[fix] Prevent a signed integer overflow in timeout_encoding.cc (#32432)

Return `Timeout(kMaxHours, Unit::kHours)` if the value is about to
overflow in `DivideRoundingUp`.

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src/core/lib/transport/timeout_encoding.cc

@@ -20,6 +20,8 @@
 
 #include "src/core/lib/transport/timeout_encoding.h"
 
+#include <limits>
+
 #include "absl/base/attributes.h"
 
 #include <grpc/support/log.h>
@@ -30,7 +32,7 @@ namespace grpc_core {
 namespace {
 
 int64_t DivideRoundingUp(int64_t dividend, int64_t divisor) {
-  return (dividend + divisor - 1) / divisor;
+  return (dividend - 1 + divisor) / divisor;
 }
 
 constexpr int64_t kSecondsPerMinute = 60;
@@ -173,6 +175,9 @@ Timeout Timeout::FromMillis(int64_t millis) {
   } else if (millis < 100000) {
     int64_t value = DivideRoundingUp(millis, 100);
     if (value % 10 != 0) return Timeout(value, Unit::kHundredMilliseconds);
+  } else if (millis > std::numeric_limits<int64_t>::max() - 999) {
+    // prevent signed integer overflow.
+    return Timeout(kMaxHours, Unit::kHours);
   }
   return Timeout::FromSeconds(DivideRoundingUp(millis, 1000));
 }

test/core/end2end/fuzzers/client_fuzzer.cc

@@ -25,6 +25,7 @@
 
 #include "absl/status/statusor.h"
 #include "absl/strings/str_format.h"
+#include "absl/types/optional.h"
 
 #include <grpc/byte_buffer.h>
 #include <grpc/grpc.h>
@@ -38,6 +39,7 @@
 #include "src/core/lib/channel/channel_args_preconditioning.h"
 #include "src/core/lib/config/core_configuration.h"
 #include "src/core/lib/gprpp/crash.h"
+#include "src/core/lib/gprpp/env.h"
 #include "src/core/lib/gprpp/ref_counted_ptr.h"
 #include "src/core/lib/iomgr/endpoint.h"
 #include "src/core/lib/iomgr/exec_ctx.h"
@@ -59,7 +61,9 @@ static void* tag(intptr_t t) { return reinterpret_cast<void*>(t); }
 static void dont_log(gpr_log_func_args* /*args*/) {}
 
 extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
-  if (squelch) gpr_set_log_function(dont_log);
+  if (squelch && !grpc_core::GetEnv("GRPC_TRACE_FUZZER").has_value()) {
+    gpr_set_log_function(dont_log);
+  }
   grpc_init();
   {
     grpc_core::ExecCtx exec_ctx;