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>
---
 drivers/usb/serial/io_edgeport.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/serial/io_edgeport.c b/drivers/usb/serial/io_edgeport.c
index 34ccf7820537..503b3b5bb647 100644
--- a/drivers/usb/serial/io_edgeport.c
+++ b/drivers/usb/serial/io_edgeport.c
@@ -646,7 +646,10 @@ 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_t(unsigned int,
+						      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",

base-commit: fad0fd120e29041b3e6cdf41bb12e3184fb524a2
-- 
2.43.0

On Tue, Jul 14, 2026 at 06:34:24PM +0900, Sunho Park wrote:
> 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>
> ---
>  drivers/usb/serial/io_edgeport.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/serial/io_edgeport.c b/drivers/usb/serial/io_edgeport.c
> index 34ccf7820537..503b3b5bb647 100644
> --- a/drivers/usb/serial/io_edgeport.c
> +++ b/drivers/usb/serial/io_edgeport.c
> @@ -646,7 +646,10 @@ 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_t(unsigned int,

LLMs really love to use min_t() as they haven't been trained on modern
kernel code.

Please don't use it, it shouldn't be needed here, right?

thanks,

greg k-h

You're right, I'll use it in v2.

Thanks,
Sunho

2026년 7월 14일 (화) 오후 6:38, Greg Kroah-Hartman <gregkh@linuxfoundation.org>님이 작성:
>
> On Tue, Jul 14, 2026 at 06:34:24PM +0900, Sunho Park wrote:
> > 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>
> > ---
> >  drivers/usb/serial/io_edgeport.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/usb/serial/io_edgeport.c b/drivers/usb/serial/io_edgeport.c
> > index 34ccf7820537..503b3b5bb647 100644
> > --- a/drivers/usb/serial/io_edgeport.c
> > +++ b/drivers/usb/serial/io_edgeport.c
> > @@ -646,7 +646,10 @@ 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_t(unsigned int,
>
> LLMs really love to use min_t() as they haven't been trained on modern
> kernel code.
>
> Please don't use it, it shouldn't be needed here, right?
>
> thanks,
>
> greg k-h