linux-kernel - [PATCH] HID: core: remove unnecessary WARN

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Date: Fri, 17 May 2024 07:19:14 -0700
From: Nikita Zhandarovich <n.zhandarovich@...tech.ru>
To: Jiri Kosina <jikos@...nel.org>
CC: Nikita Zhandarovich <n.zhandarovich@...tech.ru>, Benjamin Tissoires
	<bentiss@...nel.org>, Dmitry Torokhov <dmitry.torokhov@...il.com>, "Douglas
 Anderson" <dianders@...omium.org>, <linux-input@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Alan Stern <stern@...land.harvard.edu>,
	<syzbot+5186630949e3c55f0799@...kaller.appspotmail.com>
Subject: [PATCH] HID: core: remove unnecessary WARN_ON() in implement()

Syzkaller hit a warning [1] in a call to implement() when trying
to write a value into a field of smaller size in an output report.

Since implement() already has a warn message printed out with the
help of hid_warn() and value in question gets trimmed with:
	...
	value &= m;
	...
WARN_ON may be considered superfluous. Remove it to suppress future
syzkaller triggers.

[1]
WARNING: CPU: 0 PID: 5084 at drivers/hid/hid-core.c:1451 implement drivers/hid/hid-core.c:1451 [inline]
WARNING: CPU: 0 PID: 5084 at drivers/hid/hid-core.c:1451 hid_output_report+0x548/0x760 drivers/hid/hid-core.c:1863
Modules linked in:
CPU: 0 PID: 5084 Comm: syz-executor424 Not tainted 6.9.0-rc7-syzkaller-00183-gcf87f46fd34d #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/02/2024
RIP: 0010:implement drivers/hid/hid-core.c:1451 [inline]
RIP: 0010:hid_output_report+0x548/0x760 drivers/hid/hid-core.c:1863
..
Call Trace:
 <TASK>
 __usbhid_submit_report drivers/hid/usbhid/hid-core.c:591 [inline]
 usbhid_submit_report+0x43d/0x9e0 drivers/hid/usbhid/hid-core.c:636
 hiddev_ioctl+0x138b/0x1f00 drivers/hid/usbhid/hiddev.c:726
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:904 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:890
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
..

Fixes: 95d1c8951e5b ("HID: simplify implement() a bit")
Reported-by: syzbot+5186630949e3c55f0799@...kaller.appspotmail.com
Signed-off-by: Nikita Zhandarovich <n.zhandarovich@...tech.ru>
---
 drivers/hid/hid-core.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
index b1fa0378e8f4..74efda212c55 100644
--- a/drivers/hid/hid-core.c
+++ b/drivers/hid/hid-core.c
@@ -1448,7 +1448,6 @@ static void implement(const struct hid_device *hid, u8 *report,
 			hid_warn(hid,
 				 "%s() called with too large value %d (n: %d)! (%s)\n",
 				 __func__, value, n, current->comm);
-			WARN_ON(1);
 			value &= m;
 		}
 	}