Re: [PATCH] proc: use ns_capable instead of capable for timerslack_ns

[Benjamin Gordon]

On Thu, Oct 25, 2018 at 01:56:27PM -0500, Eric W. Biederman wrote:
> > Access to timerslack_ns is controlled by a process having CAP_SYS_NICE
> > in its effective capability set, but the current check looks in the root
> > namespace instead of the process' user namespace.  Since a process is
> > allowed to do other activities controlled by CAP_SYS_NICE inside a
> > namespace, it should also be able to adjust timerslack_ns.
> 
> The goal seems legitimate.  However the permission checks look wrong.
> 
> In particular the choice of user namespace should be
> "p->cred->user_ns".  This will limit this to tasks that have
> CAP_SYS_NICE in the same namespace as the task that is being modified.
> 
> Testing file->f_cred->user_ns it is testing whoever opened the file and
> that could be anyone.

Thanks, that seems like the right answer here.  I'll send a v2 to fix
it.

Thanks,
Benjamin