linux-kernel - [PATCH] usb: atm: cxacru: fix a flaw in existing endpoint checks

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Message-ID: <20250213122259.730772-1-n.zhandarovich@fintech.ru>
Date: Thu, 13 Feb 2025 15:22:57 +0300
From: Nikita Zhandarovich <n.zhandarovich@...tech.ru>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC: Nikita Zhandarovich <n.zhandarovich@...tech.ru>,
	<accessrunner-general@...ts.sourceforge.net>, <linux-usb@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>,
	<syzbot+ccbbc229a024fa3e13b5@...kaller.appspotmail.com>,
	<syzkaller-bugs@...glegroups.com>
Subject: [PATCH] usb: atm: cxacru: fix a flaw in existing endpoint checks

Syzbot once again identified a flaw in usb endpoint checking, see [1].
This time the issue stems from a commit authored by me (2eabb655a968
("usb: atm: cxacru: fix endpoint checking in cxacru_bind()")).

While using usb_find_common_endpoints() may usually be enough to
discard devices with wrong endpoints, in this case one needs more
than just finding and identifying the sufficient number of endpoints
of correct types - one needs to check the endpoint's address as well.

Since cxacru_bind() fills URBs with CXACRU_EP_CMD address in mind,
switch the endpoint verification approach to usb_check_XXX_endpoints()
instead to fix incomplete ep testing.

[1] Syzbot report:
usb 5-1: BOGUS urb xfer, pipe 3 != type 1
WARNING: CPU: 0 PID: 1378 at drivers/usb/core/urb.c:504 usb_submit_urb+0xc4e/0x18c0 drivers/usb/core/urb.c:503
...
RIP: 0010:usb_submit_urb+0xc4e/0x18c0 drivers/usb/core/urb.c:503
...
Call Trace:
 <TASK>
 cxacru_cm+0x3c8/0xe50 drivers/usb/atm/cxacru.c:649
 cxacru_card_status drivers/usb/atm/cxacru.c:760 [inline]
 cxacru_bind+0xcf9/0x1150 drivers/usb/atm/cxacru.c:1223
 usbatm_usb_probe+0x314/0x1d30 drivers/usb/atm/usbatm.c:1058
 cxacru_usb_probe+0x184/0x220 drivers/usb/atm/cxacru.c:1377
 usb_probe_interface+0x641/0xbb0 drivers/usb/core/driver.c:396
 really_probe+0x2b9/0xad0 drivers/base/dd.c:658
 __driver_probe_device+0x1a2/0x390 drivers/base/dd.c:800
 driver_probe_device+0x50/0x430 drivers/base/dd.c:830
...

Reported-and-tested-by: syzbot+ccbbc229a024fa3e13b5@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=ccbbc229a024fa3e13b5
Fixes: 2eabb655a968 ("usb: atm: cxacru: fix endpoint checking in cxacru_bind()")
Cc: stable@...nel.org
Signed-off-by: Nikita Zhandarovich <n.zhandarovich@...tech.ru>
---
P.S. another option would be to try to use endpoints found by
usb_find_common_endpoints() and use them to fill and send URBs.
But this may interfere with real devices and I have no way of
testing them myself.

 drivers/usb/atm/cxacru.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/drivers/usb/atm/cxacru.c b/drivers/usb/atm/cxacru.c
index 0dd85d2635b9..47d06af33747 100644
--- a/drivers/usb/atm/cxacru.c
+++ b/drivers/usb/atm/cxacru.c
@@ -1131,7 +1131,10 @@ static int cxacru_bind(struct usbatm_data *usbatm_instance,
 	struct cxacru_data *instance;
 	struct usb_device *usb_dev = interface_to_usbdev(intf);
 	struct usb_host_endpoint *cmd_ep = usb_dev->ep_in[CXACRU_EP_CMD];
-	struct usb_endpoint_descriptor *in, *out;
+	static const u8 ep_addrs[] = {
+		CXACRU_EP_CMD + USB_DIR_IN,
+		CXACRU_EP_CMD + USB_DIR_OUT,
+		0};
 	int ret;

 	/* instance init */
@@ -1179,13 +1182,11 @@ static int cxacru_bind(struct usbatm_data *usbatm_instance,
 	}

 	if (usb_endpoint_xfer_int(&cmd_ep->desc))
-		ret = usb_find_common_endpoints(intf->cur_altsetting,
-						NULL, NULL, &in, &out);
+		ret = usb_check_int_endpoints(intf, ep_addrs);
 	else
-		ret = usb_find_common_endpoints(intf->cur_altsetting,
-						&in, &out, NULL, NULL);
+		ret = usb_check_bulk_endpoints(intf, ep_addrs);

-	if (ret) {
+	if (!ret) {
 		usb_err(usbatm_instance, "cxacru_bind: interface has incorrect endpoints\n");
 		ret = -ENODEV;
 		goto fail;