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authorJohannes Weiner <hannes@cmpxchg.org>2017-10-13 15:58:08 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2017-10-13 16:18:33 -0700
commite65c62b1375cbff69fa925787bcdae4b27bffb48 (patch)
treec1669f5d423d29b4fff75f9c36bc49217a114ee9
parentb8c8a338f75e052d9fa2fed851259320af412e3f (diff)
downloadlinux-sh-e65c62b1375cbff69fa925787bcdae4b27bffb48.tar.gz
tty: fall back to N_NULL if switching to N_TTY fails during hangup
We have seen NULL-pointer dereference crashes in tty->disc_data when the N_TTY fallback driver failed to open during hangup. The immediate cause of this open to fail has been addressed in the preceding patch to vmalloc(), but this code could be more robust. As Alan pointed out in commit 8a8dabf2dd68 ("tty: handle the case where we cannot restore a line discipline"), the N_TTY driver, historically the safe fallback that could never fail, can indeed fail, but the surrounding code is not prepared to handle this. To avoid crashes he added a new N_NULL driver to take N_TTY's place as the last resort. Hook that fallback up to the hangup path. Update tty_ldisc_reinit() to reflect the reality that n_tty_open can indeed fail. Link: http://lkml.kernel.org/r/20171004185959.GC2136@cmpxchg.org Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> Cc: Alan Cox <alan@llwyncelyn.cymru> Cc: Christoph Hellwig <hch@lst.de> Cc: Dmitry Vyukov <dvyukov@google.com> Cc: Michal Hocko <mhocko@suse.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--drivers/tty/tty_ldisc.c11
1 files changed, 5 insertions, 6 deletions
diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c
index 2fe216b276e2..84a8ac2a779f 100644
--- a/drivers/tty/tty_ldisc.c
+++ b/drivers/tty/tty_ldisc.c
@@ -694,10 +694,8 @@ 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) {
- if (!WARN_ON(disc == N_TTY)) {
- tty_ldisc_put(tty->ldisc);
- tty->ldisc = NULL;
- }
+ tty_ldisc_put(tty->ldisc);
+ tty->ldisc = NULL;
}
return retval;
}
@@ -752,8 +750,9 @@ void tty_ldisc_hangup(struct tty_struct *tty, bool reinit)
if (tty->ldisc) {
if (reinit) {
- if (tty_ldisc_reinit(tty, tty->termios.c_line) < 0)
- tty_ldisc_reinit(tty, N_TTY);
+ if (tty_ldisc_reinit(tty, tty->termios.c_line) < 0 &&
+ tty_ldisc_reinit(tty, N_TTY) < 0)
+ WARN_ON(tty_ldisc_reinit(tty, N_NULL) < 0);
} else
tty_ldisc_kill(tty);
}