wire: Clear tx inputs/outputs before deserialize.#3621
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The code that handles deserializing transaction scripts by way of the free list cleans up in the event of error by returning the non-nil scripts to the free list to avoid leaking them. This is making an implicit (and undocumented) assumption that it is only deserializing into empty instances and therefore any non-nil scripts in the inputs and outputs in the event of a failed deserialization came from the free list. The consequence of that is that it is possible that any slices that were set by the caller prior to a failed deserialization could incorrectly be returned to the free list and ultimately get clobbered later. While this is not an issue for dcrd since it never deserializes into non-empty instances, there is no guarantee that is true for all callers. In order to ensure safety for all callers, this nils the input and output slices prior to deserializing anything in order to ensure the aforementioned assumption is always satisfied.
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The code that handles deserializing transaction scripts by way of the free list cleans up in the event of error by returning the non-nil scripts to the free list to avoid leaking them.
This is making an implicit (and undocumented) assumption that it is only deserializing into empty instances and therefore any non-nil scripts in the inputs and outputs in the event of a failed deserialization came from the free list. The consequence of that is that it is possible that any slices that were set by the caller prior to a failed deserialization could incorrectly be returned to the free list and ultimately get clobbered later.
While this is not an issue for dcrd since it never deserializes into non-empty instances, there is no guarantee that is true for all callers.
In order to ensure safety for all callers, this nils the input and output slices prior to deserializing anything in order to ensure the aforementioned assumption is always satisfied.