From 3e19aac2e84a93d1f8ae6e227e0e1ff6e1356594 Mon Sep 17 00:00:00 2001 From: Robert Wing Date: Mon, 18 Dec 2023 15:40:46 -0900 Subject: [PATCH] tty: delete knotes when TTY is revoked Do not clear knotes from the TTY until it gets dealloc'ed, unless the TTY is being revoked, in that case delete the knotes when closed is called on the TTY. When knotes are cleared from a knlist, those knotes become detached from the knlist. And when an event is triggered on a detached knote there isn't an associated knlist and therefore no lock will be taken when the event is triggered. This becomes a problem when a detached knote is triggered on a TTY since the mutex for a TTY is also used as the lock for its knlists. This scenario ends up calling the TTY event handlers without the TTY lock being held and tripping on asserts in the event handlers. PR: 272151 Reviewed by: kib, markj Differential Revision: https://reviews.freebsd.org/D41605 (cherry picked from commit acd5638e268a6706f6b7ad84947a8425e8d51ef7) --- sys/kern/tty.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) diff --git a/sys/kern/tty.c b/sys/kern/tty.c index 8ed59fd166fa2d..42862ffb8a454c 100644 --- a/sys/kern/tty.c +++ b/sys/kern/tty.c @@ -254,9 +254,6 @@ ttydev_leave(struct tty *tp) ttyoutq_free(&tp->t_outq); tp->t_outlow = 0; - knlist_clear(&tp->t_inpoll.si_note, 1); - knlist_clear(&tp->t_outpoll.si_note, 1); - if (!tty_gone(tp)) ttydevsw_close(tp); @@ -370,7 +367,7 @@ done: tp->t_flags &= ~TF_OPENCLOSE; static int ttydev_close(struct cdev *dev, int fflag, int devtype __unused, - struct thread *td __unused) + struct thread *td) { struct tty *tp = dev->si_drv1; @@ -393,8 +390,11 @@ ttydev_close(struct cdev *dev, int fflag, int devtype __unused, } /* If revoking, flush output now to avoid draining it later. */ - if (fflag & FREVOKE) + if ((fflag & FREVOKE) != 0) { tty_flush(tp, FWRITE); + knlist_delete(&tp->t_inpoll.si_note, td, 1); + knlist_delete(&tp->t_outpoll.si_note, td, 1); + } tp->t_flags &= ~TF_EXCLUDE; @@ -1121,6 +1121,8 @@ tty_dealloc(void *arg) ttyoutq_free(&tp->t_outq); seldrain(&tp->t_inpoll); seldrain(&tp->t_outpoll); + knlist_clear(&tp->t_inpoll.si_note, 0); + knlist_clear(&tp->t_outpoll.si_note, 0); knlist_destroy(&tp->t_inpoll.si_note); knlist_destroy(&tp->t_outpoll.si_note);