linux-kernel - [PATCH v2] HID: fix error message in hid_open

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Message-Id: <5866b49b330a750b44003ebd9f532541dcb13f18.1566587656.git.mirq-linux@rere.qmqm.pl>
Date:   Fri, 23 Aug 2019 21:15:27 +0200
From:   Michał Mirosław <mirq-linux@...e.qmqm.pl>
To:     linux-input@...r.kernel.org
Cc:     Jiri Kosina <jikos@...nel.org>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2] HID: fix error message in hid_open_report()

On HID report descriptor parsing error the code displays bogus
pointer instead of error offset (subtracts start=NULL from end).
Make the message more useful by displaying correct error offset
and include total buffer size for reference.

This was carried over from ancient times - "Fixed" commit just
promoted the message from DEBUG to ERROR.

Cc: stable@...r.kernel.org
Fixes: 8c3d52fc393b ("HID: make parser more verbose about parsing errors by default")
Signed-off-by: Michał Mirosław <mirq-linux@...e.qmqm.pl>

---
v2: fixed printf() warning spotted by Jiri Kosina <jikos@...nel.org>

 * against v5.2.9

Signed-off-by: Michał Mirosław <mirq-linux@...e.qmqm.pl>
---
 drivers/hid/hid-core.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
index 210b81a56e1a..3af76624e4aa 100644
--- a/drivers/hid/hid-core.c
+++ b/drivers/hid/hid-core.c
@@ -1139,6 +1139,7 @@ int hid_open_report(struct hid_device *device)
 	__u8 *start;
 	__u8 *buf;
 	__u8 *end;
+	__u8 *next;
 	int ret;
 	static int (*dispatch_type[])(struct hid_parser *parser,
 				      struct hid_item *item) = {
@@ -1192,7 +1193,8 @@ int hid_open_report(struct hid_device *device)
 	device->collection_size = HID_DEFAULT_NUM_COLLECTIONS;
 
 	ret = -EINVAL;
-	while ((start = fetch_item(start, end, &item)) != NULL) {
+	while ((next = fetch_item(start, end, &item)) != NULL) {
+		start = next;
 
 		if (item.format != HID_ITEM_FORMAT_SHORT) {
 			hid_err(device, "unexpected long global item\n");
@@ -1230,7 +1232,8 @@ int hid_open_report(struct hid_device *device)
 		}
 	}
 
-	hid_err(device, "item fetching failed at offset %d\n", (int)(end - start));
+	hid_err(device, "item fetching failed at offset %u/%u\n",
+		size - (unsigned int)(end - start), size);
 err:
 	kfree(parser->collection_stack);
 alloc_err:
-- 
2.20.1