Messages in this thread | | | Date | Thu, 22 Apr 2021 12:02:31 +0200 | From | Greg Kroah-Hartman <> | Subject | Re: [PATCH] ttyprintk: Add TTY hangup callback. |
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On Sun, Apr 18, 2021 at 01:16:05PM +0200, Samo Pogačnik wrote: > 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 <syzbot+43e93968b964e369db0b@syzkaller.appspotmail.com> > > Reported-by: syzbot <syzbot+3ed715090790806d8b18@syzkaller.appspotmail.com> > > Tested-by: syzbot <syzbot+43e93968b964e369db0b@syzkaller.appspotmail.com> > > Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> > > 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.
Thanks for the review, I'll go queue this up.
greg k-h
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