[PATCH] tty: n_gsm: add missing tty_kref_put

[Pavel Skripkin <paskripkin@gmail.com>]

My local syzbot instance hit memory leak in gsmld_attach_gsm(). The
reproducer injects allocation failure in tty_register_device(). After
this error only previous tty_register_device() calls unwinded, but not
tty_kref_get().

It leads to tty_struct leak, because ->close() won't be called in case
of ->open() failure and nothing puts tty reference.

Fixes: 0a360e8b65d6 ("tty: n_gsm: check error while registering tty devices")
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
---
 drivers/tty/n_gsm.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 1d92d2a84889..1cc3aec17d2d 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2394,6 +2394,8 @@ static int gsmld_attach_gsm(struct tty_struct *tty, struct gsm_mux *gsm)
 				for (i--; i >= 1; i--)
 					tty_unregister_device(gsm_tty_driver,
 								base + i);
+
+				tty_kref_put(gsm->tty);
 				return PTR_ERR(dev);
 			}
 		}
-- 
2.33.1