[PATCH 1/2] usbip: drain remaining PDU payload on rejected endpoint

[Sascha Grunert <sgrunert@redhat.com>]

When get_pipe() returns -1, stub_recv_cmd_submit() bails out without
reading the transfer buffer and ISO descriptors that follow the PDU
header on the TCP stream. The next recv() parses leftover payload as a
PDU header, desyncs the stream, and kills the connection.

Consume those trailing bytes before the early return so the stream
stays in sync.

Fixes: 635f545a7e8b ("usbip: fix stub_rx: get_pipe() to validate endpoint number")
Cc: stable@vger.kernel.org
Signed-off-by: Sascha Grunert <sgrunert@redhat.com>
---
 drivers/usb/usbip/stub_rx.c | 60 ++++++++++++++++++++++++++++++++++++-
 1 file changed, 59 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/usbip/stub_rx.c b/drivers/usb/usbip/stub_rx.c
index 1e9ae57..d0e3d3f 100644
--- a/drivers/usb/usbip/stub_rx.c
+++ b/drivers/usb/usbip/stub_rx.c
@@ -461,6 +461,62 @@ static int stub_recv_xbuff(struct usbip_device *ud, struct stub_priv *priv)
 	return ret;
 }
 
+/*
+ * When get_pipe() rejects an endpoint (e.g. an isochronous endpoint that
+ * does not exist in the current alt setting), the transfer buffer and ISO
+ * packet descriptors that follow the PDU header on the TCP stream must
+ * still be consumed.  Without this the next recv() interprets leftover
+ * payload bytes as a PDU header, desynchronises the stream, and tears
+ * down the connection.
+ */
+static void stub_recv_cmd_submit_drain(struct usbip_device *ud,
+				       struct usbip_header *pdu)
+{
+	int bufsz, ret, np;
+	void *buf;
+
+	if (pdu->base.direction == USBIP_DIR_OUT) {
+		bufsz = pdu->u.cmd_submit.transfer_buffer_length;
+		if (bufsz > 0) {
+			buf = kzalloc(min_t(int, bufsz, PAGE_SIZE),
+				      GFP_KERNEL);
+			if (!buf) {
+				usbip_event_add(ud, SDEV_EVENT_ERROR_MALLOC);
+				return;
+			}
+			while (bufsz > 0) {
+				int chunk = min_t(int, bufsz, PAGE_SIZE);
+
+				ret = usbip_recv(ud->tcp_socket, buf, chunk);
+				if (ret != chunk) {
+					kfree(buf);
+					usbip_event_add(ud,
+							SDEV_EVENT_ERROR_TCP);
+					return;
+				}
+				bufsz -= chunk;
+			}
+			kfree(buf);
+		}
+	}
+
+	np = pdu->u.cmd_submit.number_of_packets;
+	if (np > 0 && np <= USBIP_MAX_ISO_PACKETS) {
+		bufsz = np * sizeof(struct usbip_iso_packet_descriptor);
+		buf = kzalloc(bufsz, GFP_KERNEL);
+		if (!buf) {
+			usbip_event_add(ud, SDEV_EVENT_ERROR_MALLOC);
+			return;
+		}
+		ret = usbip_recv(ud->tcp_socket, buf, bufsz);
+		kfree(buf);
+		if (ret != bufsz) {
+			usbip_event_add(ud, SDEV_EVENT_ERROR_TCP);
+			return;
+		}
+	}
+}
+
 static void stub_recv_cmd_submit(struct stub_device *sdev,
 				 struct usbip_header *pdu)
 {
@@ -479,8 +535,10 @@ static void stub_recv_cmd_submit(struct stub_device *sdev,
 	int ret, i;
 	int is_tweaked;
 
-	if (pipe == -1)
+	if (pipe == -1) {
+		stub_recv_cmd_submit_drain(ud, pdu);
 		return;
+	}
 
 	/*
 	 * Smatch reported the error case where use_sg is true and buf_len is 0.
-- 
2.52.0