[clue-tech] Filesystem quotas circumvented

[David Anselmi]

Angelo Bertolli wrote:
> So today I tried to do this (as user angelo):
> 
> cd /
> sudo ls -lhRt > ~/lsr
> 
> And of course it starts accumulating... but somehow it was able to get 
> beyond the hard quota limit:

Basically the redirect is done before sudo runs and root isn't 
restricted by your quota.

Bash runs a simple command (like sudo above) in an execution environment 
that consists of "the shell's open files, plus any  modifications  and 
additions specified by redirections to the command" (see bash(1)).

Probably the whole process goes like this:

bash forks

the child shell closes stdout and opens ~/lsr for writing on fd 2 (which 
truncates or creates the file as needed)

the child shell execs sudo which changes to UID 0 and execs ls

So the file gets created as you (which can be a pain but isn't the 
problem here).  But then you have root writing into your file.  Does 
your quota apply to what root does?  Apparently not (no surprise).  But 
the quota is system wide, right?  So after you've created this file you 
won't be able to create or append to any more.

Dave