From: Samuel Thibault <samuel.thibault@xxxxxxxxxxxx> commit f0992098cadb4c9c6a00703b66cafe604e178fea upstream. Speakup exposing a line discipline allows userland to try to use it, while it is deemed to be useless, and thus uselessly exposes potential bugs. One of them is simply that in such a case if the line sends data, spk_ttyio_receive_buf2 is called and crashes since spk_ttyio_synth is NULL. This change restricts the use of the speakup line discipline to speakup drivers, thus avoiding such kind of issues altogether. Cc: stable@xxxxxxxxxxxxxxx Reported-by: Shisong Qin <qinshisong1205@xxxxxxxxx> Signed-off-by: Samuel Thibault <samuel.thibault@xxxxxxxxxxxx> Tested-by: Shisong Qin <qinshisong1205@xxxxxxxxx> Link: https://lore.kernel.org/r/20201129193523.hm3f6n5xrn6fiyyc@function Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/staging/speakup/spk_ttyio.c | 38 +++++++++++++++++++++--------------- 1 file changed, 23 insertions(+), 15 deletions(-) --- a/drivers/staging/speakup/spk_ttyio.c +++ b/drivers/staging/speakup/spk_ttyio.c @@ -46,28 +46,20 @@ static int spk_ttyio_ldisc_open(struct t { struct spk_ldisc_data *ldisc_data; + if (tty != speakup_tty) + /* Somebody tried to use this line discipline outside speakup */ + return -ENODEV; + if (tty->ops->write == NULL) return -EOPNOTSUPP; - mutex_lock(&speakup_tty_mutex); - if (speakup_tty) { - mutex_unlock(&speakup_tty_mutex); - return -EBUSY; - } - speakup_tty = tty; - ldisc_data = kmalloc(sizeof(struct spk_ldisc_data), GFP_KERNEL); - if (!ldisc_data) { - speakup_tty = NULL; - mutex_unlock(&speakup_tty_mutex); - pr_err("speakup: Failed to allocate ldisc_data.\n"); + if (!ldisc_data) return -ENOMEM; - } sema_init(&ldisc_data->sem, 0); ldisc_data->buf_free = true; - speakup_tty->disc_data = ldisc_data; - mutex_unlock(&speakup_tty_mutex); + tty->disc_data = ldisc_data; return 0; } @@ -184,9 +176,25 @@ static int spk_ttyio_initialise_ldisc(st tty_unlock(tty); + mutex_lock(&speakup_tty_mutex); + speakup_tty = tty; ret = tty_set_ldisc(tty, N_SPEAKUP); if (ret) - pr_err("speakup: Failed to set N_SPEAKUP on tty\n"); + speakup_tty = NULL; + mutex_unlock(&speakup_tty_mutex); + + if (!ret) + /* Success */ + return 0; + + pr_err("speakup: Failed to set N_SPEAKUP on tty\n"); + + tty_lock(tty); + if (tty->ops->close) + tty->ops->close(tty, NULL); + tty_unlock(tty); + + tty_kclose(tty); return ret; }
