Hi Kees,
On Wed, Aug 28, 2013 at 10:30 PM, Jiri Kosina <[email protected]> wrote:
> From: Kees Cook <[email protected]>
>
> Many drivers need to validate the characteristics of their HID report
> during initialization to avoid misusing the reports. This adds a common
> helper to perform validation of the report, its field count, and the
> value count within the fields.
>
> Signed-off-by: Kees Cook <[email protected]>
> Cc: [email protected]
> ---
> drivers/hid/hid-core.c | 50
> ++++++++++++++++++++++++++++++++++++++++++++++++
> include/linux/hid.h | 4 ++++
> 2 files changed, 54 insertions(+)
>
> diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
> index 5ea7d51..55798b2 100644
> --- a/drivers/hid/hid-core.c
> +++ b/drivers/hid/hid-core.c
> @@ -759,6 +759,56 @@ int hid_parse_report(struct hid_device *hid, __u8
> *start, unsigned size)
> }
> EXPORT_SYMBOL_GPL(hid_parse_report);
>
> +static const char * const hid_report_names[] = {
> + "HID_INPUT_REPORT",
> + "HID_OUTPUT_REPORT",
> + "HID_FEATURE_REPORT",
> +};
> +/**
> + * hid_validate_report - validate existing device report
> + *
> + * @device: hid device
> + * @type: which report type to examine
> + * @id: which report ID to examine (0 for first)
> + * @fields: expected number of fields
> + * @report_counts: expected number of values per field
> + *
> + * Validate the report details after parsing.
> + */
> +struct hid_report *hid_validate_report(struct hid_device *hid,
> + unsigned int type, unsigned int id,
You should consider having an u8 for id, or at least add a check
against id >= HID_MAX_IDS
> + unsigned int fields,
> + unsigned int report_counts)
> +{
> + struct hid_report *report;
> + unsigned int i;
> +
> + if (type > HID_FEATURE_REPORT) {
> + hid_err(hid, "invalid HID report %u\n", type);
> + return NULL;
> + }
> +
> + report = hid->report_enum[type].report_id_hash[id];
for code readability, and better checking, I'd prefer use
hid_get_report() here instead. Or just add an inlined accessor in
hid.h to retrieve the report from the id as many drivers are using the
report_id_hash directly.
> + if (!report) {
> + hid_err(hid, "missing %s %u\n", hid_report_names[type], id);
> + return NULL;
> + }
> + if (report->maxfield < fields) {
> + hid_err(hid, "not enough fields in %s %u\n",
> + hid_report_names[type], id);
> + return NULL;
> + }
> + for (i = 0; i < fields; i++) {
> + if (report->field[i]->report_count < report_counts) {
This is wrong.
you can have a per field different report_count, and it is perfectly
correct. So the only validate value for report_counts would be 1.
Otherwise, if you want to provide better checking, you need to provide
an array of report_counts, which start beeing a little bit annoying
for users.
> + hid_err(hid, "not enough values in %s %u fields\n",
> + hid_report_names[type], id);
> + return NULL;
> + }
> + }
> + return report;
> +}
> +EXPORT_SYMBOL_GPL(hid_validate_report);
> +
> /**
> * hid_open_report - open a driver-specific device report
> *
> diff --git a/include/linux/hid.h b/include/linux/hid.h
> index ff545cc..76e41d8 100644
> --- a/include/linux/hid.h
> +++ b/include/linux/hid.h
> @@ -749,6 +749,10 @@ void hid_output_report(struct hid_report *report, __u8
> *data);
> struct hid_device *hid_allocate_device(void);
> struct hid_report *hid_register_report(struct hid_device *device, unsigned
> type, unsigned id);
> int hid_parse_report(struct hid_device *hid, __u8 *start, unsigned size);
> +struct hid_report *hid_validate_report(struct hid_device *hid,
> + unsigned int type, unsigned int id,
> + unsigned int fields,
> + unsigned int report_counts);
> int hid_open_report(struct hid_device *device);
> int hid_check_keys_pressed(struct hid_device *hid);
> int hid_connect(struct hid_device *hid, unsigned int connect_mask);
>
> --
> Jiri Kosina
> SUSE Labs
> --
Cheers,
Benjamin
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