Merge bitcoin/bitcoin#27235: Avoid integer overflow in CheckDiskSpace

05eeba2 [test] Add manual prune startup test case (dergoegge)
4517419 [util] Avoid integer overflow in CheckDiskSpace (dergoegge)

Pull request description:

  Starting a fresh node with `-prune=1` causes an integer overflow to happen in `CheckDiskSpace` ([here](https://github.com/bitcoin/bitcoin/blob/f7bdcfc83f5753349018be3b5a663c8923d1a5eb/src/init.cpp#L1633-L1648)) because `nPruneTarget` is to the max `uint64_t` value.
  ```
   node1 stderr util/system.cpp:138:51: runtime error: unsigned integer overflow: 52428800 + 18446744073709551615 cannot be represented in type 'unsigned long'
      #0 0x564a482b5088 in CheckDiskSpace(fs::path const&, unsigned long) src/./src/util/system.cpp:138:51
      #1 0x564a4728dc59 in AppInitMain(node::NodeContext&, interfaces::BlockAndHeaderTipInfo*) src/./src/init.cpp:1639:14
      bitcoin-core#2 0x564a47256e6a in AppInit(node::NodeContext&, int, char**) src/./src/bitcoind.cpp:221:43
      bitcoin-core#3 0x564a47256087 in main src/./src/bitcoind.cpp:265:13
      bitcoin-core#4 0x7fcb7cbffd8f  (/lib/x86_64-linux-gnu/libc.so.6+0x29d8f) (BuildId: 69389d485a9793dbe873f0ea2c93e02efaa9aa3d)
      bitcoin-core#5 0x7fcb7cbffe3f in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e3f) (BuildId: 69389d485a9793dbe873f0ea2c93e02efaa9aa3d)
      bitcoin-core#6 0x564a471957f4 in _start (/tmp/cirrus-ci-build/ci/scratch/build/bitcoin-x86_64-pc-linux-gnu/src/bitcoind+0xca07f4) (BuildId: 035cb22302d37317a630900a15a26ecb326d395c)
  SUMMARY: UndefinedBehaviorSanitizer: unsigned-integer-overflow util/system.cpp:138:51 in
  ```

  I think side stepping the overflow for this specific case, is better than adding an exception to the UB suppresions file.

ACKs for top commit:
  MarcoFalke:
    ACK 05eeba2 🥝
  john-moffett:
    ACK 05eeba2

Tree-SHA512: 1d8e6bcb49818139f04b5ab2cbef7f9b422bf0c38a804cd532b6bd0ba4c4fd07f959ba977e59896343f213086c8ecc48180f50d006638dc84649c66ec379d58a

src/init.cpp

@@ -1631,10 +1631,11 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
 
     // On first startup, warn on low block storage space
     if (!fReindex && !fReindexChainState && chain_active_height <= 1) {
+        uint64_t assumed_chain_bytes{chainparams.AssumedBlockchainSize() * 1024 * 1024 * 1024};
         uint64_t additional_bytes_needed{
             chainman.m_blockman.IsPruneMode() ?
-                chainman.m_blockman.GetPruneTarget() :
-                chainparams.AssumedBlockchainSize() * 1024 * 1024 * 1024};
+                std::min(chainman.m_blockman.GetPruneTarget(), assumed_chain_bytes) :
+                assumed_chain_bytes};
 
         if (!CheckDiskSpace(args.GetBlocksDirPath(), additional_bytes_needed)) {
             InitWarning(strprintf(_(

test/functional/rpc_blockchain.py

@@ -69,6 +69,7 @@ def set_test_params(self):
 
     def run_test(self):
         self.wallet = MiniWallet(self.nodes[0])
+        self._test_prune_disk_space()
         self.mine_chain()
         self._test_max_future_block_time()
         self.restart_node(
@@ -100,6 +101,13 @@ def mine_chain(self):
             self.generate(self.wallet, 1)
         assert_equal(self.nodes[0].getblockchaininfo()['blocks'], HEIGHT)
 
+    def _test_prune_disk_space(self):
+        self.log.info("Test that a manually pruned node does not run into "
+                      "integer overflow on first start up")
+        self.restart_node(0, extra_args=["-prune=1"])
+        self.log.info("Avoid warning when assumed chain size is enough")
+        self.restart_node(0, extra_args=["-prune=123456789"])
+
     def _test_max_future_block_time(self):
         self.stop_node(0)
         self.log.info("A block tip of more than MAX_FUTURE_BLOCK_TIME in the future raises an error")