linux-kernel - [PATCH 4.4 35/43] USB: Skip endpoints with 0 maxpacket length

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Date:   Mon, 11 Nov 2019 19:28:49 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Alan Stern <stern@...land.harvard.edu>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.4 35/43] USB: Skip endpoints with 0 maxpacket length

From: Alan Stern <stern@...land.harvard.edu>

[ Upstream commit d482c7bb0541d19dea8bff437a9f3c5563b5b2d2 ]

Endpoints with a maxpacket length of 0 are probably useless.  They
can't transfer any data, and it's not at all unlikely that an HCD will
crash or hang when trying to handle an URB for such an endpoint.

Currently the USB core does not check for endpoints having a maxpacket
value of 0.  This patch adds a check, printing a warning and skipping
over any endpoints it catches.

Now, the USB spec does not rule out endpoints having maxpacket = 0.
But since they wouldn't have any practical use, there doesn't seem to
be any good reason for us to accept them.

Signed-off-by: Alan Stern <stern@...land.harvard.edu>

Link: https://lore.kernel.org/r/Pine.LNX.4.44L0.1910281050420.1485-100000@iolanthe.rowland.org
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/usb/core/config.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/usb/core/config.c b/drivers/usb/core/config.c
index 5abc4e5434ecf..cbd064fae23bd 100644
--- a/drivers/usb/core/config.c
+++ b/drivers/usb/core/config.c
@@ -314,6 +314,11 @@ static int usb_parse_endpoint(struct device *ddev, int cfgno, int inum,
 
 	/* Validate the wMaxPacketSize field */
 	maxp = usb_endpoint_maxp(&endpoint->desc);
+	if (maxp == 0) {
+		dev_warn(ddev, "config %d interface %d altsetting %d endpoint 0x%X has wMaxPacketSize 0, skipping\n",
+		    cfgno, inum, asnum, d->bEndpointAddress);
+		goto skip_to_next_endpoint_or_interface_descriptor;
+	}
 
 	/* Find the highest legal maxpacket size for this endpoint */
 	i = 0;		/* additional transactions per microframe */
-- 
2.20.1