On Sun, Feb 12, 2023 at 01:37:13AM +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>
> ---
This looks pretty good, except for a couple of small things...
> v3: Fixed the spin_lock_irqsave flags.
>
> drivers/usb/gadget/function/u_serial.c | 22 +++++++++++++++++-----
> 1 file changed, 17 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/usb/gadget/function/u_serial.c b/drivers/usb/gadget/function/u_serial.c
> index 840626e..471087f 100644
> --- a/drivers/usb/gadget/function/u_serial.c
> +++ b/drivers/usb/gadget/function/u_serial.c
> @@ -82,6 +82,8 @@
> #define WRITE_BUF_SIZE 8192 /* TX only */
> #define GS_CONSOLE_BUF_SIZE 8192
>
> +static DEFINE_SPINLOCK(serial_port_lock);
You might put a short comment before this line, explaining what the
purpose of serial_port_lock is. Otherwise people will wonder what it is
for.
> +
> /* console info */
> struct gs_console {
> struct console console;
> @@ -1370,13 +1372,15 @@ EXPORT_SYMBOL_GPL(gserial_connect);
> void gserial_disconnect(struct gserial *gser)
> {
> struct gs_port *port = gser->ioport;
> - unsigned long flags;
> + unsigned long flags;
Unnecessary whitespace change. Leave the original code as it is.
>
> if (!port)
> return;
Is it really possible for port to be NULL here? If it is possible,
where would gser->ioport be set to NULL?
And if it's not possible, this test should be removed.
>
> + 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 +1395,8 @@ 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);
> @@ -1426,9 +1431,16 @@ EXPORT_SYMBOL_GPL(gserial_suspend);
> void gserial_resume(struct gserial *gser)
> {
> struct gs_port *port = gser->ioport;
You shouldn't read gser->ioport here; do it under the protection of the
static spinlock. If you do the read here then there will still be a
data race, because gserial_disconnect() might change the value just as
you are reading it.
> - unsigned long flags;
> + unsigned long flags;
Again, unnecessary whitespace change.
>
> - spin_lock_irqsave(&port->port_lock, flags);
> + spin_lock_irqsave(&serial_port_lock, flags);
Here is where you should read 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);
Alan Stern
