| Message ID | 20220217080555.5387-4-daniel.starke@siemens.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [1/1] tty: n_gsm: fix NULL pointer access due to DLCI release | expand |
diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c index 0b1808e3a912..e63154ef0b6c 100644 --- a/drivers/tty/n_gsm.c +++ b/drivers/tty/n_gsm.c @@ -1748,7 +1748,12 @@ static void gsm_dlci_release(struct gsm_dlci *dlci) gsm_destroy_network(dlci); mutex_unlock(&dlci->mutex); - tty_hangup(tty); + /* We cannot use tty_hangup() because in tty_kref_put() the tty + * driver assumes that the hangup queue is free and reuses it to + * queue release_one_tty() -> NULL pointer panic in + * process_one_work(). + */ + tty_vhangup(tty); tty_port_tty_set(&dlci->port, NULL); tty_kref_put(tty);
The here fixed commit made the tty hangup asynchronous to avoid a circular locking warning. I could not reproduce this warning. Furthermore, due to the asynchronous hangup the function call now gets queued up while the underlying tty is being freed. Depending on the timing this results in a NULL pointer access in the global work queue scheduler. To be precise in process_one_work(). Therefore, the previous commit made the issue worse which it tried to fix. This patch fixes this by falling back to the old behavior which uses a blocking tty hangup call before freeing up the associated tty. Fixes: 7030082a7415 ("tty: n_gsm: avoid recursive locking with async port hangup") Cc: stable@vger.kernel.org Signed-off-by: Daniel Starke <daniel.starke@siemens.com> --- drivers/tty/n_gsm.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)