Dne 15.04.2021 (čet) ob 09:22 +0900 je Tetsuo Handa napisal(a):
> syzbot is reporting hung task due to flood of
>
> tty_warn(tty, "%s: tty->count = 1 port count = %d\n", __func__,
> port->count);
>
> message [1], for ioctl(TIOCVHANGUP) prevents tty_port_close() from
> decrementing port->count due to tty_hung_up_p() == true.
>
> ----------
> #include <sys/types.h>
> #include <sys/stat.h>
> #include <fcntl.h>
> #include <sys/ioctl.h>
> #include <unistd.h>
>
> int main(int argc, char *argv[])
> {
> int i;
> int fd[10];
>
> for (i = 0; i < 10; i++)
> fd[i] = open("/dev/ttyprintk", O_WRONLY);
> ioctl(fd[0], TIOCVHANGUP);
> for (i = 0; i < 10; i++)
> close(fd[i]);
> close(open("/dev/ttyprintk", O_WRONLY));
> return 0;
> }
> ----------
>
> When TTY hangup happens, port->count needs to be reset via
> "struct tty_operations"->hangup callback.
>
> [1]
> https://syzkaller.appspot.com/bug?id=39ea6caa479af471183997376dc7e90bc7d64a6a
>
> Reported-by: syzbot <[email protected]>
> Reported-by: syzbot <[email protected]>
> Tested-by: syzbot <[email protected]>
> Signed-off-by: Tetsuo Handa <[email protected]>
> Fixes: 24b4b67d17c308aa ("add ttyprintk driver")
> ---
> drivers/char/ttyprintk.c | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/drivers/char/ttyprintk.c b/drivers/char/ttyprintk.c
> index 6a0059e508e3..93f5d11c830b 100644
> --- a/drivers/char/ttyprintk.c
> +++ b/drivers/char/ttyprintk.c
> @@ -158,12 +158,23 @@ static int tpk_ioctl(struct tty_struct *tty,
> return 0;
> }
>
> +/*
> + * TTY operations hangup function.
> + */
> +static void tpk_hangup(struct tty_struct *tty)
> +{
> + struct ttyprintk_port *tpkp = tty->driver_data;
> +
> + tty_port_hangup(&tpkp->port);
> +}
> +
> static const struct tty_operations ttyprintk_ops = {
> .open = tpk_open,
> .close = tpk_close,
> .write = tpk_write,
> .write_room = tpk_write_room,
> .ioctl = tpk_ioctl,
> + .hangup = tpk_hangup,
> };
>
> static const struct tty_port_operations null_ops = { };
Using the supplied test code, i've tested the patch on my desktop running the
5.4 kernel. After applying the patch, the kernel warnings like "ttyprintk:
tty_port_close_start: tty->count = 1 port count = 11" do not appear any more,
when the test code is run.
I think the patch is ok.
best regards, Samo
