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cgroup: css_task_iter_skip()'d iterators must be advanced before accessed

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b636fd38dc ("cgroup: Implement css_task_iter_skip()") introduced
css_task_iter_skip() which is used to fix task iterations skipping
dying threadgroup leaders with live threads.  Skipping is implemented
as a subportion of full advancing but css_task_iter_next() forgot to
fully advance a skipped iterator before determining the next task to
visit causing it to return invalid task pointers.

Fix it by making css_task_iter_next() fully advance the iterator if it
has been skipped since the previous iteration.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: syzbot
Link: http://lkml.kernel.org/r/00000000000097025d058a7fd785@google.com
Fixes: b636fd38dc ("cgroup: Implement css_task_iter_skip()")
This commit is contained in:
Tejun Heo 2019-06-05 09:54:34 -07:00
parent c03cd7738a
commit cee0c33c54
1 changed files with 4 additions and 0 deletions
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4
kernel/cgroup/cgroup.c
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@ -4550,6 +4550,10 @@ struct task_struct *css_task_iter_next(struct css_task_iter *it)
spin_lock_irq(&css_set_lock);
/* @it may be half-advanced by skips, finish advancing */
if (it->flags & CSS_TASK_ITER_SKIPPED)
css_task_iter_advance(it);
if (it->task_pos) {
it->cur_task = list_entry(it->task_pos, struct task_struct,
cg_list);