Fix authority fuzzing failures

src/core/ext/filters/http/client_authority_filter.cc

@@ -97,8 +97,15 @@ grpc_error* init_channel_elem(grpc_channel_element* elem,
         "channels must explicity specify a value for this argument.");
     abort();
   }
-  chand->default_authority = grpc_slice_from_copied_string(
-      grpc_channel_arg_get_string(default_authority_arg));
+  const char* default_authority_str =
+      grpc_channel_arg_get_string(default_authority_arg);
+  if (default_authority_str == nullptr) {
+    gpr_log(GPR_ERROR,
+            "GRPC_ARG_DEFAULT_AUTHORITY channel arg. must be a string.");
+    abort();
+  }
+  chand->default_authority =
+      grpc_slice_from_copied_string(default_authority_str);
   GPR_ASSERT(!args->is_last);
   return GRPC_ERROR_NONE;
 }

src/core/lib/surface/channel.cc

@@ -167,7 +167,7 @@ static grpc_core::UniquePtr<char> get_default_authority(
       has_default_authority = true;
     } else if (0 == strcmp(input_args->args[i].key,
                            GRPC_SSL_TARGET_NAME_OVERRIDE_ARG)) {
-      ssl_override = input_args->args[i].value.string;
+      ssl_override = grpc_channel_arg_get_string(&input_args->args[i]);
     }
   }
   if (!has_default_authority && ssl_override != nullptr) {

tools/run_tests/generated/tests.json

@@ -104488,6 +104488,75 @@
     ], 
     "uses_polling": false
   }, 
+  {
+    "args": [
+      "test/core/end2end/fuzzers/api_fuzzer_corpus/clusterfuzz-testcase-api_fuzzer-5406804084260864"
+    ], 
+    "ci_platforms": [
+      "linux"
+    ], 
+    "cpu_cost": 0.1, 
+    "exclude_configs": [
+      "tsan"
+    ], 
+    "exclude_iomgrs": [
+      "uv"
+    ], 
+    "flaky": false, 
+    "language": "c", 
+    "name": "api_fuzzer_one_entry", 
+    "platforms": [
+      "mac", 
+      "linux"
+    ], 
+    "uses_polling": false
+  }, 
+  {
+    "args": [
+      "test/core/end2end/fuzzers/api_fuzzer_corpus/clusterfuzz-testcase-api_fuzzer-5471994809155584"
+    ], 
+    "ci_platforms": [
+      "linux"
+    ], 
+    "cpu_cost": 0.1, 
+    "exclude_configs": [
+      "tsan"
+    ], 
+    "exclude_iomgrs": [
+      "uv"
+    ], 
+    "flaky": false, 
+    "language": "c", 
+    "name": "api_fuzzer_one_entry", 
+    "platforms": [
+      "mac", 
+      "linux"
+    ], 
+    "uses_polling": false
+  }, 
+  {
+    "args": [
+      "test/core/end2end/fuzzers/api_fuzzer_corpus/clusterfuzz-testcase-api_fuzzer-6609852341157888"
+    ], 
+    "ci_platforms": [
+      "linux"
+    ], 
+    "cpu_cost": 0.1, 
+    "exclude_configs": [
+      "tsan"
+    ], 
+    "exclude_iomgrs": [
+      "uv"
+    ], 
+    "flaky": false, 
+    "language": "c", 
+    "name": "api_fuzzer_one_entry", 
+    "platforms": [
+      "mac", 
+      "linux"
+    ], 
+    "uses_polling": false
+  }, 
   {
     "args": [
       "test/core/end2end/fuzzers/api_fuzzer_corpus/clusterfuzz-testcase-minimized-4688823906729984"