Re: [PATCH 3/7] seccomp_filter: Enable ftrace-based system callfiltering

[Serge E. Hallyn]

Quoting Will Drewry (wad@xxxxxxxxxxxx):
> >>  void __secure_computing(int this_syscall)
> >>  {
> >> -     int mode = current->seccomp.mode;
> >> +     int mode = -1;
> >>       int * syscall;
> >> -
> >> +     /* Do we need an RCU read lock to access current's state? */
> >
> > I'm actually confused to why you are using RCU. What are you protecting.
> > Currently, I see the state is always accessed from current->seccomp. But
> > current should not be fighting with itself.
> >
> > Maybe I'm missing something.
> 
> I'm sure it's me that's missing something.  I believe the seccomp
> pointer can be accessed from:
> - current
> - via /proc/<pid>/seccomp_filter (read-only)
> 
> Given those cases, would it make sense to ditch the RCU interface for it?

ISTM you need them to protect the reader.

-serge
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