On Mar 19 2015 or thereabouts, Ping Cheng wrote:
> On Thu, Mar 19, 2015 at 9:06 AM, Benjamin Tissoires
> <benjamin.tissoires@xxxxxxxxxx> wrote:
> > Hi Dan,
> >
> > On Mar 19 2015 or thereabouts, Dan Carpenter wrote:
> >> Hello Benjamin Tissoires,
> >>
> >> This is a semi-automatic email about new static checker warnings.
> >>
> >> The patch e2c7d8877e5c: "HID: wacom: check for wacom->shared before
> >> following the pointer" from Mar 5, 2015, leads to the following
> >> Smatch complaint:
> >>
> >> drivers/hid/wacom_wac.c:602 wacom_intuos_inout()
> >> error: we previously assumed 'wacom->shared' could be null (see line 584)
> >>
> >> drivers/hid/wacom_wac.c
> >> 583
> >> 584 if (wacom->shared) {
> >>
> >> In the original code we checked "if (features->quirks & WACOM_QUIRK_MULTI_INPUT)"
> >> which is ensures that "wacom->shared" is non-NULL.
> >>
> >> 585 wacom->shared->stylus_in_proximity = true;
> >> 586
> >> 587 if (wacom->shared->touch_down)
> >> 588 return 1;
> >> 589 }
> >> 590
> >> 591 /* in Range while exiting */
> >> 592 if (((data[1] & 0xfe) == 0x20) && wacom->reporting_data) {
> >> 593 input_report_key(input, BTN_TOUCH, 0);
> >> 594 input_report_abs(input, ABS_PRESSURE, 0);
> >> 595 input_report_abs(input, ABS_DISTANCE, wacom->features.distance_max);
> >> 596 return 2;
> >> 597 }
> >> 598
> >> 599 /* Exit report */
> >> 600 if ((data[1] & 0xfe) == 0x80) {
> >> 601 if (features->quirks & WACOM_QUIRK_MULTI_INPUT)
> >> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> >> We still check for that here. Smatch is confused.
> >>
> >> 602 wacom->shared->stylus_in_proximity = false;
> >> ^^^^^^^^^^^^^
> >> This is not a bug, but change the previous change to
> >> "if (wacom->shared)" would make the code more consistent.
> >
> > Yep, I agree. That's for these cases that I preferred having a test
> > against wacom->shared not null rather than (features->quirks &
> > WACOM_QUIRK_MULTI_INPUT).
> >
> >>
> >> 603 wacom->reporting_data = false;
> >> 604
> >>
> >> [ snip ]
> >>
> >> 1072 static int wacom_24hdt_irq(struct wacom_wac *wacom)
> >> 1073 {
> >> 1074 struct input_dev *input = wacom->input;
> >> 1075 unsigned char *data = wacom->data;
> >> 1076 int i;
> >> 1077 int current_num_contacts = data[61];
> >> 1078 int contacts_to_send = 0;
> >> 1079 int num_contacts_left = 4; /* maximum contacts per packet */
> >> 1080 int byte_per_packet = WACOM_BYTES_PER_24HDT_PACKET;
> >> 1081 int y_offset = 2;
> >> 1082 static int contact_with_no_pen_down_count = 0;
> >> 1083
> >> 1084 if (wacom->features.type == WACOM_27QHDT) {
> >> 1085 current_num_contacts = data[63];
> >> 1086 num_contacts_left = 10;
> >> 1087 byte_per_packet = WACOM_BYTES_PER_QHDTHID_PACKET;
> >> 1088 y_offset = 0;
> >> 1089 }
> >> 1090
> >> 1091 /*
> >> 1092 * First packet resets the counter since only the first
> >> 1093 * packet in series will have non-zero current_num_contacts.
> >> 1094 */
> >> 1095 if (current_num_contacts) {
> >> 1096 wacom->num_contacts_left = current_num_contacts;
> >> 1097 contact_with_no_pen_down_count = 0;
> >> 1098 }
> >> 1099
> >> 1100 contacts_to_send = min(num_contacts_left, wacom->num_contacts_left);
> >> 1101
> >> 1102 for (i = 0; i < contacts_to_send; i++) {
> >> 1103 int offset = (byte_per_packet * i) + 1;
> >> 1104 bool touch = (data[offset] & 0x1) && !wacom->shared->stylus_in_proximity;
> >> ^^^^^^^^^^^^^
> >> I assume this hardware is always quirky so this won't cause a NULL
> >> deref?
> >
> > Yes. 24hdt has the quirk WACOM_QUIRK_MULTI_INPUT, so wacom->shared can
> > not be null. I wonder what we could put in the code to make static
> > checkers happy...
>
> I am working on a solution. Patches will be submitted soon.
>
Thanks Ping. That lower me my workload and is very appreciated.
> Thank you Dan and Benjamin.
Thanks dan for your answer (not in this thread, but heh...)
Cheers,
Benjamin
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