[PATCH v2] input: touchscreen: wm97xx-core: Fix possible null-pointer dereferences in wm97xx_ts_input_open()

[Jia-Ju Bai <baijiaju1990@gmail.com>]

In wm97xx_ts_input_open(), there is an if statement on line 507 to check
whether wm->mach_ops is NULL:
    if (wm->mach_ops && wm->mach_ops->acc_enabled)

When wm->mach_ops is NULL, it is used on line 521:
    wm97xx_init_pen_irq(wm);
        BUG_ON(!wm->mach_ops->irq_enable);
        BUG_ON(!wm->mach_ops->irq_gpio);
        wm97xx_reg_write(..., reg & ~(wm->mach_ops->irq_gpio))

Thus, possible null-pointer dereferences may occur.

To fix these bugs, wm->mach_ops is checked at the beginning of 
wm97xx_init_pen_irq().

These bugs found by a static analysis tool STCheck written by us.

Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
---
v2:
* Add a new check of wm->mach_ops in wm97xx_init_pen_irq().
  Thank Charles for helpful advice.

---
 drivers/input/touchscreen/wm97xx-core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/input/touchscreen/wm97xx-core.c b/drivers/input/touchscreen/wm97xx-core.c
index 0a174bd82915..50b016abf492 100644
--- a/drivers/input/touchscreen/wm97xx-core.c
+++ b/drivers/input/touchscreen/wm97xx-core.c
@@ -374,6 +374,9 @@ static int wm97xx_init_pen_irq(struct wm97xx *wm)
 {
 	u16 reg;
 
+	if (!wm->mach_ops)
+		return -EINVAL;
+
 	/* If an interrupt is supplied an IRQ enable operation must also be
 	 * provided. */
 	BUG_ON(!wm->mach_ops->irq_enable);
-- 
2.17.0