guard negative value_size in memcache PopStore

src/brpc/memcache.cpp

@@ -503,8 +503,12 @@ bool MemcacheResponse::PopStore(uint8_t command, uint64_t* cas_value) {
         - (int)header.key_length;
     if (header.status != (uint16_t)STATUS_SUCCESS) {
         _buf.pop_front(sizeof(header) + header.extras_length + header.key_length);
-        _err.clear();
-        _buf.cutn(&_err, value_size);
+        if (value_size < 0) {
+            butil::string_printf(&_err, "value_size=%d is negative", value_size);
+        } else {
+            _err.clear();
+            _buf.cutn(&_err, value_size);
+        }
         return false;
     }
     LOG_IF(ERROR, value_size != 0) << "STORE response must not have value, actually="

test/brpc_memcache_unittest.cpp

@@ -62,6 +62,33 @@ TEST(MemcacheParserTest, RejectOversizedResponseBeforeBufferingBody) {
 
 }
 
+TEST(MemcacheParserTest, PopStoreRejectsNegativeValueSize) {
+    // A STORE error response whose extras_length + key_length exceeds
+    // total_body_length makes value_size negative. PopStore used to pass that
+    // straight to cutn(&_err, value_size); the negative value became a huge
+    // size_t and drained the rest of the (pipelined) buffer into the error
+    // string. The sibling parsers PopGet/PopCounter/PopVersion already guard
+    // value_size < 0; PopStore must do the same.
+    brpc::policy::MemcacheResponseHeader header = {};
+    header.magic = brpc::policy::MC_MAGIC_RESPONSE;
+    header.command = brpc::policy::MC_BINARY_SET;
+    header.status = 1;                 // non-zero: error response
+    header.extras_length = 1;          // claims extras...
+    header.key_length = 0;
+    header.total_body_length = 0;      // ...but body carries none -> value_size = -1
+
+    brpc::MemcacheResponse response;
+    response.raw_buffer().append(&header, sizeof(header));
+    // Bytes of a following pipelined response that must not leak into _err.
+    const char next_response[] = "SECRET-NEXT-RESPONSE";
+    response.raw_buffer().append(next_response, sizeof(next_response) - 1);
+
+    uint64_t cas_value = 0;
+    ASSERT_FALSE(response.PopSet(&cas_value));
+    ASSERT_EQ("value_size=-1 is negative", response.LastError());
+    ASSERT_EQ(std::string::npos, response.LastError().find("RESPONSE"));
+}
+
 static pthread_once_t download_memcached_once = PTHREAD_ONCE_INIT;
 static pid_t g_mc_pid = -1;