cuckoocache: Check for uint32 overflow in setup_bytes

This fixes an potential overflow which existed prior to this patchset.

If CuckooCache::cache<Element, Hash>::setup_bytes is called with a
`size_t bytes` which, when divided by sizeof(Element), does not fit into
an uint32_t, the implicit conversion to uint32_t in the call to setup
will result in an overflow.

At least on x86_64, this overflow is possible:

static_assert(std::numeric_limits<size_t>::max() / 32 <= std::numeric_limits<uint32_t>::max());
static_assert(std::numeric_limits<size_t>::max() / 4 <= std::numeric_limits<uint32_t>::max());

This commit detects such cases and signals to callers that the `size_t
bytes` input is too large.

1 files changed, 2 insertions, 1 deletions

diff --git a/src/validation.cpp b/src/validation.cpp
index 4d174a4b16..73a6e46cc4 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -1669,8 +1669,9 @@ bool InitScriptExecutionCache() {
     size_t nMaxCacheSize = std::max((int64_t)0, gArgs.GetIntArg("-maxsigcachesize", DEFAULT_MAX_SIG_CACHE_SIZE) / 2) * ((size_t) 1 << 20);
 
     auto setup_results = g_scriptExecutionCache.setup_bytes(nMaxCacheSize);
+    if (!setup_results) return false;
 
-    const auto [num_elems, approx_size_bytes] = setup_results;
+    const auto [num_elems, approx_size_bytes] = *setup_results;
     LogPrintf("Using %zu MiB out of %zu/2 requested for script execution cache, able to store %zu elements\n",
               approx_size_bytes >> 20, (nMaxCacheSize * 2) >> 20, num_elems);
     return true;