From: Peter Hurley <peter@hurleysoftware.com>
Date: Thu, 16 Oct 2014 18:59:47 +0000 (-0400)
Subject: tty: Fix multiple races when setting the controlling terminal
X-Git-Tag: omap-for-v3.19/fixes-rc1~86^2~208
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2c411c11020ff356748268ca9cae4c1b4c410f00;p=pandora-kernel.git

tty: Fix multiple races when setting the controlling terminal

Claim a read lock on the tasklist_lock while setting the controlling
terminal for the session leader. This fixes multiple races:
1. task_pgrp() and task_session() cannot be safely dereferenced, such
   as passing to get_pid(), without holding either rcu_read_lock() or
   tasklist_lock
2. setsid() unwisely allows any thread in the thread group to
   make the thread group leader the session leader; this makes the
   unlocked reads of ->signal->leader and signal->tty potentially
   unordered, stale or even have spurious values.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Reviewed-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

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