n_gsm: gsm_data_alloc buffer allocation could fail and it is not being checked

gsm_data_alloc buffer allocation could fail and it is not being checked.

Add check for allocated buffer and return if the buffer allocation
fails.

Signed-off-by: Ken Mills <ken.k.mills@intel.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Cc: stable@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/tty/n_gsm.c

@@ -968,6 +968,8 @@ static void gsm_control_reply(struct gsm_mux *gsm, int cmd, u8 *data,
 {
 	struct gsm_msg *msg;
 	msg = gsm_data_alloc(gsm, 0, dlen + 2, gsm->ftype);
+	if (msg == NULL)
+		return;
 	msg->data[0] = (cmd & 0xFE) << 1 | EA;	/* Clear C/R */
 	msg->data[1] = (dlen << 1) | EA;
 	memcpy(msg->data + 2, data, dlen);