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authorGreg Kroah-Hartman <gregkh@linuxfoundation.org>2017-04-14 10:57:52 +0200
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2017-04-14 10:59:56 +0200
commita8983d01f9b7d600fbdb3916899edf395954cc83 (patch)
tree59895aefcc519ffa3577379797293c7638837cce
parenta71c9a1c779f2499fb2afc0553e543f18aff6edf (diff)
Revert "tty: don't panic on OOM in tty_set_ldisc()"
This reverts commit 5362544bebe85071188dd9e479b5a5040841c895 as it is reported to cause a reproducable crash. Fixes: 5362544bebe8 ("tty: don't panic on OOM in tty_set_ldisc()") Reported-by: Vegard Nossum <vegard.nossum@gmail.com> Cc: Dmitry Vyukov <dvyukov@google.com> Cc: <syzkaller@googlegroups.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Jiri Slaby <jslaby@suse.com> Cc: Peter Hurley <peter@hurleysoftware.com> Cc: One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk> Cc: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
-rw-r--r--drivers/tty/tty_ldisc.c85
1 files changed, 69 insertions, 16 deletions
diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
index b0500a0a87b8..e4603b09863a 100644
--- a/drivers/tty/tty_ldisc.c
+++ b/drivers/tty/tty_ldisc.c
@@ -492,6 +492,41 @@ static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
}
/**
+ * tty_ldisc_restore - helper for tty ldisc change
+ * @tty: tty to recover
+ * @old: previous ldisc
+ *
+ * Restore the previous line discipline or N_TTY when a line discipline
+ * change fails due to an open error
+ */
+
+static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
+{
+ struct tty_ldisc *new_ldisc;
+ int r;
+
+ /* There is an outstanding reference here so this is safe */
+ old = tty_ldisc_get(tty, old->ops->num);
+ WARN_ON(IS_ERR(old));
+ tty->ldisc = old;
+ tty_set_termios_ldisc(tty, old->ops->num);
+ if (tty_ldisc_open(tty, old) < 0) {
+ tty_ldisc_put(old);
+ /* This driver is always present */
+ new_ldisc = tty_ldisc_get(tty, N_TTY);
+ if (IS_ERR(new_ldisc))
+ panic("n_tty: get");
+ tty->ldisc = new_ldisc;
+ tty_set_termios_ldisc(tty, N_TTY);
+ r = tty_ldisc_open(tty, new_ldisc);
+ if (r < 0)
+ panic("Couldn't open N_TTY ldisc for "
+ "%s --- error %d.",
+ tty_name(tty), r);
+ }
+}
+
+/**
* tty_set_ldisc - set line discipline
* @tty: the terminal to set
* @ldisc: the line discipline
@@ -504,7 +539,12 @@ static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld)
int tty_set_ldisc(struct tty_struct *tty, int disc)
{
- int retval, old_disc;
+ int retval;
+ struct tty_ldisc *old_ldisc, *new_ldisc;
+
+ new_ldisc = tty_ldisc_get(tty, disc);
+ if (IS_ERR(new_ldisc))
+ return PTR_ERR(new_ldisc);
tty_lock(tty);
retval = tty_ldisc_lock(tty, 5 * HZ);
@@ -517,8 +557,7 @@ int tty_set_ldisc(struct tty_struct *tty, int disc)
}
/* Check the no-op case */
- old_disc = tty->ldisc->ops->num;
- if (old_disc == disc)
+ if (tty->ldisc->ops->num == disc)
goto out;
if (test_bit(TTY_HUPPED, &tty->flags)) {
@@ -527,25 +566,34 @@ int tty_set_ldisc(struct tty_struct *tty, int disc)
goto out;
}
- retval = tty_ldisc_reinit(tty, disc);
+ old_ldisc = tty->ldisc;
+
+ /* Shutdown the old discipline. */
+ tty_ldisc_close(tty, old_ldisc);
+
+ /* Now set up the new line discipline. */
+ tty->ldisc = new_ldisc;
+ tty_set_termios_ldisc(tty, disc);
+
+ retval = tty_ldisc_open(tty, new_ldisc);
if (retval < 0) {
/* Back to the old one or N_TTY if we can't */
- if (tty_ldisc_reinit(tty, old_disc) < 0) {
- pr_err("tty: TIOCSETD failed, reinitializing N_TTY\n");
- if (tty_ldisc_reinit(tty, N_TTY) < 0) {
- /* At this point we have tty->ldisc == NULL. */
- pr_err("tty: reinitializing N_TTY failed\n");
- }
- }
+ tty_ldisc_put(new_ldisc);
+ tty_ldisc_restore(tty, old_ldisc);
}
- if (tty->ldisc && tty->ldisc->ops->num != old_disc &&
- tty->ops->set_ldisc) {
+ if (tty->ldisc->ops->num != old_ldisc->ops->num && tty->ops->set_ldisc) {
down_read(&tty->termios_rwsem);
tty->ops->set_ldisc(tty);
up_read(&tty->termios_rwsem);
}
+ /* At this point we hold a reference to the new ldisc and a
+ reference to the old ldisc, or we hold two references to
+ the old ldisc (if it was restored as part of error cleanup
+ above). In either case, releasing a single reference from
+ the old ldisc is correct. */
+ new_ldisc = old_ldisc;
out:
tty_ldisc_unlock(tty);
@@ -553,6 +601,7 @@ out:
already running */
tty_buffer_restart_work(tty->port);
err:
+ tty_ldisc_put(new_ldisc); /* drop the extra reference */
tty_unlock(tty);
return retval;
}
@@ -613,8 +662,10 @@ int tty_ldisc_reinit(struct tty_struct *tty, int disc)
int retval;
ld = tty_ldisc_get(tty, disc);
- if (IS_ERR(ld))
+ if (IS_ERR(ld)) {
+ BUG_ON(disc == N_TTY);
return PTR_ERR(ld);
+ }
if (tty->ldisc) {
tty_ldisc_close(tty, tty->ldisc);
@@ -626,8 +677,10 @@ int tty_ldisc_reinit(struct tty_struct *tty, int disc)
tty_set_termios_ldisc(tty, disc);
retval = tty_ldisc_open(tty, tty->ldisc);
if (retval) {
- tty_ldisc_put(tty->ldisc);
- tty->ldisc = NULL;
+ if (!WARN_ON(disc == N_TTY)) {
+ tty_ldisc_put(tty->ldisc);
+ tty->ldisc = NULL;
+ }
}
return retval;
}