Affected versions of this crate maintains references to memory that might have been freed already.
If affects the following two
tremor-script language constructs:
- A Merge where we assign the result back to the target expression
and the expression to be merged needs to reference the
let state = merge state of event end;
- A Patch where we assign the result back to the target expression
and the patch operations used need to reference the
let state = patch state of insert event.key => event.value end;
For constructs like this (it doesnt matter what is references in the expression to be merged or the patch operations) an optimization
was applied to manipulate the target value in-place, instead of cloning it.
Value struct which underpins all event data in
tremor-script, is representing as borrowed strings
that reference the actual
Vec<u8> the event is based upon. We keep the raw byte-array next to the event structure inside our
Event struct as a self-referential struct,
so we make sure that the structured
Value and its references are valid across its whole lifetime.
The optimization was considered safe as long as it was only possible to merge or patche
event data or static data.
state was introduced to
tremor-script a new possibility existed, to keep
Value data around for longer than the lifetime of an event.
event data is merged or patched into
state without cloning
state first, it can still reference keys or values from
the previous event, which will now be invalid. This allows access to those already freed regions of memory and to get their content out over the wire.
If an upgrade is not possible, a possible workaround is to avoid the optimization
by introducing a temporary variable and not immediately reassigning to
let tmp = merge state of event end;
let state = tmp
The flaw was corrected in
tremor-script version 0.11.6 via commit 1a2efcd by removing the optimization
and always clone the target expression of a Merge or [Patch](https://www.tremor.rs/docs/tremor-script/index#patch.