log: Add rate limiting to LogPrintf, LogInfo, LogWarning, LogError, LogPrintLevel

To mitigate disk-filling attacks caused by unsafe usages of LogPrintf and
friends, we rate-limit them by passing a should_ratelimit bool that
eventually makes its way to LogPrintStr which may call
LogRateLimiter::Consume. The rate limiting is accomplished by
adding a LogRateLimiter member to BCLog::Logger which tracks source
code locations for the given logging window.

Every hour, a source location can log up to 1MiB of data. Source
locations that exceed the limit will have their logs suppressed for the
rest of the window determined by m_limiter.

This change affects the public LogPrintLevel function if called with
a level >= BCLog::Level::Info.

The UpdateTipLog function has been changed to use the private LogPrintLevel_
macro with should_ratelimit set to false. This allows UpdateTipLog to log
during IBD without hitting the rate limit.

Note that on restart, a source location that was rate limited before the
restart will be able to log until it hits the rate limit again.

Co-Authored-By: Niklas Gogge <n.goeggi@gmail.com>
Co-Authored-By: stickies-v <stickies-v@protonmail.com>

Author: 3 people

src/init.cpp

@@ -1378,6 +1378,11 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
         }
     }, std::chrono::minutes{5});
 
+    LogInstance().SetRateLimiting(std::make_unique<BCLog::LogRateLimiter>(
+        [&scheduler](auto func, auto window) { scheduler.scheduleEvery(std::move(func), window); },
+        BCLog::RATELIMIT_MAX_BYTES,
+        1h));
+
     assert(!node.validation_signals);
     node.validation_signals = std::make_unique<ValidationSignals>(std::make_unique<SerialTaskRunner>(scheduler));
     auto& validation_signals = *node.validation_signals;

src/logging.cpp

@@ -75,7 +75,7 @@ bool BCLog::Logger::StartLogging()
     // dump buffered messages from before we opened the log
     m_buffering = false;
     if (m_buffer_lines_discarded > 0) {
-        LogPrintStr_(strprintf("Early logging buffer overflowed, %d log lines discarded.\n", m_buffer_lines_discarded), std::source_location::current(), BCLog::ALL, Level::Info);
+        LogPrintStr_(strprintf("Early logging buffer overflowed, %d log lines discarded.\n", m_buffer_lines_discarded), std::source_location::current(), BCLog::ALL, Level::Info, /*should_ratelimit=*/false);
     }
     while (!m_msgs_before_open.empty()) {
         const auto& buflog = m_msgs_before_open.front();
@@ -412,13 +412,14 @@ void BCLog::Logger::FormatLogStrInPlace(std::string& str, BCLog::LogFlags catego
     str.insert(0, LogTimestampStr(now, mocktime));
 }
 
-void BCLog::Logger::LogPrintStr(std::string_view str, std::source_location&& source_loc, BCLog::LogFlags category, BCLog::Level level)
+void BCLog::Logger::LogPrintStr(std::string_view str, std::source_location&& source_loc, BCLog::LogFlags category, BCLog::Level level, bool should_ratelimit)
 {
     StdLockGuard scoped_lock(m_cs);
-    return LogPrintStr_(str, std::move(source_loc), category, level);
+    return LogPrintStr_(str, std::move(source_loc), category, level, should_ratelimit);
 }
 
-void BCLog::Logger::LogPrintStr_(std::string_view str, std::source_location&& source_loc, BCLog::LogFlags category, BCLog::Level level)
+// NOLINTNEXTLINE(misc-no-recursion)
+void BCLog::Logger::LogPrintStr_(std::string_view str, std::source_location&& source_loc, BCLog::LogFlags category, BCLog::Level level, bool should_ratelimit)
 {
     std::string str_prefixed = LogEscapeMessage(str);
 
@@ -451,6 +452,28 @@ void BCLog::Logger::LogPrintStr_(std::string_view str, std::source_location&& so
     }
 
     FormatLogStrInPlace(str_prefixed, category, level, source_loc, util::ThreadGetInternalName(), SystemClock::now(), GetMockTime());
+    bool ratelimit{false};
+    if (should_ratelimit && m_limiter) {
+        auto status{m_limiter->Consume(source_loc, str_prefixed)};
+        if (status == BCLog::LogRateLimiter::Status::NEWLY_SUPPRESSED) {
+            // NOLINTNEXTLINE(misc-no-recursion)
+            LogPrintStr_(strprintf(
+                             "Excessive logging detected from %s:%d (%s): >%d bytes logged during "
+                             "the last time window of %is. Suppressing logging to disk from this "
+                             "source location until time window resets. Console logging "
+                             "unaffected. Last log entry.\n",
+                             source_loc.file_name(), source_loc.line(), source_loc.function_name(),
+                             m_limiter->m_max_bytes,
+                             Ticks<std::chrono::seconds>(m_limiter->m_reset_window)),
+                         std::source_location::current(), LogFlags::ALL, Level::Warning, /*should_ratelimit=*/false); // with should_ratelimit=false, this cannot lead to infinite recursion
+        }
+        ratelimit = status == BCLog::LogRateLimiter::Status::STILL_SUPPRESSED;
+        // To avoid confusion caused by dropped log messages when debugging an issue,
+        // we prefix log lines with "[*]" when there are any suppressed source locations.
+        if (m_limiter->SuppressionsActive()) {
+            str_prefixed.insert(0, "[*] ");
+        }
+    }
 
     if (m_print_to_console) {
         // print to console
@@ -460,7 +483,7 @@ void BCLog::Logger::LogPrintStr_(std::string_view str, std::source_location&& so
     for (const auto& cb : m_print_callbacks) {
         cb(str_prefixed);
     }
-    if (m_print_to_file) {
+    if (m_print_to_file && !ratelimit) {
         assert(m_fileout != nullptr);
 
         // reopen the log file, if requested
@@ -530,7 +553,7 @@ void BCLog::LogRateLimiter::Reset()
         uint64_t dropped_bytes{counter.GetDroppedBytes()};
         if (dropped_bytes == 0) continue;
         LogPrintLevel_(
-            LogFlags::ALL, Level::Info,
+            LogFlags::ALL, Level::Info, /*should_ratelimit=*/false,
             "Restarting logging from %s:%d (%s): %d bytes were dropped during the last %ss.\n",
             source_loc.file_name(), source_loc.line(), source_loc.function_name(),
             dropped_bytes, Ticks<std::chrono::seconds>(m_reset_window));

src/logging.h

@@ -200,6 +200,9 @@ namespace BCLog {
         size_t m_cur_buffer_memusage GUARDED_BY(m_cs){0};
         size_t m_buffer_lines_discarded GUARDED_BY(m_cs){0};
 
+        //! Manages the rate limiting of each log location.
+        std::unique_ptr<LogRateLimiter> m_limiter GUARDED_BY(m_cs);
+
         //! Category-specific log level. Overrides `m_log_level`.
         std::unordered_map<LogFlags, Level> m_category_log_levels GUARDED_BY(m_cs);
 
@@ -218,7 +221,7 @@ namespace BCLog {
         std::list<std::function<void(const std::string&)>> m_print_callbacks GUARDED_BY(m_cs) {};
 
         /** Send a string to the log output (internal) */
-        void LogPrintStr_(std::string_view str, std::source_location&& source_loc, BCLog::LogFlags category, BCLog::Level level)
+        void LogPrintStr_(std::string_view str, std::source_location&& source_loc, BCLog::LogFlags category, BCLog::Level level, bool should_ratelimit)
             EXCLUSIVE_LOCKS_REQUIRED(m_cs);
 
         std::string GetLogPrefix(LogFlags category, Level level) const;
@@ -237,7 +240,7 @@ namespace BCLog {
         std::atomic<bool> m_reopen_file{false};
 
         /** Send a string to the log output */
-        void LogPrintStr(std::string_view str, std::source_location&& source_loc, BCLog::LogFlags category, BCLog::Level level)
+        void LogPrintStr(std::string_view str, std::source_location&& source_loc, BCLog::LogFlags category, BCLog::Level level, bool should_ratelimit)
             EXCLUSIVE_LOCKS_REQUIRED(!m_cs);
 
         /** Returns whether logs will be written to any output */
@@ -267,6 +270,12 @@ namespace BCLog {
         /** Only for testing */
         void DisconnectTestLogger() EXCLUSIVE_LOCKS_REQUIRED(!m_cs);
 
+        void SetRateLimiting(std::unique_ptr<LogRateLimiter>&& limiter) EXCLUSIVE_LOCKS_REQUIRED(!m_cs)
+        {
+            StdLockGuard scoped_lock(m_cs);
+            m_limiter = std::move(limiter);
+        }
+
         /** Disable logging
          * This offers a slight speedup and slightly smaller memory usage
          * compared to leaving the logging system in its default state.
@@ -334,7 +343,7 @@ static inline bool LogAcceptCategory(BCLog::LogFlags category, BCLog::Level leve
 bool GetLogCategory(BCLog::LogFlags& flag, std::string_view str);
 
 template <typename... Args>
-inline void LogPrintFormatInternal(std::source_location&& source_loc, const BCLog::LogFlags flag, const BCLog::Level level, util::ConstevalFormatString<sizeof...(Args)> fmt, const Args&... args)
+inline void LogPrintFormatInternal(std::source_location&& source_loc, const BCLog::LogFlags flag, const BCLog::Level level, const bool should_ratelimit, util::ConstevalFormatString<sizeof...(Args)> fmt, const Args&... args)
 {
     if (LogInstance().Enabled()) {
         std::string log_msg;
@@ -343,32 +352,38 @@ inline void LogPrintFormatInternal(std::source_location&& source_loc, const BCLo
         } catch (tinyformat::format_error& fmterr) {
             log_msg = "Error \"" + std::string{fmterr.what()} + "\" while formatting log message: " + fmt.fmt;
         }
-        LogInstance().LogPrintStr(log_msg, std::move(source_loc), flag, level);
+        LogInstance().LogPrintStr(log_msg, std::move(source_loc), flag, level, should_ratelimit);
     }
 }
 
-#define LogPrintLevel_(category, level, ...) LogPrintFormatInternal(std::source_location::current(), category, level, __VA_ARGS__)
+#define LogPrintLevel_(category, level, should_ratelimit, ...) LogPrintFormatInternal(std::source_location::current(), category, level, should_ratelimit, __VA_ARGS__)
 
-// Log unconditionally.
+// Log unconditionally. Uses basic rate limiting to mitigate disk filling attacks.
 // Be conservative when using functions that unconditionally log to debug.log!
 // It should not be the case that an inbound peer can fill up a user's storage
 // with debug.log entries.
-#define LogInfo(...) LogPrintLevel_(BCLog::LogFlags::ALL, BCLog::Level::Info, __VA_ARGS__)
-#define LogWarning(...) LogPrintLevel_(BCLog::LogFlags::ALL, BCLog::Level::Warning, __VA_ARGS__)
-#define LogError(...) LogPrintLevel_(BCLog::LogFlags::ALL, BCLog::Level::Error, __VA_ARGS__)
+#define LogInfo(...) LogPrintLevel_(BCLog::LogFlags::ALL, BCLog::Level::Info, /*should_ratelimit=*/true, __VA_ARGS__)
+#define LogWarning(...) LogPrintLevel_(BCLog::LogFlags::ALL, BCLog::Level::Warning, /*should_ratelimit=*/true, __VA_ARGS__)
+#define LogError(...) LogPrintLevel_(BCLog::LogFlags::ALL, BCLog::Level::Error, /*should_ratelimit=*/true, __VA_ARGS__)
 
 // Deprecated unconditional logging.
 #define LogPrintf(...) LogInfo(__VA_ARGS__)
 
 // Use a macro instead of a function for conditional logging to prevent
 // evaluating arguments when logging for the category is not enabled.
 
-// Log conditionally, prefixing the output with the passed category name and severity level.
-#define LogPrintLevel(category, level, ...)               \
-    do {                                                  \
-        if (LogAcceptCategory((category), (level))) {     \
-            LogPrintLevel_(category, level, __VA_ARGS__); \
-        }                                                 \
+// Log by prefixing the output with the passed category name and severity level. This can either
+// log conditionally if the category is allowed or unconditionally if level >= BCLog::Level::Info
+// is passed. If this function logs unconditionally, logging to disk is rate-limited. This is
+// important so that callers don't need to worry about accidentally introducing a disk-fill
+// vulnerability if level >= Info is used. Additionally, users specifying -debug are assumed to be
+// developers or power users who are aware that -debug may cause excessive disk usage due to logging.
+#define LogPrintLevel(category, level, ...)                           \
+    do {                                                              \
+        if (LogAcceptCategory((category), (level))) {                 \
+            bool rate_limit{level >= BCLog::Level::Info};             \
+            LogPrintLevel_(category, level, rate_limit, __VA_ARGS__); \
+        }                                                             \
     } while (0)
 
 // Log conditionally, prefixing the output with the passed category name.

src/test/logging_tests.cpp

@@ -6,6 +6,7 @@
 #include <logging.h>
 #include <logging/timer.h>
 #include <scheduler.h>
+#include <test/util/logging.h>
 #include <test/util/setup_common.h>
 #include <tinyformat.h>
 #include <util/fs.h>
@@ -15,8 +16,10 @@
 #include <chrono>
 #include <fstream>
 #include <future>
+#include <ios>
 #include <iostream>
 #include <source_location>
+#include <string>
 #include <unordered_map>
 #include <utility>
 #include <vector>
@@ -113,7 +116,7 @@ BOOST_FIXTURE_TEST_CASE(logging_LogPrintStr, LogSetup)
     std::vector<std::string> expected;
     for (auto& [msg, category, level, prefix, loc] : cases) {
         expected.push_back(tfm::format("[%s:%s] [%s] %s%s", util::RemovePrefix(loc.file_name(), "./"), loc.line(), loc.function_name(), prefix, msg));
-        LogInstance().LogPrintStr(msg, std::move(loc), category, level);
+        LogInstance().LogPrintStr(msg, std::move(loc), category, level, /*should_ratelimit=*/false);
     }
     std::ifstream file{tmp_log_path};
     std::vector<std::string> log_lines;
@@ -366,4 +369,106 @@ BOOST_AUTO_TEST_CASE(logging_log_limit_stats)
     BOOST_CHECK_EQUAL(counter.GetDroppedBytes(), 500ull);
 }
 
+void LogFromLocation(int location, std::string message)
+{
+    switch (location) {
+    case 0:
+        LogInfo("%s\n", message);
+        break;
+    case 1:
+        LogInfo("%s\n", message);
+        break;
+    case 2:
+        LogPrintLevel(BCLog::LogFlags::NONE, BCLog::Level::Info, "%s\n", message);
+        break;
+    case 3:
+        LogPrintLevel(BCLog::LogFlags::ALL, BCLog::Level::Info, "%s\n", message);
+        break;
+    }
+}
+
+void LogFromLocationAndExpect(int location, std::string message, std::string expect)
+{
+    ASSERT_DEBUG_LOG(expect);
+    LogFromLocation(location, message);
+}
+
+BOOST_FIXTURE_TEST_CASE(logging_filesize_rate_limit, LogSetup)
+{
+    bool prev_log_timestamps = LogInstance().m_log_timestamps;
+    LogInstance().m_log_timestamps = false;
+    bool prev_log_sourcelocations = LogInstance().m_log_sourcelocations;
+    LogInstance().m_log_sourcelocations = false;
+    bool prev_log_threadnames = LogInstance().m_log_threadnames;
+    LogInstance().m_log_threadnames = false;
+
+    CScheduler scheduler{};
+    scheduler.m_service_thread = std::thread([&] { scheduler.serviceQueue(); });
+    auto sched_func = [&scheduler](auto func, auto window) { scheduler.scheduleEvery(std::move(func), window); };
+    auto limiter = std::make_unique<BCLog::LogRateLimiter>(sched_func, 1024 * 1024, 20s);
+    LogInstance().SetRateLimiting(std::move(limiter));
+
+    // Log 1024-character lines (1023 plus newline) to make the math simple.
+    std::string log_message(1023, 'a');
+
+    std::string utf8_path{LogInstance().m_file_path.utf8string()};
+    const char* log_path{utf8_path.c_str()};
+
+    // Use GetFileSize because fs::file_size may require a flush to be accurate.
+    std::streamsize log_file_size{static_cast<std::streamsize>(GetFileSize(log_path))};
+
+    // Logging 1 MiB should be allowed.
+    for (int i = 0; i < 1024; ++i) {
+        LogFromLocation(0, log_message);
+    }
+    BOOST_CHECK_MESSAGE(log_file_size < GetFileSize(log_path), "should be able to log 1 MiB from location 0");
+
+    log_file_size = GetFileSize(log_path);
+
+    BOOST_CHECK_NO_THROW(LogFromLocationAndExpect(0, log_message, "Excessive logging detected"));
+    BOOST_CHECK_MESSAGE(log_file_size < GetFileSize(log_path), "the start of the suppression period should be logged");
+
+    log_file_size = GetFileSize(log_path);
+    for (int i = 0; i < 1024; ++i) {
+        LogFromLocation(0, log_message);
+    }
+
+    BOOST_CHECK_MESSAGE(log_file_size == GetFileSize(log_path), "all further logs from location 0 should be dropped");
+
+    BOOST_CHECK_THROW(LogFromLocationAndExpect(1, log_message, "Excessive logging detected"), std::runtime_error);
+    BOOST_CHECK_MESSAGE(log_file_size < GetFileSize(log_path), "location 1 should be unaffected by other locations");
+
+    log_file_size = GetFileSize(log_path);
+    {
+        ASSERT_DEBUG_LOG("Restarting logging");
+        MockForwardAndSync(scheduler, 1min);
+    }
+
+    BOOST_CHECK_MESSAGE(log_file_size < GetFileSize(log_path), "the end of the suppression period should be logged");
+
+    BOOST_CHECK_THROW(LogFromLocationAndExpect(1, log_message, "Restarting logging"), std::runtime_error);
+
+    // Attempt to log 1MiB from location 2 and 1MiB from location 3. These exempt locations should be allowed to log
+    // without limit.
+    log_file_size = GetFileSize(log_path);
+    for (int i = 0; i < 1024; ++i) {
+        BOOST_CHECK_THROW(LogFromLocationAndExpect(2, log_message, "Excessive logging detected"), std::runtime_error);
+    }
+
+    BOOST_CHECK_MESSAGE(log_file_size < GetFileSize(log_path), "location 2 should be exempt from rate limiting");
+
+    log_file_size = GetFileSize(log_path);
+    for (int i = 0; i < 1024; ++i) {
+        BOOST_CHECK_THROW(LogFromLocationAndExpect(3, log_message, "Excessive logging detected"), std::runtime_error);
+    }
+
+    BOOST_CHECK_MESSAGE(log_file_size < GetFileSize(log_path), "location 3 should be exempt from rate limiting");
+
+    LogInstance().m_log_timestamps = prev_log_timestamps;
+    LogInstance().m_log_sourcelocations = prev_log_sourcelocations;
+    LogInstance().m_log_threadnames = prev_log_threadnames;
+    scheduler.stop();
+    LogInstance().SetRateLimiting(nullptr);
+}
+
 BOOST_AUTO_TEST_SUITE_END()

src/validation.cpp

@@ -2976,15 +2976,17 @@ static void UpdateTipLog(
 {
 
     AssertLockHeld(::cs_main);
-    LogPrintf("%s%s: new best=%s height=%d version=0x%08x log2_work=%f tx=%lu date='%s' progress=%f cache=%.1fMiB(%utxo)%s\n",
-        prefix, func_name,
-        tip->GetBlockHash().ToString(), tip->nHeight, tip->nVersion,
-        log(tip->nChainWork.getdouble()) / log(2.0), tip->m_chain_tx_count,
-        FormatISO8601DateTime(tip->GetBlockTime()),
-        chainman.GuessVerificationProgress(tip),
-        coins_tip.DynamicMemoryUsage() * (1.0 / (1 << 20)),
-        coins_tip.GetCacheSize(),
-        !warning_messages.empty() ? strprintf(" warning='%s'", warning_messages) : "");
+
+    // Disable rate limiting in LogPrintLevel_ so this source location may log during IBD.
+    LogPrintLevel_(BCLog::LogFlags::ALL, BCLog::Level::Info, /*should_ratelimit=*/false, "%s%s: new best=%s height=%d version=0x%08x log2_work=%f tx=%lu date='%s' progress=%f cache=%.1fMiB(%utxo)%s\n",
+                   prefix, func_name,
+                   tip->GetBlockHash().ToString(), tip->nHeight, tip->nVersion,
+                   log(tip->nChainWork.getdouble()) / log(2.0), tip->m_chain_tx_count,
+                   FormatISO8601DateTime(tip->GetBlockTime()),
+                   chainman.GuessVerificationProgress(tip),
+                   coins_tip.DynamicMemoryUsage() * (1.0 / (1 << 20)),
+                   coins_tip.GetCacheSize(),
+                   !warning_messages.empty() ? strprintf(" warning='%s'", warning_messages) : "");
 }
 
 void Chainstate::UpdateTip(const CBlockIndex* pindexNew)