sched, cgroup: Use exit hook to avoid use-after-free crash (068c5cc5) · Commits · 戴 / test

By not notifying the controller of the on-exit move back to init_css_set, we fail to move the task out of the previous cgroup's cfs_rq. This leads to an opportunity for a cgroup-destroy to come in and free the cgroup (there are no active tasks left in it after all) to which the not-quite dead task is still enqueued. Reported-by:

Miklos Vajna <vmiklos@frugalware.org> Fixed-by:

Mike Galbraith <efault@gmx.de> Signed-off-by:

Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: <stable@kernel.org> Cc: Mike Galbraith <efault@gmx.de> Signed-off-by:

Ingo Molnar <mingo@elte.hu> LKML-Reference: <1293206353.29444.205.camel@laptop>

kernel/sched.c

+18 −0

Original line number	Diff line number	Diff line
		@@ -606,6 +606,9 @@ static inline struct task_group task_group(struct task_struct p)
		struct task_group *tg;
		struct cgroup_subsys_state *css;

		if (p->flags & PF_EXITING)
		return &root_task_group;

		css = task_subsys_state_check(p, cpu_cgroup_subsys_id,
		lockdep_is_held(&task_rq(p)->lock));
		tg = container_of(css, struct task_group, css);
		@@ -8880,6 +8883,20 @@ cpu_cgroup_attach(struct cgroup_subsys ss, struct cgroup cgrp,
		}
		}

		static void
		cpu_cgroup_exit(struct cgroup_subsys ss, struct task_struct task)
		{
		/*
		* cgroup_exit() is called in the copy_process() failure path.
		* Ignore this case since the task hasn't ran yet, this avoids
		* trying to poke a half freed task state from generic code.
		*/
		if (!(task->flags & PF_EXITING))
		return;

		sched_move_task(task);
		}

		#ifdef CONFIG_FAIR_GROUP_SCHED
		static int cpu_shares_write_u64(struct cgroup cgrp, struct cftype cftype,
		u64 shareval)
		@@ -8952,6 +8969,7 @@ struct cgroup_subsys cpu_cgroup_subsys = {
		.destroy = cpu_cgroup_destroy,
		.can_attach = cpu_cgroup_can_attach,
		.attach = cpu_cgroup_attach,
		.exit = cpu_cgroup_exit,
		.populate = cpu_cgroup_populate,
		.subsys_id = cpu_cgroup_subsys_id,
		.early_init = 1,

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