MaxTurnIns Bypass Race Condition

[daknob]

A bypass for the maxturnins argument on LIMITS file has been found possible under certain conditions.
More specifically, a user that has initiated a turnin that is legal in terms of quota can finalise the submission even if the course changes the maxturnins during the process of submission.
Steps to reproduce:

1. Run turnin assignment@course file.c as user and finalise the turn in
2. Run turnin assignment@course file.c as user and wait before pressing the final y.
3. Run echo "maxturnins 1" > ~/TURNIN/assignment/LIMITSas course.
4. Press y as user on the second turnin.

Abuse of this race condition is detectable through the LOGFILE and SHA256 since it marks the submission sequentially, even if it's over the maximum allowed limit.

[daknob]

DaKnOb added dofixitlazydev label

[daknob]

It has been discovered that the same issue exists with maxfiles, maxkbytes and binary as well.