In order to prevent memory DoS, we must ensure that we don't accept a new
header into memory until we've performed anti-DoS checks, such as verifying
that the header is part of a sufficiently high work chain. This commit adds a
new argument to AcceptBlockHeader() so that we can ensure that all call-sites
which might cause a new header to be accepted into memory have to grapple with
the question of whether the header is safe to accept, or needs further
validation.
This patch also fixes two places where low-difficulty-headers could have been
processed without such validation (processing an unrequested block from the
network, and processing a compact block).
Credit to Niklas Gögge for noticing this issue, and thanks to Sjors Provoost
for test code.
c4c5b9ca6e consensus/params: set default values for BIP9Deployment (Anthony Towns)
Pull request description:
Adds default values for `vDeployments` in `consensus/params.h` so that undefined behaviour is avoided if a deployment is not initialized. Also adds a check in the unit tests to alert if this is happening, since even if it doesn't invoke undefined behaviour it's probably a mistake.
ACKs for top commit:
laanwj:
Code review ACK c4c5b9ca6e
Tree-SHA512: 22d7ff86a817d9e9e67c47301fc3b7e9d5821c13565d7706711f113dea220eea29b413a7c8d029691009159cebc85a108d77cb52418734091c196bafb2b12423
Add sanity asserts for return value of `CBlockIndex::GetAncestor()` where appropriate.
In validation.cpp `CheckSequenceLocks`, check the return value of `tip->GetAncestor(maxInputHeight)` stored into `lp->maxInputBlock`. If it ever returns `nullptr` because the ancestor isn't found, it's going to be a bad bug to keep going, since a `LockPoints` object with the `maxInputBlock` member set to `nullptr` signifies no relative lock time.
In the other places, the added asserts would prevent accidental dereferencing of a null pointer which is undefined behavior.
Co-Authored-By: Aurèle Oulès <aurele@oules.com>
Co-Authored-By: danra <danra@users.noreply.github.com>
While chainparams should explicilty set values for each possible
entry in vDeployments, in the past that has been missed resulting
in potential undefined behaviour due to accessing unitinitialized
data. Reduce the severity of future bugs of that nature by providing
benign default values. Adds a unit test to alert if the default value
is not overwritten for the real chains (NEVER_ACTIVE/NEVER_ACTIVE rather
than NEVER_ACTIVE/NO_TIMEOUT).
cccc1e70b8 Enforce Taproot script flags whenever WITNESS is set (MarcoFalke)
fa42299411 Remove nullptr check in GetBlockScriptFlags (MarcoFalke)
faadc606c7 refactor: Pass const reference instead of pointer to GetBlockScriptFlags (MarcoFalke)
Pull request description:
Now that Taproot is active, it makes sense to enforce its rules on all blocks, even historic ones, regardless of the deployment status.
### Benefits:
(With "script flags" I mean "taproot script verification flags".)
* Script flags are known ahead for all blocks (even blocks not yet created) and do not change. This may benefit static analysis, code review, and development of new script features that build on Taproot.
* Any future bugs introduced in the deployment code won't have any effect on the script flags, as they are independent of deployment.
* Enforcing the taproot rules regardless of the deployment status makes testing easier because invalid blocks after activation are also invalid before activation. So there is no need to differentiate the two cases.
* It gives belt-and-suspenders protection against a practically expensive and theoretically impossible IBD reorg attack where the node is eclipsed. While `nMinimumChainWork` already protects against this, the cost for a few months worth of POW might be lowered until a major version release of Bitcoin Core reaches EOL. The needed work for the attack is the difference between `nMinimumChainWork` and the work at block 709632.
For reference, previously the same was done for P2SH and WITNESS in commit 0a8b7b4b33.
### Implementation:
I found one block which fails verification with the flags applied, so I added a `TaprootException`, similar to the `BIP16Exception`.
For reference, the debug log:
```
ERROR: ConnectBlock(): CheckInputScripts on b10c007c60e14f9d087e0291d4d0c7869697c6681d979c6639dbd960792b4d41 failed with non-mandatory-script-verify-flag (Witness program was passed an empty witness)
BlockChecked: block hash=0000000000000000000f14c35b2d841e986ab5441de8c585d5ffe55ea1e395ad state=non-mandatory-script-verify-flag (Witness program was passed an empty witness)
InvalidChainFound: invalid block=0000000000000000000f14c35b2d841e986ab5441de8c585d5ffe55ea1e395ad height=692261 log2_work=92.988459 date=2021-07-23T08:24:20Z
InvalidChainFound: current best=0000000000000000000067b17a4c0ffd77c29941b15ad356ca8f980af137a25d height=692260 log2_work=92.988450 date=2021-07-23T07:47:31Z
ERROR: ConnectTip: ConnectBlock 0000000000000000000f14c35b2d841e986ab5441de8c585d5ffe55ea1e395ad failed, non-mandatory-script-verify-flag (Witness program was passed an empty witness)
```
Hint for testing, make sure to set `-noassumevalid`.
### Considerations
Obviously this change can lead to consensus splits on the network in light of massive reorgs. Currently the last block before Taproot activation, that is the last block without the Taproot script flags set, is only buried by a few days of POW. However, when and if this patch is included in the next major release, it will be buried by a few months of POW. BIP90 considerations apply when looking at reorgs this large.
ACKs for top commit:
Sjors:
tACK cccc1e70b8
achow101:
ACK cccc1e70b8
laanwj:
Code review ACK cccc1e70b8
ajtowns:
ACK cccc1e70b8 ; code review; wrote a "getblockscriptflags" rpc to quickly check that blocks just had bit 17 (taproot) added; review of earlier revisions had established non-exception blocks do validate with taproot rules enabled.
jamesob:
ACK cccc1e70b8 ([`jamesob/ackr/23536.1.MarcoFalke.enforce_taproot_script_f`](https://github.com/jamesob/bitcoin/tree/ackr/23536.1.MarcoFalke.enforce_taproot_script_f))
Tree-SHA512: 00044de68939caef6420ffd588c1291c041a8b397c80a3df1e3e3487fbeae1821d23975c51c95e44e774558db76f943b00b4e27cbd0213f64a9253116dc6edde
This just calls through to AcceptToMemoryPool() internally, and is currently unused.
Also add a new transaction validation failure reason TX_NO_MEMPOOL to
indicate that there is no mempool.
The COIN constant is critical in understanding Bitcoin's supply, but what it represents isn't clear from the name of the constant. Adding a comment clarifies the meaning of the constant for future readers.
fa621ededd refactor: Pass script verify flags as uint32_t (MarcoFalke)
Pull request description:
The flags are cast to unsigned in the interpreter anyway, so avoid the confusion (and fuzz crashes) by just passing them as unsigned from the beginning.
Also, the flags are often inverted bit-wise with the `~` operator, which also works on signed integers, but might cause confusion as the sign bit is flipped.
Fixes#22233
ACKs for top commit:
theStack:
Concept and code review ACK fa621ededd
kristapsk:
ACK fa621ededd
jonatack:
ACK fa621ededd
Tree-SHA512: ea0720f32f823fa7f075309978672aa39773c6019d12b6c1c9d611fc1983a76115b7fe2a28d50814673bb6415c311ccc05b99d6e871575fb6900faf75ed17769
