Re: HID: wacom: check for wacom->shared before following the pointer

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



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
--
To unsubscribe from this list: send the line "unsubscribe linux-input" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html




[Index of Archives]     [Linux Media Devel]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Yosemite News]     [Linux Kernel]     [Linux SCSI]     [Linux Wireless Networking]     [Linux Omap]

  Powered by Linux