[PATCH 5.10 55/57] HID: core: fix number/pointer type confusion on long items

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

5.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jann Horn <jannh@google.com>

commit 28abce951343fcec26e397610868efa4e1395c3f upstream.

When fetch_item() is called by hid_scan_report() on an item with
HID_ITEM_TAG_LONG, it stores a pointer to the item data in
item->data.longdata instead of storing a value directly in
item->data.{u8/u16/u32}.

When item_udata() or item_sdata() encounters such an item, it incorrectly
assumes that the item is in short format, and therefore returns the lower
part of a kernel pointer reinterpreted as a number.

When a HID device is connected whose descriptor contains a
HID_GLOBAL_ITEM_TAG_REPORT_SIZE encoded in long format with size=4, this
causes the lower half of a kernel pointer to be printed into dmesg as a
number, like this:

    hid (null): invalid report_size 107953555

To fix it, let item_udata() and item_sdata() verify that the item is in
short format.

Note that this bug only affects hid_scan_report(), while the main parsing
pass hid_parse_collections() will always bail out when encountering a long
item.

Sidenote: There are currently no users of data.longdata; maybe we should
just remove any parsing of long-format descriptors as a follow-up.

Fixes: 3dc8fc083dbf ("HID: Use hid_parser for pre-scanning the report descriptors")
Cc: stable@vger.kernel.org
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/hid/hid-core.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/drivers/hid/hid-core.c
+++ b/drivers/hid/hid-core.c
@@ -346,6 +346,9 @@ static int hid_add_field(struct hid_pars
 
 static u32 item_udata(struct hid_item *item)
 {
+	if (item->format != HID_ITEM_FORMAT_SHORT)
+		return 0;
+
 	switch (item->size) {
 	case 1: return item->data.u8;
 	case 2: return item->data.u16;
@@ -356,6 +359,9 @@ static u32 item_udata(struct hid_item *i
 
 static s32 item_sdata(struct hid_item *item)
 {
+	if (item->format != HID_ITEM_FORMAT_SHORT)
+		return 0;
+
 	switch (item->size) {
 	case 1: return item->data.s8;
 	case 2: return item->data.s16;