The patch titled Subject: tty: fall back to N_NULL if switching to N_TTY fails during hangup has been removed from the -mm tree. Its filename was tty-fall-back-to-n_null-if-switching-to-n_tty-fails-during-hangup.patch This patch was dropped because it was merged into mainline or a subsystem tree ------------------------------------------------------ From: Johannes Weiner <hannes@xxxxxxxxxxx> Subject: 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 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@xxxxxxxxxxx Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Alan Cox <alan@llwyncelyn.cymru> Cc: Christoph Hellwig <hch@xxxxxx> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- drivers/tty/tty_ldisc.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) diff -puN drivers/tty/tty_ldisc.c~tty-fall-back-to-n_null-if-switching-to-n_tty-fails-during-hangup drivers/tty/tty_ldisc.c --- a/drivers/tty/tty_ldisc.c~tty-fall-back-to-n_null-if-switching-to-n_tty-fails-during-hangup +++ a/drivers/tty/tty_ldisc.c @@ -694,10 +694,8 @@ int tty_ldisc_reinit(struct tty_struct * 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 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); } _ Patches currently in -mm which might be from hannes@xxxxxxxxxxx are -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html