linux-kernel - [PATCH] usb: xhci: fix potential divide-by-zero in xhci_urb

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Message-ID: <20260110183421.23758-1-eeodqql09@gmail.com>
Date: Sat, 10 Jan 2026 13:34:21 -0500
From: pip-izony <eeodqql09@...il.com>
To: Mathias Nyman <mathias.nyman@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Seungjin Bae <eeodqql09@...il.com>,
	Kyungtae Kim <Kyungtae.Kim@...tmouth.edu>,
	Reyad Attiyat <reyad.attiyat@...il.com>,
	linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] usb: xhci: fix potential divide-by-zero in xhci_urb_enqueue()

From: Seungjin Bae <eeodqql09@...il.com>

The `xhci_urb_enqueue()` validates Bulk OUT transfers by checking if the
buffer length is a multiple of the packet size. However, it doesn't check
whether the endpoint's `wMaxPacketSize` is zero before using it as a
divisor in a modulo operation.

If a malicious USB device sends a descriptor with `wMaxPacketSize` set to
0, it triggers a divide-by-zero exception (kernel panic). This allows an
attacker with physical access to crash the system, leading to a Denial of
Service.

Fix this by adding a check to ensure `wMaxPacketSize` is greater than 0
before performing the modulo operation.

Fixes: 4758dcd19a7d ("usb: xhci: Add support for URB_ZERO_PACKET to bulk/sg transfers")
Signed-off-by: Seungjin Bae <eeodqql09@...il.com>
---
 drivers/usb/host/xhci.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
index 0cb45b95e4f5..f22ee6cc3083 100644
--- a/drivers/usb/host/xhci.c
+++ b/drivers/usb/host/xhci.c
@@ -1621,15 +1621,18 @@ static int xhci_urb_enqueue(struct usb_hcd *hcd, struct urb *urb, gfp_t mem_flag
 	unsigned int *ep_state;
 	struct urb_priv	*urb_priv;
 	int num_tds;
+	int maxp;
 
 	ep_index = xhci_get_endpoint_index(&urb->ep->desc);
+	maxp = usb_endpoint_maxp(&urb->ep->desc);
 
 	if (usb_endpoint_xfer_isoc(&urb->ep->desc))
 		num_tds = urb->number_of_packets;
 	else if (usb_endpoint_is_bulk_out(&urb->ep->desc) &&
 	    urb->transfer_buffer_length > 0 &&
 	    urb->transfer_flags & URB_ZERO_PACKET &&
-	    !(urb->transfer_buffer_length % usb_endpoint_maxp(&urb->ep->desc)))
+		maxp > 0 &&
+	    !(urb->transfer_buffer_length % maxp))
 		num_tds = 2;
 	else
 		num_tds = 1;
-- 
2.43.0