[PATCH 1/4] tty: n_gsm: add some locking around gsm_mux[]

[Dan Carpenter]

We should take "gsm_mux_lock" when we access gsm_mux[].

Reported-by: Sun Peng <sun_p...@topsec.com.cn>
Signed-off-by: Dan Carpenter <dan.carpen...@oracle.com>

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 3b3e1f6632d7..cc7f68814200 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2898,18 +2898,22 @@ static int gsmtty_install(struct tty_driver *driver, 
struct tty_struct *tty)
        bool alloc = false;
        int ret;
 
-       line = line & 0x3F;
 
        if (mux >= MAX_MUX)
                return -ENXIO;
-       /* FIXME: we need to lock gsm_mux for lifetimes of ttys eventually */
-       if (gsm_mux[mux] == NULL)
-               return -EUNATCH;
+
+       line = line & 0x3F;
        if (line == 0 || line > 61)     /* 62/63 reserved */
                return -ECHRNG;
+
+       spin_lock(&gsm_mux_lock);
        gsm = gsm_mux[mux];
+       spin_unlock(&gsm_mux_lock);
+       if (!gsm)
+               return -EUNATCH;
        if (gsm->dead)
                return -EL2HLT;
+
        /* If DLCI 0 is not yet fully open return an error.
        This is ok from a locking
        perspective as we don't have to worry about this