linux-kernel - [PATCH V2] usbip: Fix locking bug in RT-enabled kernels

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Message-ID: <20250916014143.1439759-1-lizhi.xu@windriver.com>
Date: Tue, 16 Sep 2025 09:41:43 +0800
From: Lizhi Xu <lizhi.xu@...driver.com>
To: <stern@...land.harvard.edu>
CC: <gregkh@...uxfoundation.org>, <linux-kernel@...r.kernel.org>,
        <linux-usb@...r.kernel.org>, <lizhi.xu@...driver.com>,
        <syzbot+205ef33a3b636b4181fb@...kaller.appspotmail.com>,
        <syzkaller-bugs@...glegroups.com>
Subject: [PATCH V2] usbip: Fix locking bug in RT-enabled kernels

Interrupts are disabled before entering usb_hcd_giveback_urb().
A spinlock_t becomes a sleeping lock on PREEMPT_RT, so it cannot be
acquired with disabled interrupts.

Save the interrupt status and restore it after usb_hcd_giveback_urb().

syz reported:
BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:48
Call Trace:
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 rt_spin_lock+0xc7/0x2c0 kernel/locking/spinlock_rt.c:57
 spin_lock include/linux/spinlock_rt.h:44 [inline]
 mon_bus_complete drivers/usb/mon/mon_main.c:134 [inline]
 mon_complete+0x5c/0x200 drivers/usb/mon/mon_main.c:147
 usbmon_urb_complete include/linux/usb/hcd.h:738 [inline]
 __usb_hcd_giveback_urb+0x254/0x5e0 drivers/usb/core/hcd.c:1647
 vhci_urb_enqueue+0xb4f/0xe70 drivers/usb/usbip/vhci_hcd.c:818

Reported-by: syzbot+205ef33a3b636b4181fb@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=205ef33a3b636b4181fb
Signed-off-by: Lizhi Xu <lizhi.xu@...driver.com>
---
V1 -> V2: fix it in usbip

 drivers/usb/usbip/vhci_hcd.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/usbip/vhci_hcd.c b/drivers/usb/usbip/vhci_hcd.c
index e70fba9f55d6..eb6de7e8ea7b 100644
--- a/drivers/usb/usbip/vhci_hcd.c
+++ b/drivers/usb/usbip/vhci_hcd.c
@@ -809,15 +809,15 @@ static int vhci_urb_enqueue(struct usb_hcd *hcd, struct urb *urb, gfp_t mem_flag
 no_need_xmit:
 	usb_hcd_unlink_urb_from_ep(hcd, urb);
 no_need_unlink:
-	spin_unlock_irqrestore(&vhci->lock, flags);
 	if (!ret) {
 		/* usb_hcd_giveback_urb() should be called with
 		 * irqs disabled
 		 */
-		local_irq_disable();
+		spin_unlock(&vhci->lock);
 		usb_hcd_giveback_urb(hcd, urb, urb->status);
-		local_irq_enable();
+		spin_lock(&vhci->lock);
 	}
+	spin_unlock_irqrestore(&vhci->lock, flags);
 	return ret;
 }
 
-- 
2.43.0