[PATCH 5.4 116/158] speakup: Do not let the line discipline be used several times

Greg Kroah-Hartman
2020-11-23T12:39:33Z

From: Samuel Thibault <samuel.thibault@ens-lyon.org>

commit d4122754442799187d5d537a9c039a49a67e57f1 upstream.

Speakup has only one speakup_tty variable to store the tty it is managing. This
makes sense since its codebase currently assumes that there is only one user who
controls the screen reading.

That however means that we have to forbid using the line discipline several
times, otherwise the second closure would try to free a NULL ldisc_data, leading to

general protection fault: 0000 [#1] SMP KASAN PTI
RIP: 0010:spk_ttyio_ldisc_close+0x2c/0x60
Call Trace:
tty_ldisc_release+0xa2/0x340
tty_release_struct+0x17/0xd0
tty_release+0x9d9/0xcc0
__fput+0x231/0x740
task_work_run+0x12c/0x1a0
do_exit+0x9b5/0x2230
? release_task+0x1240/0x1240
? __do_page_fault+0x562/0xa30
do_group_exit+0xd5/0x2a0
__x64_sys_exit_group+0x35/0x40
do_syscall_64+0x89/0x2b0
? page_fault+0x8/0x30
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Cc: stable@vger.kernel.org
Reported-by: 秦世松 <qinshisong1205@gmail.com>
Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Tested-by: Shisong Qin <qinshisong1205@gmail.com>
Link: https://lore.kernel.org/r/20201110183541.fzgnlwhjpgqzjeth@function
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/staging/speakup/spk_ttyio.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)

--- a/drivers/staging/speakup/spk_ttyio.c
+++ b/drivers/staging/speakup/spk_ttyio.c
@@ -49,15 +49,25 @@ static int spk_ttyio_ldisc_open(struct t

if (!tty->ops->write)
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)
+ if (!ldisc_data) {
+ speakup_tty = NULL;
+ mutex_unlock(&speakup_tty_mutex);
return -ENOMEM;
+ }

init_completion(&ldisc_data->completion);
ldisc_data->buf_free = true;
speakup_tty->disc_data = ldisc_data;
+ mutex_unlock(&speakup_tty_mutex);

return 0;
}