Re: [RFC] [Patch 0/21] Non disruptive application core dump infrastructure

["Suzuki K. Poulose" <suzuki@in.ibm.com>]

On Tue, 14 Dec 2010 07:49:37 -0800
Linus Torvalds <torvalds@linux-foundation.org> wrote:

> On Tue, Dec 14, 2010 at 1:52 AM, Suzuki K. Poulose <suzuki@in.ibm.com> wrote:
> >
> > This is series of patches implementing an infrastructure for capturing the core
> > of an application without disrupting its process semantics.
> >
> > The infrastructure makes use of the freezer subsystem in kernel to freeze the
> > threads and then collect the information to generate  the core.
> 
> This seems to be a fundamentally flawed approach.
> 
> From a security standpoint, it looks like a total disaster. A frozen
> process is really hard to get rid of, so it looks like an obvious DoS
> attack to just create lots of processes, then sneakily freeze them
> all, and then laugh at the poor system admin who has no idea what's
> going on. While frozen, the things are basically unkillable but look
> entirely normal, no?

You are right. We need a simple mechanism to hold the threads, so that we 
could collect the register information of the process without affecting its 
process semantics (eg, signals etc.). The suggestion by Kamezawa-san -a 
freeze state variant which allows SIGKILL - is one possibility.

I'd be very glad not using the freezer if there is a neat way to accomplish 
this without the undesired side effects. Tejun's ptrace enhancement would 
still require a userland program to control it(gcore); something contained 
in the kernel would be ideal.


Thanks

Suzuki

> 
>                                      Linus