[PATCH v2 2/3] HID: logitech-hidpp: rework device validation

[Andrey Smirnov]

G920 device only advertises REPORT_ID_HIDPP_LONG and
REPORT_ID_HIDPP_VERY_LONG in its HID report descriptor, so querying
for REPORT_ID_HIDPP_SHORT with optional=false will always fail and
prevent G920 to be recognized as a valid HID++ device.

To fix this and improve some other aspects, modify
hidpp_validate_device() as follows:

  - Inline the code of hidpp_validate_report() to simplify
    distingushing between non-present and invalid report descriptors

  - Drop the check for id >= HID_MAX_IDS || id < 0 since all of our
    IDs are static and known to satisfy that at compile time

  - Change the algorithms to check all possible report
    types (including very long report) and deem the device as a valid
    HID++ device if it supports at least one

  - Treat invalid report length as a hard stop for the validation
    algorithm, meaning that if any of the supported reports has
    invalid length we assume the worst and treat the device as a
    generic HID device.

  - Fold initialization of hidpp->very_long_report_length into
    hidpp_validate_device() since it already fetches very long report
    length and validates its value

Fixes: fe3ee1ec007b ("HID: logitech-hidpp: allow non HID++ devices to be handled by this module")
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=204191
Reported-by: Sam Bazely <sambazley@xxxxxxxxxxxx>
Signed-off-by: Andrey Smirnov <andrew.smirnov@xxxxxxxxx>
Cc: Jiri Kosina <jikos@xxxxxxxxxx>
Cc: Benjamin Tissoires <benjamin.tissoires@xxxxxxxxxx>
Cc: Henrik Rydberg <rydberg@xxxxxxxxxxx>
Cc: Pierre-Loup A. Griffais <pgriffais@xxxxxxxxxxxxxxxxx>
Cc: Austin Palmer <austinp@xxxxxxxxxxxxxxxxx>
Cc: linux-input@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx # 5.2+
---
 drivers/hid/hid-logitech-hidpp.c | 54 ++++++++++++++++++--------------
 1 file changed, 30 insertions(+), 24 deletions(-)

diff --git a/drivers/hid/hid-logitech-hidpp.c b/drivers/hid/hid-logitech-hidpp.c
index 85911586b3b6..8c4be991f387 100644
--- a/drivers/hid/hid-logitech-hidpp.c
+++ b/drivers/hid/hid-logitech-hidpp.c
@@ -3498,34 +3498,45 @@ static int hidpp_get_report_length(struct hid_device *hdev, int id)
 	return report->field[0]->report_count + 1;
 }
 
-static bool hidpp_validate_report(struct hid_device *hdev, int id,
-				  int expected_length, bool optional)
+static bool hidpp_validate_device(struct hid_device *hdev)
 {
-	int report_length;
+	struct hidpp_device *hidpp = hid_get_drvdata(hdev);
+	int id, report_length, supported_reports = 0;
+
+	id = REPORT_ID_HIDPP_SHORT;
+	report_length = hidpp_get_report_length(hdev, id);
+	if (report_length) {
+		if (report_length < HIDPP_REPORT_SHORT_LENGTH)
+			goto bad_device;
 
-	if (id >= HID_MAX_IDS || id < 0) {
-		hid_err(hdev, "invalid HID report id %u\n", id);
-		return false;
+		supported_reports++;
 	}
 
+	id = REPORT_ID_HIDPP_LONG;
 	report_length = hidpp_get_report_length(hdev, id);
-	if (!report_length)
-		return optional;
+	if (report_length) {
+		if (report_length < HIDPP_REPORT_LONG_LENGTH)
+			goto bad_device;
 
-	if (report_length < expected_length) {
-		hid_warn(hdev, "not enough values in hidpp report %d\n", id);
-		return false;
+		supported_reports++;
 	}
 
-	return true;
-}
+	id = REPORT_ID_HIDPP_VERY_LONG;
+	report_length = hidpp_get_report_length(hdev, id);
+	if (report_length) {
+		if (report_length > HIDPP_REPORT_LONG_LENGTH &&
+		    report_length < HIDPP_REPORT_VERY_LONG_MAX_LENGTH)
+			goto bad_device;
 
-static bool hidpp_validate_device(struct hid_device *hdev)
-{
-	return hidpp_validate_report(hdev, REPORT_ID_HIDPP_SHORT,
-				     HIDPP_REPORT_SHORT_LENGTH, false) &&
-	       hidpp_validate_report(hdev, REPORT_ID_HIDPP_LONG,
-				     HIDPP_REPORT_LONG_LENGTH, true);
+		supported_reports++;
+		hidpp->very_long_report_length = report_length;
+	}
+
+	return supported_reports;
+
+bad_device:
+	hid_warn(hdev, "not enough values in hidpp report %d\n", id);
+	return false;
 }
 
 static bool hidpp_application_equals(struct hid_device *hdev,
@@ -3572,11 +3583,6 @@ static int hidpp_probe(struct hid_device *hdev, const struct hid_device_id *id)
 		return hid_hw_start(hdev, HID_CONNECT_DEFAULT);
 	}
 
-	hidpp->very_long_report_length =
-		hidpp_get_report_length(hdev, REPORT_ID_HIDPP_VERY_LONG);
-	if (hidpp->very_long_report_length > HIDPP_REPORT_VERY_LONG_MAX_LENGTH)
-		hidpp->very_long_report_length = HIDPP_REPORT_VERY_LONG_MAX_LENGTH;
-
 	if (id->group == HID_GROUP_LOGITECH_DJ_DEVICE)
 		hidpp->quirks |= HIDPP_QUIRK_UNIFYING;
 
-- 
2.21.0