[core] Reduce maximum number of validation errors to track (#36537)

Fuzzers were OOMing while trying to create 10k errors. This sets a sane default.

Closes #36537

COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/36537 from drfloob:less-validation-noise db835d948a
PiperOrigin-RevId: 631158900

src/core/BUILD

@@ -399,7 +399,7 @@ grpc_cc_library(
         "absl/strings",
     ],
     language = "c++",
-    deps = ["//:gpr_platform"],
+    deps = ["//:gpr"],
 )
 
 grpc_cc_library(

src/core/lib/gprpp/validation_errors.cc

@@ -14,6 +14,8 @@
 
 #include "src/core/lib/gprpp/validation_errors.h"
 
+#include <inttypes.h>
+
 #include <utility>
 
 #include "absl/status/status.h"
@@ -21,6 +23,7 @@
 #include "absl/strings/str_join.h"
 #include "absl/strings/strip.h"
 
+#include <grpc/support/log.h>
 #include <grpc/support/port_platform.h>
 
 namespace grpc_core {
@@ -34,7 +37,14 @@ void ValidationErrors::PushField(absl::string_view ext) {
 void ValidationErrors::PopField() { fields_.pop_back(); }
 
 void ValidationErrors::AddError(absl::string_view error) {
-  field_errors_[absl::StrJoin(fields_, "")].emplace_back(error);
+  auto key = absl::StrJoin(fields_, "");
+  if (field_errors_[key].size() >= max_error_count_) {
+    gpr_log(GPR_DEBUG,
+            "Ignoring validation error: too many errors found (%" PRIuPTR ")",
+            max_error_count_);
+    return;
+  }
+  field_errors_[key].emplace_back(error);
 }
 
 bool ValidationErrors::FieldHasErrors() const {

src/core/lib/gprpp/validation_errors.h

@@ -63,6 +63,9 @@ namespace grpc_core {
 // }
 class ValidationErrors {
  public:
+  // Default maximum number of errors to track per scope.
+  static constexpr size_t kMaxErrorCount = 20;
+
   // Pushes a field name onto the stack at construction and pops it off
   // of the stack at destruction.
   class ScopedField {
@@ -93,6 +96,12 @@ class ValidationErrors {
     ValidationErrors* errors_;
   };
 
+  ValidationErrors() : ValidationErrors(kMaxErrorCount) {}
+
+  // Creates a tracker that collects at most `max_error_count` errors per field.
+  explicit ValidationErrors(size_t max_error_count)
+      : max_error_count_(max_error_count) {}
+
   // Records that we've encountered an error associated with the current
   // field.
   void AddError(absl::string_view error) GPR_ATTRIBUTE_NOINLINE;
@@ -127,6 +136,8 @@ class ValidationErrors {
   // Stack of field names indicating the field that we are currently
   // validating.
   std::vector<std::string> fields_;
+
+  size_t max_error_count_;
 };
 
 }  // namespace grpc_core