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new 96ce9f11 Fix bug when parsing zero-length string field in mcpack2pb
(#3450)
96ce9f11 is described below
commit 96ce9f11eef0a9d05f9ed8e910ffac7df8afa5bd
Author: Weibing Wang <[email protected]>
AuthorDate: Sun Aug 16 18:01:01 2026 +0800
Fix bug when parsing zero-length string field in mcpack2pb (#3450)
* Fix bug when parsing zero-length string field in mcpack2pb
UnparsedValue::as_string() resizes the output string to
without checking , where is the value_size of a string
field read from the input. When value_size is 0, underflows
to SIZE_MAX and resize() throws std::length_error, which is not caught
on the request path and therefore crashes the server. Reject such
malformed fields by marking the stream bad so the caller can fail the
request gracefully instead.
* Clear output string when size error
---
src/mcpack2pb/parser.cpp | 9 +++++
test/brpc_mcpack2pb_unittest.cpp | 80 ++++++++++++++++++++++++++++++++++++++++
2 files changed, 89 insertions(+)
diff --git a/src/mcpack2pb/parser.cpp b/src/mcpack2pb/parser.cpp
index 5c785dc4..92d7a220 100644
--- a/src/mcpack2pb/parser.cpp
+++ b/src/mcpack2pb/parser.cpp
@@ -577,6 +577,15 @@ double UnparsedValue::as_double(const char* var) {
}
void UnparsedValue::as_string(std::string* out, const char* var) {
+ if (_size < 1) {
+ // A string field must contain at least the trailing '\0'.
+ // Reject _size == 0 here, otherwise `_size - 1' underflows and
+ // resize() throws an uncaught exception. Clear `out' so callers
+ // that reuse the string do not keep a stale value.
+ out->clear();
+ _stream->set_bad();
+ return;
+ }
out->resize(_size - 1);
if (_stream->cutn(&(*out)[0], _size - 1) != _size - 1) {
CHECK(false) << "Not enough data for " << var;
diff --git a/test/brpc_mcpack2pb_unittest.cpp b/test/brpc_mcpack2pb_unittest.cpp
index 68de0522..6718cae9 100644
--- a/test/brpc_mcpack2pb_unittest.cpp
+++ b/test/brpc_mcpack2pb_unittest.cpp
@@ -23,6 +23,86 @@
namespace {
+TEST(Mcpack2pbParserTest, StringFieldWithZeroValueSize) {
+ // A 51-byte mcpack2 frame whose `service_name' string field has
+ // value_size == 0. This used to underflow in UnparsedValue::as_string()
+ // (resize(_size - 1) with _size == 0) and throw std::length_error, which
+ // is not caught on the request path and therefore crashes the server.
+ const unsigned char data[] = {
+ 0x10, 0x00, 0x2d, 0x00, 0x00, 0x00,
+ 0x01, 0x00, 0x00, 0x00,
+ 0xa0, 0x08, 0x1e, 0x63, 0x6f, 0x6e, 0x74, 0x65, 0x6e, 0x74, 0x00,
+ 0x01, 0x00, 0x00, 0x00,
+ 0x10, 0x00, 0x14, 0x00, 0x00, 0x00,
+ 0x01, 0x00, 0x00, 0x00,
+ 0xd0, 0x0d, 0x00, 0x73, 0x65, 0x72, 0x76, 0x69, 0x63, 0x65,
+ 0x5f, 0x6e, 0x61, 0x6d, 0x65, 0x00,
+ };
+ butil::IOBuf body;
+ body.append(data, sizeof(data));
+
+ butil::IOBufAsZeroCopyInputStream zc_stream(body);
+ mcpack2pb::InputStream stream(&zc_stream);
+ ASSERT_NE(0u, mcpack2pb::unbox(&stream));
+
+ mcpack2pb::ObjectIterator it1(&stream, body.size() -
stream.popped_bytes());
+ bool found_content = false;
+ for (; it1 != NULL; ++it1) {
+ if (it1->name == "content") {
+ found_content = true;
+ break;
+ }
+ }
+ ASSERT_TRUE(found_content);
+ ASSERT_EQ(mcpack2pb::FIELD_ARRAY, it1->value.type());
+
+ mcpack2pb::ArrayIterator it2(it1->value);
+ ASSERT_TRUE(it2 != NULL);
+ bool found_service_name = false;
+ for (mcpack2pb::ObjectIterator it3(*it2); it3 != NULL; ++it3) {
+ if (it3->name == "service_name") {
+ found_service_name = true;
+ ASSERT_EQ(mcpack2pb::FIELD_STRING, it3->value.type());
+ std::string service_name = "stale";
+ it3->value.as_string(&service_name, "service_name");
+ // A zero-sized string field must be rejected gracefully instead of
+ // throwing (resize(SIZE_MAX)) and crashing the process.
+ EXPECT_FALSE(it3->value.stream()->good());
+ // The output string must be cleared so callers that reuse the
+ // string do not keep a stale value.
+ EXPECT_TRUE(service_name.empty());
+ break;
+ }
+ }
+ ASSERT_TRUE(found_service_name);
+}
+
+TEST(Mcpack2pbParserTest, ParseStringField) {
+ // A valid object {"msg":"abc"}.
+ const unsigned char data[] = {
+ 0x10, 0x00, 0x0f, 0x00, 0x00, 0x00,
+ 0x01, 0x00, 0x00, 0x00,
+ 0xd0, 0x04, 0x04,
+ 0x6d, 0x73, 0x67, 0x00,
+ 0x61, 0x62, 0x63, 0x00,
+ };
+ butil::IOBuf body;
+ body.append(data, sizeof(data));
+
+ butil::IOBufAsZeroCopyInputStream zc_stream(body);
+ mcpack2pb::InputStream stream(&zc_stream);
+ ASSERT_NE(0u, mcpack2pb::unbox(&stream));
+
+ mcpack2pb::ObjectIterator it(&stream, body.size() - stream.popped_bytes());
+ ASSERT_TRUE(it != NULL);
+ EXPECT_EQ("msg", it->name.as_string());
+ ASSERT_EQ(mcpack2pb::FIELD_STRING, it->value.type());
+ std::string value;
+ it->value.as_string(&value, "msg");
+ EXPECT_EQ("abc", value);
+ EXPECT_TRUE(stream.good());
+}
+
TEST(Mcpack2pbParserTest, ArrayItemCountIsCappedToRemainingBytes) {
// An mcpack array whose header claims item_count = 0x7fffffff (INT32_MAX)
// but contains no actual items. The raw item_count is fed by the
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