git: acd5638e268a - main - tty: delete knotes when TTY is revoked

The branch main has been updated by rew:

URL: https://cgit.FreeBSD.org/src/commit/?id=acd5638e268a6706f6b7ad84947a8425e8d51ef7

commit acd5638e268a6706f6b7ad84947a8425e8d51ef7
Author:     Robert Wing <rew@FreeBSD.org>
AuthorDate: 2023-12-19 00:40:46 +0000
Commit:     Robert Wing <rew@FreeBSD.org>
CommitDate: 2023-12-19 00:40:46 +0000

    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
---
 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 e051c66ab0c9..61a6beafa2c0 100644
--- a/sys/kern/tty.c
+++ b/sys/kern/tty.c
@@ -253,9 +253,6 @@ 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);
 
@@ -369,7 +366,7 @@ 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;
 
@@ -392,8 +389,11 @@ 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;
 
@@ -1120,6 +1120,8 @@ 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);