Merge #19109: Only allow getdata of recently announced invs

f32c408f3a0b7e597977df2bc2cdc4ae298586e5 Make sure unconfirmed parents are requestable (Pieter Wuille)
c4626bcd211af08c85b6567ef07eeae333edba47 Drop setInventoryTxToSend based filtering (Pieter Wuille)
43f02ccbff9b137d59458da7a8afdb0bf80e127f Only respond to requests for recently announced transactions (Pieter Wuille)
b24a17f03982c9cd8fd6ec665b16e022374c96f0 Introduce constant for mempool-based relay separate from mapRelay caching (Pieter Wuille)
a9bc5638031a29abaa40284273a3507b345c31e9 Swap relay pool and mempool lookup (Pieter Wuille)

Pull request description:

  This implements the follow-up suggested here: https://github.com/bitcoin/bitcoin/pull/18861#issuecomment-627630111 . Instead of checking `setInventoryTxToSend`, maintain an explicit bloom filter with the 3500 most recently announced invs, and permit fetching any of these as long as they're in the relay pool or the mempool. In addition, permit relay from the mempool after just 2 minutes instead of 15.

  This:

  * Fixes the brief opportunity an attacker has to request unannounced invs just after the connection is established (pointed out by naumenkogs, see https://github.com/bitcoin/bitcoin/pull/18861#issuecomment-627627010).
  * Guarantees that locally resubmitted invs after `filterInventoryKnown` rolls over can still be requested (pointed out by luke-jr, see https://github.com/bitcoin/bitcoin/pull/18861#discussion_r419695831).

  It adds 37 KiB of filter per peer.

  This is also a step towards dropping the relay pool entirely and always relaying from the mempool directly (see #17303), but that is still blocked by dealing properly with NOTFOUNDs (see #18238).

ACKs for top commit:
  jnewbery:
    reACK f32c408f3
  jonatack:
    re-ACK f32c408 per `git range-diff f7c19e8 2da7ee3 f32c408` and redid the following: code review, thought about motivation, DoS and privacy aspects, debug build to check for warnings after updating Clang from 6 to 11 since last review.
  ajtowns:
    re-ACK f32c408f3a0b7e597977df2bc2cdc4ae298586e5

Tree-SHA512: aa05b9fd01bad59581c4ec91836a52d7415dc933fa49d4c4adced79aa25aaad51e11166357e8c8b29fbf6021a7401b98c21b850b5d8e8ad773fdb5d6608e1e85

0 files changed, 0 insertions, 0 deletions