Jiri: On Sat, 23 Nov 2019, Andrey Konovalov wrote: > I'm not sure, but the stack trace reminds me of this issue, so this > report might be related: > > https://groups.google.com/d/msg/syzkaller-bugs/X0zVbh8aFEM/NsPcshjxBgAJ No, the issue is quite different, although it is also a bug in the HID parser. The big problem is that the parser assumes all usages will belong to a collection. There's also a second, smaller bug: hid_apply_multipler() assumes every Resolution Multiplier control is associated with a Logical Collection (i.e., there's no way the routine can ever set multiplier_collection to NULL) even though there's a big quotation from the HID Usage Table manual at the start of the function saying that they don't have to be. This bug can be fixed easily, though. The first bug is more troublesome. hid_add_usage() explicitly sets the parser->local.collection_index[] entry to 0 if the current collection stack is empty. But there's no way to distinguish this 0 from a genuine index value that happens to point to the first collection! So what should happen when a usage appears outside of all collections? Is it a bug in the report descriptor (the current code suggests that it is not)? Or should we use a different sentinel value for the collection_index[] entry, one that cannot be confused with a genuine value, such as UINT_MAX? Awaiting your suggestion... Alan Stern
