parts w/o filename in Content-Disposition header are not cleaned from temp folder (skipped by StandardServletMultipartResolver)

[gbrehmer]

Affects: 6.1.12 (but can not say since when exactly, older versions are probably also affected) + Jetty 12.0.12

Parts w/o filename in content disposition header are missing in AbstractMultipartHttpServletRequest.getMultiFileMap(). Because of this part.delete() is skipped in the resolver.
The relevant logic to filter out such parts is in

spring-framework/spring-web/src/main/java/org/springframework/web/multipart/support/StandardMultipartHttpServletRequest.java

Line 101 in eff19ec

if (filename != null) {

the logic to ignore parts which are not part of the filemap is here:

spring-framework/spring-web/src/main/java/org/springframework/web/multipart/support/StandardServletMultipartResolver.java

Line 123 in eff19ec

if (request.getFile(part.getName()) != null) {

Should we cleanup those parts by ourself? Not sure whether there are other dependencies (why it should not be part of filemap e.g.) but our fix is currently to overwrite the StandardServletMultipartResolver and delete the part nevertheless its contained or not in the filemap)

[gbrehmer]

I see all related code parts are VERY old, but I guess temp folder issues are sometimes hard to find, because normally temp folders are cleaned automatically on next boot. We found it because we limited the space for temp folder to a very low size (500M) when we normally have no big uploads or file generations.
To fix the problem it would be enough to remove one of the mentioned checks/filters ;) But of course I have not all required informations/experiences with other servlet containers/use cases/corner cases etc. to make a decision like that