Daisuke Nishimura 62875332ea sched/fair: Fix small race where child->se.parent,cfs_rq might point to invalid ones ... commit 6c9a27f5da upstream. There is a small race between copy_process() and cgroup_attach_task() where child->se.parent,cfs_rq points to invalid (old) ones. parent doing fork() | someone moving the parent to another cgroup -------------------------------+--------------------------------------------- copy_process() + dup_task_struct() -> parent->se is copied to child->se. se.parent,cfs_rq of them point to old ones. cgroup_attach_task() + cgroup_task_migrate() -> parent->cgroup is updated. + cpu_cgroup_attach() + sched_move_task() + task_move_group_fair() +- set_task_rq() -> se.parent,cfs_rq of parent are updated. + cgroup_fork() -> parent->cgroup is copied to child->cgroup. (*1) + sched_fork() + task_fork_fair() -> se.parent,cfs_rq of child are accessed while they point to old ones. (*2) In the worst case, this bug can lead to "use-after-free" and cause a panic, because it's new cgroup's refcount that is incremented at (*1), so the old cgroup(and related data) can be freed before (*2). In fact, a panic caused by this bug was originally caught in RHEL6.4. BUG: unable to handle kernel NULL pointer dereference at (null) IP: [<ffffffff81051e3e>] sched_slice+0x6e/0xa0 [...] Call Trace: [<ffffffff81051f25>] place_entity+0x75/0xa0 [<ffffffff81056a3a>] task_fork_fair+0xaa/0x160 [<ffffffff81063c0b>] sched_fork+0x6b/0x140 [<ffffffff8106c3c2>] copy_process+0x5b2/0x1450 [<ffffffff81063b49>] ? wake_up_new_task+0xd9/0x130 [<ffffffff8106d2f4>] do_fork+0x94/0x460 [<ffffffff81072a9e>] ? sys_wait4+0xae/0x100 [<ffffffff81009598>] sys_clone+0x28/0x30 [<ffffffff8100b393>] stub_clone+0x13/0x20 [<ffffffff8100b072>] ? system_call_fastpath+0x16/0x1b Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/039601ceae06$733d3130$59b79390$@mxp.nes.nec.co.jp Signed-off-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>		2013-10-01 09:10:51 -07:00
..
auto_group.c	Revert "sched, autogroup: Stop going ahead if autogroup is disabled"	2012-12-10 10:59:40 -08:00
auto_group.h	Revert "sched, autogroup: Stop going ahead if autogroup is disabled"	2012-12-10 10:59:40 -08:00
clock.c	sched_clock: Prevent 64bit inatomicity on 32bit systems	2013-04-16 21:27:27 -07:00
core.c	sched: Convert BUG_ON()s in try_to_wake_up_local() to WARN_ON_ONCE()s	2013-04-25 21:19:55 -07:00
cpupri.c
cpupri.h
debug.c	sched: Remove sched_switch	2012-01-27 13:28:53 +01:00
fair.c	sched/fair: Fix small race where child->se.parent,cfs_rq might point to invalid ones	2013-10-01 09:10:51 -07:00
features.h	sched: Fix more load-balancing fallout	2012-04-26 12:54:52 +02:00
idle_task.c	sched/nohz: Rewrite and fix load-avg computation -- again	2012-07-19 08:58:56 -07:00
Makefile
rt.c	sched/rt: Use root_domain of rt_rq not current processor	2013-02-11 08:47:18 -08:00
sched.h	sched: Fix race in task_group()	2012-10-02 10:30:35 -07:00
stats.c	sched: Remove sched_switch	2012-01-27 13:28:53 +01:00
stats.h
stop_task.c	sched: Fix migration thread runtime bogosity	2012-10-13 05:39:01 +09:00