backport: Shut down if trying to connect a corrupted block (#1126)

Manual backport of bitcoin#0e7c52dc6cbb8fd881a0dd57a6167a812fe71dc4

Fixes issue #1087

Commit message by author sdaftuar:
The call to CheckBlock() in ConnectBlock() is redundant with calls to it
prior to storing a block on disk. If CheckBlock() fails with an error
indicating the block is potentially corrupted, then shut down
immediately, as this is an indication that the node is experiencing
hardware issues.  (If we didn't shut down, we could go into an infinite
loop trying to reconnect this same bad block, as we're not setting the
block's status to FAILED in the case where there is potential
corruption.)

If CheckBlock() fails for some other reason, we'll end up flagging this
block as bad (perhaps some prior software version "let a bad block in",
as the comment indicates), and not trying to connect it again, so this
case should be properly handled.

src/validation.cpp

@@ -2416,9 +2416,15 @@ static bool ConnectBlock(const CBlock& block, CValidationState& state, CBlockInd
     int64_t nTimeStart = GetTimeMicros();
 
     // Check it again in case a previous version let a bad block in
-    if (!CheckBlock(block, state, chainparams.GetConsensus(), !fJustCheck, !fJustCheck)) // Force the check of asset duplicates when connecting the block
+    if (!CheckBlock(block, state, chainparams.GetConsensus(), !fJustCheck, !fJustCheck)) { // Force the check of asset duplicates when connecting the block
+        if (state.CorruptionPossible()) {
+            // We don't write down blocks to disk if they may have been
+            // corrupted, so this should be impossible unless we're having hardware
+            // problems.
+            return AbortNode(state, "Corrupt block found indicating potential hardware failure; shutting down");
+        }
         return error("%s: Consensus::CheckBlock: %s", __func__, FormatStateMessage(state));
-
+    }
     // verify that the view's current state corresponds to the previous block
     uint256 hashPrevBlock = pindex->pprev == nullptr ? uint256() : pindex->pprev->GetBlockHash();
     assert(hashPrevBlock == view.GetBestBlock());