From: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> Date: 2020-03-18 18:12:40 To: Li Tao <tao.li@xxxxxxxx> Cc: Felipe Balbi <balbi@xxxxxxxxxx>,"Michał Mirosław" <mirq-linux@xxxxxxxxxxxx>,Sergey Organov <sorganov@xxxxxxxxx>,linux-usb@xxxxxxxxxxxxxxx,linux-kernel@xxxxxxxxxxxxxxx,wenhu.wang@xxxxxxxx Subject: Re: [PATCH] usb: gadget: serial: Fixed KASAN null-ptr-deref in tty_wakeup>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? > I encountered this issue on Samsung EXYNOS980 platform, Maybe this is platform specific issue. The USB interrupt handler got port_lock on CPU 0 in gserial_connect while gs_close is waiting for this lock on CPU 1. But this port_lock will unlock in gs_start_io-->gs_start_rx temporarily, This race condition may cause port.tty set as NULL. greg k-h, Do you have some good suggestions? >thanks, > >greg k-h
