Re: [PATCH] usb: gadget: serial: Fixed KASAN null-ptr-deref in tty_wakeup

[Greg Kroah-Hartman]

On Wed, Mar 18, 2020 at 10:56:01AM +0800, Li Tao wrote:
> The port->port.tty maybe reset as NULL, If gs_close() was invoked
> unexpectedly during running gserial_connect().
> 
> BUG: KASAN: null-ptr-deref in tty_wakeup+0x1c/0x84
> Call trace:
> [<0000000095c3c837>] dump_backtrace+0x0/0x6d4
> [<0000000047726bb8>] show_stack+0x18/0x20
> [<00000000bedb4c1e>] --dump_stack+0x20/0x28
> [<00000000722f2e2a>] dump_stack+0x84/0xb0
> [<00000000325683d4>] kasan_report_error+0x178/0x1e4
> [<0000000053079998>] kasan_report_error+0x0/0x1e4
> [<00000000b6d33afa>] --asan_load8+0x150/0x15c
> [<00000000188745b8>] tty_wakeup+0x1c/0x84
> [<0000000064f6dd21>] gs_start_io+0xd0/0x11c
> [<0000000063d67b6c>] gserial_connect+0x15c/0x1b0
> [<00000000faf7c0f9>] dm_set_alt+0xa8/0x190
> [<000000008deb1909>] composite_setup+0xde4/0x1edc
> [<00000000792ee16d>] android_setup+0x210/0x294
> [<00000000ab32ef30>] dwc3_ep0_delegate_req+0x48/0x68
> [<0000000054e26fd2>] dwc3_ep0_interrupt+0xf2c/0x16fc
> [<0000000050cb2262>] dwc3_interrupt+0x464/0x1f44
> [<00000000fdcaa6e9>] --handle_irq_event_percpu+0x184/0x398
> [<000000003b24ff56>] handle_irq_event_percpu+0xa0/0x134
> [<00000000aedda5ee>] handle_irq_event+0x60/0xa0
> [<000000005f51a570>] handle_fasteoi_irq+0x23c/0x31c
> [<000000008db2608d>] generic_handle_irq+0x70/0xa4
> [<00000000098683fc>] --handle_domain_irq+0x84/0xe0
> [<000000008ed23b46>] gic_handle_irq+0x98/0xb8
> 
> Signed-off-by: Li Tao <tao.li@xxxxxxxx>
> ---
>  drivers/usb/gadget/function/u_serial.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/gadget/function/u_serial.c b/drivers/usb/gadget/function/u_serial.c
> index 8167d379e115..3c109a8f9ec4 100644
> --- a/drivers/usb/gadget/function/u_serial.c
> +++ b/drivers/usb/gadget/function/u_serial.c
> @@ -565,7 +565,8 @@ static int gs_start_io(struct gs_port *port)
>  		gs_start_tx(port);
>  		/* Unblock any pending writes into our circular buffer, in case
>  		 * we didn't in gs_start_tx() */
> -		tty_wakeup(port->port.tty);
> +		if (port->port.tty)
> +			tty_wakeup(port->port.tty);

What prevents port.tty from being set to NULL between the check and the
call to tty_wakeup?

Shouldn't gs_close() and gserial_connect() have some sort of locking to
prevent this?

thanks,

greg k-h