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SubjectRe: [PATCH] block: Fix use-after-free issue accessing struct io_cq
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On 3/11/20 4:37 AM, Sahitya Tummala wrote:
> There is a potential race between ioc_release_fn() and
> ioc_clear_queue() as shown below, due to which below kernel
> crash is observed. It also can result into use-after-free
> issue.
>
> context#1: context#2:
> ioc_release_fn() __ioc_clear_queue() gets the same icq
> ->spin_lock(&ioc->lock); ->spin_lock(&ioc->lock);
> ->ioc_destroy_icq(icq);
> ->list_del_init(&icq->q_node);
> ->call_rcu(&icq->__rcu_head,
> icq_free_icq_rcu);
> ->spin_unlock(&ioc->lock);
> ->ioc_destroy_icq(icq);
> ->hlist_del_init(&icq->ioc_node);
> This results into below crash as this memory
> is now used by icq->__rcu_head in context#1.
> There is a chance that icq could be free'd
> as well.
>
> 22150.386550: <6> Unable to handle kernel write to read-only memory
> at virtual address ffffffaa8d31ca50

Fix looks good to me, applied.

--
Jens Axboe

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