On Wed, Dec 21, 2022 at 05:32:48PM +0100, Krzysztof Kozlowski wrote:
> use-after-free is visible in serdev-ttyport, e.g. during system reboot
> with Qualcomm Atheros Bluetooth. The TTY is closed, thus "struct
> tty_struct" is being released, but the hci_uart_qca driver performs
> writes and flushes during system shutdown in qca_serdev_shutdown().
>
> Unable to handle kernel paging request at virtual address 0072662f67726fd7
> ...
> CPU: 6 PID: 1 Comm: systemd-shutdow Tainted: G W 6.1.0-rt5-00325-g8a5f56bcfcca #8
> Hardware name: Qualcomm Technologies, Inc. Robotics RB5 (DT)
> Call trace:
> tty_driver_flush_buffer+0x4/0x30
> serdev_device_write_flush+0x24/0x34
> qca_serdev_shutdown+0x80/0x130 [hci_uart]
> device_shutdown+0x15c/0x260
> kernel_restart+0x48/0xac
>
> KASAN report:
>
> BUG: KASAN: use-after-free in tty_driver_flush_buffer+0x1c/0x50
> Read of size 8 at addr ffff16270c2e0018 by task systemd-shutdow/1
>
> CPU: 7 PID: 1 Comm: systemd-shutdow Not tainted 6.1.0-next-20221220-00014-gb85aaf97fb01-dirty #28
> Hardware name: Qualcomm Technologies, Inc. Robotics RB5 (DT)
> Call trace:
> dump_backtrace.part.0+0xdc/0xf0
> show_stack+0x18/0x30
> dump_stack_lvl+0x68/0x84
> print_report+0x188/0x488
> kasan_report+0xa4/0xf0
> __asan_load8+0x80/0xac
> tty_driver_flush_buffer+0x1c/0x50
> ttyport_write_flush+0x34/0x44
> serdev_device_write_flush+0x48/0x60
> qca_serdev_shutdown+0x124/0x274
> device_shutdown+0x1e8/0x350
> kernel_restart+0x48/0xb0
> __do_sys_reboot+0x244/0x2d0
> __arm64_sys_reboot+0x54/0x70
> invoke_syscall+0x60/0x190
> el0_svc_common.constprop.0+0x7c/0x160
> do_el0_svc+0x44/0xf0
> el0_svc+0x2c/0x6c
> el0t_64_sync_handler+0xbc/0x140
> el0t_64_sync+0x190/0x194
>
> Fixes: bed35c6dfa6a ("serdev: add a tty port controller driver")
> Cc: <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>
> ---
> drivers/tty/serdev/serdev-ttyport.c | 24 ++++++++++++++++++++++++
> 1 file changed, 24 insertions(+)
>
> diff --git a/drivers/tty/serdev/serdev-ttyport.c b/drivers/tty/serdev/serdev-ttyport.c
> index d367803e2044..3d2bab91a988 100644
> --- a/drivers/tty/serdev/serdev-ttyport.c
> +++ b/drivers/tty/serdev/serdev-ttyport.c
> @@ -91,6 +91,9 @@ static void ttyport_write_flush(struct serdev_controller *ctrl)
> struct serport *serport = serdev_controller_get_drvdata(ctrl);
> struct tty_struct *tty = serport->tty;
>
> + if (!test_bit(SERPORT_ACTIVE, &serport->flags))
> + return;
Shouldn't that be a more useful macro/function instead?
serport_is_active(serport)
Anyway, what prevents this from changing _right_ after you test it and
before you call the next line in this function (same for all invocations
here.)
thanks,
greg k-h
