From: Cyrill Gorcunov <gorcunov@openvz.org>
Date: Fri, 19 Oct 2012 20:56:53 +0000 (-0700)
Subject: pidns: remove recursion from free_pid_ns()
X-Git-Tag: v3.7-rc2~10^2~3
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=bbc2e3ef87851bc5430b2b4cf4ca3a2f29baeda6;p=pandora-kernel.git

pidns: remove recursion from free_pid_ns()

free_pid_ns() operates in a recursive fashion:

free_pid_ns(parent)
  put_pid_ns(parent)
    kref_put(&ns->kref, free_pid_ns);
      free_pid_ns

thus if there was a huge nesting of namespaces the userspace may trigger
avalanche calling of free_pid_ns leading to kernel stack exhausting and a
panic eventually.

This patch turns the recursion into an iterative loop.

Based on a patch by Andrew Vagin.

[akpm@linux-foundation.org: export put_pid_ns() to modules]
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Andrew Vagin <avagin@openvz.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Greg KH <greg@kroah.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

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