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.
Thank you Dan and Benjamin.
Ping
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