[PATCH 6.12.y] USB: serial: cypress_m8: fix memory corruption with small endpoint

[Sasha Levin <sashal@kernel.org>]

From: Johan Hovold <johan@kernel.org>

[ Upstream commit e1a9d791fd66ab2431b9e6f6f835823809869047 ]

Make sure that the interrupt-out endpoint max packet size is at least
eight bytes to avoid user-controlled slab corruption or NULL-pointer
dereference should a malicious device report a smaller size.

Fixes: 3416eaa1f8f8 ("USB: cypress_m8: Packet format is separate from characteristic size")
Cc: stable@vger.kernel.org	# 2.6.26
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/usb/serial/cypress_m8.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/usb/serial/cypress_m8.c b/drivers/usb/serial/cypress_m8.c
index e29569d65991b3..53f27dee35e6bc 100644
--- a/drivers/usb/serial/cypress_m8.c
+++ b/drivers/usb/serial/cypress_m8.c
@@ -445,6 +445,14 @@ static int cypress_generic_port_probe(struct usb_serial_port *port)
 		return -ENODEV;
 	}
 
+	/*
+	 * The buffer must be large enough for the one or two-byte header (and
+	 * following data), but assume anything smaller than eight bytes is
+	 * broken.
+	 */
+	if (port->interrupt_out_size < 8)
+		return -EINVAL;
+
 	priv = kzalloc(sizeof(struct cypress_private), GFP_KERNEL);
 	if (!priv)
 		return -ENOMEM;
-- 
2.53.0