From f4cf7a384587c16c59565dd6930dd763f243dba4 Mon Sep 17 00:00:00 2001 From: Peter Hurley Date: Mon, 11 Mar 2013 16:44:29 -0400 Subject: [PATCH] tty: Halt both ldiscs concurrently The pty driver does not obtain an ldisc reference to the linked tty when writing. When the ldiscs are sequentially halted, it is possible for one ldisc to be halted, and before the second ldisc can be halted, a concurrent write schedules buffer work on the first ldisc. This can lead to an access-after-free error when the scheduled buffer work starts on the closed ldisc. Prevent subsequent use after halt by performing each stage of the halt on both ttys. Signed-off-by: Peter Hurley Signed-off-by: Greg Kroah-Hartman --- drivers/tty/tty_ldisc.c | 38 +++++++++++++++++++++++++------------- 1 file changed, 25 insertions(+), 13 deletions(-) diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c index 525ee535c10d..77120911e016 100644 --- a/drivers/tty/tty_ldisc.c +++ b/drivers/tty/tty_ldisc.c @@ -530,14 +530,17 @@ static int tty_ldisc_wait_idle(struct tty_struct *tty, long timeout) /** * tty_ldisc_halt - shut down the line discipline * @tty: tty device + * @o_tty: paired pty device (can be NULL) * @pending: returns true if work was scheduled when cancelled * (can be set to NULL) + * @o_pending: returns true if work was scheduled when cancelled + * (can be set to NULL) * @timeout: # of jiffies to wait for ldisc refs to be released * - * Shut down the line discipline and work queue for this tty device. - * The TTY_LDISC flag being cleared ensures no further references can - * be obtained while the delayed work queue halt ensures that no more - * data is fed to the ldisc. + * Shut down the line discipline and work queue for this tty device and + * its paired pty (if exists). Clearing the TTY_LDISC flag ensures + * no further references can be obtained while the work queue halt + * ensures that no more data is fed to the ldisc. * * Furthermore, guarantee that existing ldisc references have been * released, which in turn, guarantees that no future buffer work @@ -548,19 +551,32 @@ static int tty_ldisc_wait_idle(struct tty_struct *tty, long timeout) * flushed. */ -static int tty_ldisc_halt(struct tty_struct *tty, int *pending, long timeout) +static int tty_ldisc_halt(struct tty_struct *tty, struct tty_struct *o_tty, + int *pending, int *o_pending, long timeout) { - int scheduled, retval; + int scheduled, o_scheduled, retval; clear_bit(TTY_LDISC, &tty->flags); + if (o_tty) + clear_bit(TTY_LDISC, &o_tty->flags); + retval = tty_ldisc_wait_idle(tty, timeout); + if (!retval && o_tty) + retval = tty_ldisc_wait_idle(o_tty, timeout); if (retval) return retval; scheduled = cancel_work_sync(&tty->port->buf.work); set_bit(TTY_LDISC_HALTED, &tty->flags); + if (o_tty) { + o_scheduled = cancel_work_sync(&o_tty->port->buf.work); + set_bit(TTY_LDISC_HALTED, &o_tty->flags); + } + if (pending) *pending = scheduled; + if (o_tty && o_pending) + *o_pending = o_scheduled; return 0; } @@ -702,9 +718,7 @@ int tty_set_ldisc(struct tty_struct *tty, int ldisc) * parallel to the change and re-referencing the tty. */ - retval = tty_ldisc_halt(tty, &work, 5 * HZ); - if (!retval && o_tty) - retval = tty_ldisc_halt(o_tty, &o_work, 5 * HZ); + retval = tty_ldisc_halt(tty, o_tty, &work, &o_work, 5 * HZ); /* * Wait for ->hangup_work and ->buf.work handlers to terminate. @@ -965,12 +979,10 @@ void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty) * race with the set_ldisc code path. */ - tty_ldisc_halt(tty, NULL, MAX_SCHEDULE_TIMEOUT); + tty_ldisc_halt(tty, o_tty, NULL, NULL, MAX_SCHEDULE_TIMEOUT); tty_ldisc_flush_works(tty); - if (o_tty) { - tty_ldisc_halt(o_tty, NULL, MAX_SCHEDULE_TIMEOUT); + if (o_tty) tty_ldisc_flush_works(o_tty); - } tty_lock_pair(tty, o_tty); /* This will need doing differently if we need to lock */ -- 2.30.2