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...
Thanks for the report and the analysis!
Cheers,
Benjamin
>
> 1105 int slot = input_mt_get_slot_by_key(input,
> data[offset + 1]);
> 1106
> 1107 if (slot < 0)
> 1108 continue;
>
> regards,
> dan carpenter
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