slots > 1024)
+		return -EINVAL;
 
 	mt = kzalloc(struct_size(mt, slots, num_slots), GFP_KERNEL);
 	if (!mt)
-- 
2.43.0