Re: [PATCH v2] Document /proc/pid PID reuse behavior

From: Michal Hocko <mhocko@kernel.org>
To: Martin Steigerwald <martin@lichtvoll.de>
Cc: Daniel Colascione <dancol@google.com>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	rppt@linux.ibm.com, Tim Murray <timmurray@google.com>,
	Joel Fernandes <joelaf@google.com>,
	Suren Baghdasaryan <surenb@google.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Andrew Morton <akpm@linux-foundation.org>,
	Roman Gushchin <guro@fb.com>,
	Mike Rapoport <rppt@linux.vnet.ibm.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	"Dennis Zhou (Facebook)" <dennisszhou@gmail.com>,
	Prashant Dhamdhere <pdhamdhe@redhat.com>,
	"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>
Subject: Re: [PATCH v2] Document /proc/pid PID reuse behavior
Date: Thu, 8 Nov 2018 14:25:12 +0100	[thread overview]
Message-ID: <20181108132512.GZ27423@dhcp22.suse.cz> (raw)
In-Reply-To: <4536090.43ZsV6LvYe@merkaba>

On Wed 07-11-18 18:04:59, Martin Steigerwald wrote:
> Michal Hocko - 07.11.18, 17:00:
> > > > otherwise anybody could simply DoS the system
> > > > by consuming all available pids.
> > > 
> > > People can do that today using the instrument of terror widely known
> > > as fork(2). The only thing standing between fork(2) and a full
> > > process table is RLIMIT_NPROC.
> > 
> > not really. If you really do care about pid space depletion then you
> > should use pid cgroup controller.
> 
> Its not quite on-topic, but I am curious now: AFAIK PID limit is 16 
> bits. Right? Could it be raised to 32 bits? I bet it would be a major 
> change throughout different parts of the kernel.
> 
> 16 bits sound a bit low these days, not only for PIDs, but also for 
> connections / ports.

Do you have any specific example of the pid space exhaustion? Well
except for a fork bomb attacks that could be mitigated by the pid cgroup
controller.
-- 
Michal Hocko
SUSE Labs