USB: serial: io_edgeport: cap received transmit credits

The interrupt-status packet reports transmit credits returned by the
device. edge_interrupt_callback() adds the 16-bit value to txCredits
without checking maxTxCredits.

edge_write() uses txCredits minus the software FIFO count as the amount
of data that fits. Since the FIFO is allocated with maxTxCredits bytes,
txCredits exceeding maxTxCredits can cause OOB write in ring buffer.

Cap accumulated credits at maxTxCredits. Conforming devices should never
hit the cap.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Assisted-by: Codex:GPT-5
Signed-off-by: Sunho Park <shpark061104@gmail.com>
Signed-off-by: Johan Hovold <johan@kernel.org>

diff --git a/drivers/usb/serial/io_edgeport.c b/drivers/usb/serial/io_edgeport.c
index 34ccf78205371a81f52c3a085fb7cf9af7dc0790..eaa8f00716c87da14aa972e617d6b0b4a90317d2 100644 (file)
--- a/drivers/usb/serial/io_edgeport.c
+++ b/drivers/usb/serial/io_edgeport.c
@@ -646,7 +646,8 @@ static void edge_interrupt_callback(struct urb *urb)
                                if (edge_port && edge_port->open) {
                                        spin_lock_irqsave(&edge_port->ep_lock,
                                                          flags);
-                                       edge_port->txCredits += txCredits;
+                                       edge_port->txCredits = min(edge_port->txCredits + txCredits,
+                                                                  edge_port->maxTxCredits);
                                        spin_unlock_irqrestore(&edge_port->ep_lock,
                                                               flags);
                                        dev_dbg(dev, "%s - txcredits for port%d = %d\n",