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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Alan Stern <stern@rowland.harvard.edu>,
        Felipe Balbi <balbi@kernel.org>,
        syzbot+8ab8bf161038a8768553@syzkaller.appspotmail.com
Subject: [PATCH 4.9 38/62] USB: gadget: Reject endpoints with 0 maxpacket value
Date:   Mon,  4 Nov 2019 22:45:00 +0100
Message-Id: <20191104211941.314059122@linuxfoundation.org>
In-Reply-To: <20191104211901.387893698@linuxfoundation.org>
References: <20191104211901.387893698@linuxfoundation.org>
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From: Alan Stern <stern@rowland.harvard.edu>

commit 54f83b8c8ea9b22082a496deadf90447a326954e upstream.

Endpoints with a maxpacket length of 0 are probably useless.  They
can't transfer any data, and it's not at all unlikely that a UDC will
crash or hang when trying to handle a non-zero-length usb_request for
such an endpoint.  Indeed, dummy-hcd gets a divide error when trying
to calculate the remainder of a transfer length by the maxpacket
value, as discovered by the syzbot fuzzer.

Currently the gadget core does not check for endpoints having a
maxpacket value of 0.  This patch adds a check to usb_ep_enable(),
preventing such endpoints from being used.

As far as I know, none of the gadget drivers in the kernel tries to
create an endpoint with maxpacket = 0, but until now there has been
nothing to prevent userspace programs under gadgetfs or configfs from
doing it.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-and-tested-by: syzbot+8ab8bf161038a8768553@syzkaller.appspotmail.com
CC: <stable@vger.kernel.org>
Acked-by: Felipe Balbi <balbi@kernel.org>
Link: https://lore.kernel.org/r/Pine.LNX.4.44L0.1910281052370.1485-100000@iolanthe.rowland.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/usb/gadget/udc/core.c |   11 +++++++++++
 1 file changed, 11 insertions(+)

--- a/drivers/usb/gadget/udc/core.c
+++ b/drivers/usb/gadget/udc/core.c
@@ -106,6 +106,17 @@ int usb_ep_enable(struct usb_ep *ep)
 	if (ep->enabled)
 		goto out;
 
+	/* UDC drivers can't handle endpoints with maxpacket size 0 */
+	if (usb_endpoint_maxp(ep->desc) == 0) {
+		/*
+		 * We should log an error message here, but we can't call
+		 * dev_err() because there's no way to find the gadget
+		 * given only ep.
+		 */
+		ret = -EINVAL;
+		goto out;
+	}
+
 	ret = ep->ops->enable(ep, ep->desc);
 	if (ret)
 		goto out;