Re: [PATCH V2] sched/numa: Fix use-after-free bug in the task_numa_compare

From: Peter Zijlstra
Date: Mon Jan 18 2016 - 12:13:38 EST

On Mon, Jan 18, 2016 at 11:24:21PM +0800, gavin.guo@xxxxxxxxxxxxx wrote:
> From: Gavin Guo <gavin.guo@xxxxxxxxxxxxx>
> The following message can be observed on the Ubuntu v3.13.0-65 with KASan
> backported:


> As commit 1effd9f19324 ("sched/numa: Fix unsafe get_task_struct() in
> task_numa_assign()") points out, the rcu_read_lock() cannot protect the
> task_struct from being freed in the finish_task_switch(). And the bug
> happens in the process of calculation of imp which requires the access of
> p->numa_faults being freed in the following path:
> do_exit()
> current->flags |= PF_EXITING;
> release_task()
> ~~delayed_put_task_struct()~~
> schedule()
> ...
> ...
> rq->curr = next;
> context_switch()
> finish_task_switch()
> put_task_struct()
> __put_task_struct()
> task_numa_free()
> The fix here to get_task_struct() early before end of dst_rq->lock to
> protect the calculation process and also put_task_struct() in the
> corresponding point if finally the dst_rq->curr somehow cannot be
> assigned.
> v1->v2:
> - Fix coding style suggested by Peter Zijlstra.
> Signed-off-by: Gavin Guo <gavin.guo@xxxxxxxxxxxxx>
> Signed-off-by: Liang Chen <liangchen.linux@xxxxxxxxx>

Argh, sorry for not noticing before; this SoB chain is not valid.

Gavin wrote (per From) and send me the patch (per actual email headers),
so Liang never touched it.

Should that be a reviewed-by for him?