HID: wacom: Have wacom_tpc_irq guard against possible NULL dereference

The following Smatch complaint was generated in response to commit
2a6cdbd ("HID: wacom: Introduce new 'touch_input' device"):

    drivers/hid/wacom_wac.c:1586 wacom_tpc_irq()
             error: we previously assumed 'wacom->touch_input' could be null (see line 1577)

The 'touch_input' and 'pen_input' variables point to the 'struct input_dev'
used for relaying touch and pen events to userspace, respectively. If a
device does not have a touch interface or pen interface, the associated
input variable is NULL. The 'wacom_tpc_irq()' function is responsible for
forwarding input reports to a more-specific IRQ handler function. An
unknown report could theoretically be mistaken as e.g. a touch report
on a device which does not have a touch interface. This can be prevented
by only calling the pen/touch functions are called when the pen/touch
pointers are valid.

Fixes: 2a6cdbd ("HID: wacom: Introduce new 'touch_input' device")
Signed-off-by: Jason Gerecke <jason.gerecke@wacom.com>
Reviewed-by: Ping Cheng <ping.cheng@wacom.com>
Cc: stable@vger.kernel.org
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

diff --git a/drivers/hid/wacom_wac.c b/drivers/hid/wacom_wac.c
index 4b225fb19a16842f635026d1b1023d5d1cf5068e..e274c9dc32f3a211d97d02f2b6477f20c9121fac 100644 (file)
--- a/drivers/hid/wacom_wac.c
+++ b/drivers/hid/wacom_wac.c
@@ -1571,37 +1571,38 @@ static int wacom_tpc_irq(struct wacom_wac *wacom, size_t len)
 {
        unsigned char *data = wacom->data;
 
-       if (wacom->pen_input)
+       if (wacom->pen_input) {
                dev_dbg(wacom->pen_input->dev.parent,
                        "%s: received report #%d\n", __func__, data[0]);
-       else if (wacom->touch_input)
+
+               if (len == WACOM_PKGLEN_PENABLED ||
+                   data[0] == WACOM_REPORT_PENABLED)
+                       return wacom_tpc_pen(wacom);
+       }
+       else if (wacom->touch_input) {
                dev_dbg(wacom->touch_input->dev.parent,
                        "%s: received report #%d\n", __func__, data[0]);
 
-       switch (len) {
-       case WACOM_PKGLEN_TPC1FG:
-               return wacom_tpc_single_touch(wacom, len);
+               switch (len) {
+               case WACOM_PKGLEN_TPC1FG:
+                       return wacom_tpc_single_touch(wacom, len);
 
-       case WACOM_PKGLEN_TPC2FG:
-               return wacom_tpc_mt_touch(wacom);
+               case WACOM_PKGLEN_TPC2FG:
+                       return wacom_tpc_mt_touch(wacom);
 
-       case WACOM_PKGLEN_PENABLED:
-               return wacom_tpc_pen(wacom);
+               default:
+                       switch (data[0]) {
+                       case WACOM_REPORT_TPC1FG:
+                       case WACOM_REPORT_TPCHID:
+                       case WACOM_REPORT_TPCST:
+                       case WACOM_REPORT_TPC1FGE:
+                               return wacom_tpc_single_touch(wacom, len);
 
-       default:
-               switch (data[0]) {
-               case WACOM_REPORT_TPC1FG:
-               case WACOM_REPORT_TPCHID:
-               case WACOM_REPORT_TPCST:
-               case WACOM_REPORT_TPC1FGE:
-                       return wacom_tpc_single_touch(wacom, len);
-
-               case WACOM_REPORT_TPCMT:
-               case WACOM_REPORT_TPCMT2:
-                       return wacom_mt_touch(wacom);
+                       case WACOM_REPORT_TPCMT:
+                       case WACOM_REPORT_TPCMT2:
+                               return wacom_mt_touch(wacom);
 
-               case WACOM_REPORT_PENABLED:
-                       return wacom_tpc_pen(wacom);
+                       }
                }
        }