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    Subject[PATCH 4.4 16/44] tty: Dont call panic() at tty_ldisc_init()
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>

    commit 903f9db10f18f735e62ba447147b6c434b6af003 upstream.

    syzbot is reporting kernel panic [1] triggered by memory allocation failure
    at tty_ldisc_get() from tty_ldisc_init(). But since both tty_ldisc_get()
    and caller of tty_ldisc_init() can cleanly handle errors, tty_ldisc_init()
    does not need to call panic() when tty_ldisc_get() failed.

    [1] https://syzkaller.appspot.com/bug?id=883431818e036ae6a9981156a64b821110f39187

    Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
    Reported-by: syzbot <syzkaller@googlegroups.com>
    Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Cc: Jiri Slaby <jslaby@suse.com>
    Cc: stable <stable@vger.kernel.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/tty/tty_io.c | 5 ++++-
    drivers/tty/tty_ldisc.c | 5 +++--
    include/linux/tty.h | 2 +-
    3 files changed, 8 insertions(+), 4 deletions(-)

    --- a/drivers/tty/tty_io.c
    +++ b/drivers/tty/tty_io.c
    @@ -3154,7 +3154,10 @@ struct tty_struct *alloc_tty_struct(stru

    kref_init(&tty->kref);
    tty->magic = TTY_MAGIC;
    - tty_ldisc_init(tty);
    + if (tty_ldisc_init(tty)) {
    + kfree(tty);
    + return NULL;
    + }
    tty->session = NULL;
    tty->pgrp = NULL;
    mutex_init(&tty->legacy_mutex);
    --- a/drivers/tty/tty_ldisc.c
    +++ b/drivers/tty/tty_ldisc.c
    @@ -804,12 +804,13 @@ void tty_ldisc_release(struct tty_struct
    * the tty structure is not completely set up when this call is made.
    */

    -void tty_ldisc_init(struct tty_struct *tty)
    +int tty_ldisc_init(struct tty_struct *tty)
    {
    struct tty_ldisc *ld = tty_ldisc_get(tty, N_TTY);
    if (IS_ERR(ld))
    - panic("n_tty: init_tty");
    + return PTR_ERR(ld);
    tty->ldisc = ld;
    + return 0;
    }

    /**
    --- a/include/linux/tty.h
    +++ b/include/linux/tty.h
    @@ -586,7 +586,7 @@ extern int tty_unregister_ldisc(int disc
    extern int tty_set_ldisc(struct tty_struct *tty, int ldisc);
    extern int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty);
    extern void tty_ldisc_release(struct tty_struct *tty);
    -extern void tty_ldisc_init(struct tty_struct *tty);
    +extern int __must_check tty_ldisc_init(struct tty_struct *tty);
    extern void tty_ldisc_deinit(struct tty_struct *tty);
    extern void tty_ldisc_begin(void);


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