usb: gadget: u_serial: Add null pointer check in gserial_resume

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")
Cc: stable <stable@kernel.org>
Signed-off-by: Prashanth K <quic_prashk@quicinc.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Link: https://lore.kernel.org/r/1676309438-14922-1-git-send-email-quic_prashk@quicinc.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/gadget/function/u_serial.c b/drivers/usb/gadget/function/u_serial.c
index 840626e..a0ca47f 100644 (file)
--- a/drivers/usb/gadget/function/u_serial.c
+++ b/drivers/usb/gadget/function/u_serial.c
@@ -82,6 +82,9 @@
 #define WRITE_BUF_SIZE         8192            /* TX only */
 #define GS_CONSOLE_BUF_SIZE    8192
 
+/* Prevents race conditions while accessing gser->ioport */
+static DEFINE_SPINLOCK(serial_port_lock);
+
 /* console info */
 struct gs_console {
        struct console          console;
@@ -1375,8 +1378,10 @@ 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 +1396,8 @@ 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 +1431,19 @@ 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);