| Message ID | 1676117858-32157-1-git-send-email-quic_prashk@quicinc.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [v2] usb: gadget: u_serial: Add null pointer check in gserial_resume | expand |
On Sat, Feb 11, 2023 at 05:47:38PM +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@quicinc.com> > --- > v2: Added static spinlock and fixed Fixes tag. > > drivers/usb/gadget/function/u_serial.c | 16 ++++++++++++++-- > 1 file changed, 14 insertions(+), 2 deletions(-) > > diff --git a/drivers/usb/gadget/function/u_serial.c b/drivers/usb/gadget/function/u_serial.c > index 840626e..9ced0fa 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); > + > /* console info */ > struct gs_console { > struct console console; > @@ -1370,11 +1372,13 @@ EXPORT_SYMBOL_GPL(gserial_connect); > void gserial_disconnect(struct gserial *gser) > { > struct gs_port *port = gser->ioport; > - unsigned long flags; > + unsigned long flags, serial_flag; You don't need two separate flags here. The fact that you wrote this indicates you don't understand how spin_lock_irqsave() and spin_lock_irqrestore() work. When spin_lock_irqsave(&lock, flag) is called, it saves the current INT (interrupt-enable) setting in flag, disables interrupts, and acquires the lock. When spin_unlock_irqrestore(&lock, flag) is called, it releases the lock and writes the value in flag back to the INT setting. The end result is that if interrupts were enabled before spin_lock_irqsave() then they will be enabled after spin_unlock_irqrestore(). If interrupts were disabled beforehand, they will remain disabled afterward. And either way, interrupts will be disabled between the two calls. > > if (!port) > return; > > + spin_lock_irqsave(&serial_port_lock, serial_flag); So now interrupts are disabled. > + > /* tell the TTY glue not to do I/O here any more */ > spin_lock_irqsave(&port->port_lock, flags); Hence there's no need for flag here. You don't need to save the current INT setting because you already know what it is: interrupts are disabled. You can simply call spin_lock(), which will acquire the lock without doing anything to the INT setting. > > @@ -1392,6 +1396,7 @@ void gserial_disconnect(struct gserial *gser) > } > port->suspended = false; > spin_unlock_irqrestore(&port->port_lock, flags); Likewise, here you can call spin_unlock(). > + spin_unlock_irqrestore(&serial_port_lock, serial_flag); > > /* 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; > - unsigned long flags; > + unsigned long flags, serial_flag; > + > + spin_lock_irqsave(&serial_port_lock, serial_flag); > + if (!port) { > + spin_unlock_irqrestore(&serial_port_lock, serial_flag); > + return; > + } This is a little trickier, but the same principles apply. Since spin_lock_irqsave() was called above, interrupts are now disabled. > > spin_lock_irqsave(&port->port_lock, flags); So there's no need for _irqsave here. > + spin_unlock_irqrestore(&serial_port_lock, serial_flag); And here you must not use spin_unlock_irqrestore(). This will do the wrong thing, because it will enable interrupts if they were enabled at the start of the function. Then you would be running with port->port_lock held and interrupts enabled, a bad combination. > port->suspended = false; > if (!port->start_delayed) { > spin_unlock_irqrestore(&port->port_lock, flags); Here, at the final unlock, is where you should restore the INT setting to the value it had at the start of the function. Alan Stern
diff --git a/drivers/usb/gadget/function/u_serial.c b/drivers/usb/gadget/function/u_serial.c index 840626e..9ced0fa 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); + /* console info */ struct gs_console { struct console console; @@ -1370,11 +1372,13 @@ EXPORT_SYMBOL_GPL(gserial_connect); void gserial_disconnect(struct gserial *gser) { struct gs_port *port = gser->ioport; - unsigned long flags; + unsigned long flags, serial_flag; if (!port) return; + spin_lock_irqsave(&serial_port_lock, serial_flag); + /* tell the TTY glue not to do I/O here any more */ spin_lock_irqsave(&port->port_lock, flags); @@ -1392,6 +1396,7 @@ void gserial_disconnect(struct gserial *gser) } port->suspended = false; spin_unlock_irqrestore(&port->port_lock, flags); + spin_unlock_irqrestore(&serial_port_lock, serial_flag); /* 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; - unsigned long flags; + unsigned long flags, serial_flag; + + spin_lock_irqsave(&serial_port_lock, serial_flag); + if (!port) { + spin_unlock_irqrestore(&serial_port_lock, serial_flag); + return; + } spin_lock_irqsave(&port->port_lock, flags); + spin_unlock_irqrestore(&serial_port_lock, serial_flag); port->suspended = false; if (!port->start_delayed) { spin_unlock_irqrestore(&port->port_lock, flags);
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@quicinc.com> --- v2: Added static spinlock and fixed Fixes tag. drivers/usb/gadget/function/u_serial.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-)