Re: [PATCH] nfc: pn533: initialize struct pn533_out_arg properly

[Simon Horman]

On Tue, Mar 07, 2023 at 12:48:38AM +0300, Fedor Pchelkin wrote:
> struct pn533_out_arg used as a temporary context for out_urb is not
> initialized properly. Its uninitialized 'phy' field can be dereferenced in
> error cases inside pn533_out_complete() callback function. It causes the
> following failure:
> 
> general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN
> KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
> CPU: 1 PID: 0 Comm: swapper/1 Not tainted 6.2.0-rc3-next-20230110-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
> RIP: 0010:pn533_out_complete.cold+0x15/0x44 drivers/nfc/pn533/usb.c:441
> Call Trace:
>  <IRQ>
>  __usb_hcd_giveback_urb+0x2b6/0x5c0 drivers/usb/core/hcd.c:1671
>  usb_hcd_giveback_urb+0x384/0x430 drivers/usb/core/hcd.c:1754
>  dummy_timer+0x1203/0x32d0 drivers/usb/gadget/udc/dummy_hcd.c:1988
>  call_timer_fn+0x1da/0x800 kernel/time/timer.c:1700
>  expire_timers+0x234/0x330 kernel/time/timer.c:1751
>  __run_timers kernel/time/timer.c:2022 [inline]
>  __run_timers kernel/time/timer.c:1995 [inline]
>  run_timer_softirq+0x326/0x910 kernel/time/timer.c:2035
>  __do_softirq+0x1fb/0xaf6 kernel/softirq.c:571
>  invoke_softirq kernel/softirq.c:445 [inline]
>  __irq_exit_rcu+0x123/0x180 kernel/softirq.c:650
>  irq_exit_rcu+0x9/0x20 kernel/softirq.c:662
>  sysvec_apic_timer_interrupt+0x97/0xc0 arch/x86/kernel/apic/apic.c:1107
> 
> Initialize the field with the pn533_usb_phy currently used.
> 
> Fixes: 9dab880d675b ("nfc: pn533: Wait for out_urb's completion in pn533_usb_send_frame()")
> Reported-by: syzbot+1e608ba4217c96d1952f@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Fedor Pchelkin <pchelkin@xxxxxxxxx>
> ---
>  drivers/nfc/pn533/usb.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/nfc/pn533/usb.c b/drivers/nfc/pn533/usb.c
> index ed9c5e2cf3ad..159b331b3bf6 100644
> --- a/drivers/nfc/pn533/usb.c
> +++ b/drivers/nfc/pn533/usb.c
> @@ -162,7 +162,7 @@ static int pn533_usb_send_frame(struct pn533 *dev,
>  				struct sk_buff *out)
>  {
>  	struct pn533_usb_phy *phy = dev->phy;
> -	struct pn533_out_arg arg;
> +	struct pn533_out_arg arg = {.phy = phy};

nit: This doesn't follow reverse xmas tree ordering - longest to shortest line.
     It's probably not worth respinning, but I expect the preferred
     approach is (*completely untested!*)

	...
	struct pn533_out_arg arg;
	...

	arg.phy = phy;

>  	void *cntx;
>  	int rc;
>  
> -- 
> 2.34.1
>