Nomad does not validate task names against alloc as a reserved directory name, which breaks filesystem isolation between tasks.

The Allocation Working Directory looks like this:

  /
    task1/          
    task2/         
    alloc/          

Now if I choose to name a task alloc, everything gets messed up in exactly the expected way, which is that alloc the task directory and alloc the shared directory are the same, and task1 and task2 can read/write that task's stuff. I tried this.

Calling this a security issue would be a stretch because it does require much deliberate effort by the operator to make happen, but it doesn't seem quite right either, since it is an actual broken promise about file system isolation.

Maybe alloc should simply not be a permitted name for a task?