On Mon, Feb 13, 2023 at 05:06:10PM +0530, Prashanth K wrote:
> Consider a case where gserial_disconnect has already cleared
> gser->ioport. And if a wakeup interrupt triggers afterwards,
> gserial_resume gets called, which will lead to accessing of
> gser->ioport and thus causing null pointer dereference.Add
> a null pointer check to prevent this.
>
> Added a static spinlock to prevent gser->ioport from becoming
> null after the newly added check.
>
> Fixes: aba3a8d01d62 ("usb: gadget: u_serial: add suspend resume callbacks")
> Signed-off-by: Prashanth K <quic_prashk@xxxxxxxxxxx>
> ---
> v4: Added short comment about serial_port_lock.
>
> drivers/usb/gadget/function/u_serial.c | 27 +++++++++++++++++++++++----
> 1 file changed, 23 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/usb/gadget/function/u_serial.c b/drivers/usb/gadget/function/u_serial.c
> index 840626e..3a6adf2 100644
> --- a/drivers/usb/gadget/function/u_serial.c
> +++ b/drivers/usb/gadget/function/u_serial.c
> @@ -82,6 +82,13 @@
> #define WRITE_BUF_SIZE 8192 /* TX only */
> #define GS_CONSOLE_BUF_SIZE 8192
>
> +/*
> + * Since all the spinlocks used in this driver is part of struct gs_port (port_lock).
> + * Added a new static spinlock to prevent race conditions where gs_port is dereferenced
> + * after marking as null.
> + */
This comment could be a little shorter and more direct. Something like:
/* Prevents race conditions when accessing gser->ioport */
or
/* Prevents races between disconnect and resume for gser->ioport */
or even just
/* Protects gser->ioport */
Everything else looks okay.
Alan Stern
> +static DEFINE_SPINLOCK(serial_port_lock);
> +
> /* console info */
> struct gs_console {
> struct console console;
> @@ -1375,8 +1382,10 @@ void gserial_disconnect(struct gserial *gser)
> if (!port)
> return;
>
> + spin_lock_irqsave(&serial_port_lock, flags);
> +
> /* tell the TTY glue not to do I/O here any more */
> - spin_lock_irqsave(&port->port_lock, flags);
> + spin_lock(&port->port_lock);
>
> gs_console_disconnect(port);
>
> @@ -1391,7 +1400,8 @@ void gserial_disconnect(struct gserial *gser)
> tty_hangup(port->port.tty);
> }
> port->suspended = false;
> - spin_unlock_irqrestore(&port->port_lock, flags);
> + spin_unlock(&port->port_lock);
> + spin_unlock_irqrestore(&serial_port_lock, flags);
>
> /* disable endpoints, aborting down any active I/O */
> usb_ep_disable(gser->out);
> @@ -1425,10 +1435,19 @@ EXPORT_SYMBOL_GPL(gserial_suspend);
>
> void gserial_resume(struct gserial *gser)
> {
> - struct gs_port *port = gser->ioport;
> + struct gs_port *port;
> unsigned long flags;
>
> - spin_lock_irqsave(&port->port_lock, flags);
> + spin_lock_irqsave(&serial_port_lock, flags);
> + port = gser->ioport;
> +
> + if (!port) {
> + spin_unlock_irqrestore(&serial_port_lock, flags);
> + return;
> + }
> +
> + spin_lock(&port->port_lock);
> + spin_unlock(&serial_port_lock);
> port->suspended = false;
> if (!port->start_delayed) {
> spin_unlock_irqrestore(&port->port_lock, flags);
> --
> 2.7.4
>
