8297242: Use-after-free during library unloading on Linux

Backport-of: 6f06f440bcf8a5db379b80e8765af38a15449356

Author: MBaesken

src/hotspot/os/posix/os_posix.cpp

@@ -698,9 +698,20 @@ void* os::dll_lookup(void* handle, const char* name) {
 }
 
 void os::dll_unload(void *lib) {
-  const char* l_path = LINUX_ONLY(os::Linux::dll_path(lib))
-                       NOT_LINUX("<not available>");
-  if (l_path == NULL) l_path = "<not available>";
+  // os::Linux::dll_path returns a pointer to a string that is owned by the dynamic loader. Upon
+  // calling dlclose the dynamic loader may free the memory containing the string, thus we need to
+  // copy the string to be able to reference it after dlclose.
+  const char* l_path = NULL;
+#ifdef LINUX
+  char* l_pathdup = NULL;
+  l_path = os::Linux::dll_path(lib);
+  if (l_path != NULL) {
+    l_path = l_pathdup = os::strdup(l_path);
+  }
+#endif  // LINUX
+  if (l_path == NULL) {
+    l_path = "<not available>";
+  }
   int res = ::dlclose(lib);
 
   if (res == 0) {
@@ -718,6 +729,7 @@ void os::dll_unload(void *lib) {
     log_info(os)("Attempt to unload shared library \"%s\" [" INTPTR_FORMAT "] failed, %s",
                   l_path, p2i(lib), error_report);
   }
+  LINUX_ONLY(os::free(l_pathdup));
 }
 
 jlong os::lseek(int fd, jlong offset, int whence) {