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Subject: Re: [PATCH v2] blk-mq: fix null pointer dereference in
 blk_mq_clear_rq_mapping()
To:     Yu Kuai <yukuai1@huaweicloud.com>, axboe@kernel.dk,
        ming.lei@redhat.com, hare@suse.de, john.garry@huawei.com
Cc:     linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        yi.zhang@huawei.com, "yukuai (C)" <yukuai3@huawei.com>
References: <20221011142253.4015966-1-yukuai1@huaweicloud.com>
From:   Yu Kuai <yukuai1@huaweicloud.com>
Message-ID: <c69e005d-7088-c4cd-f584-c4cf5385cdcc@huaweicloud.com>
Date:   Sat, 15 Oct 2022 11:58:41 +0800
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Precedence: bulk

Hi, Jens!

?? 2022/10/11 22:22, Yu Kuai д??:
> From: Yu Kuai <yukuai3@huawei.com>
> 
> Our syzkaller report a null pointer dereference, root cause is
> following:
> 
> __blk_mq_alloc_map_and_rqs
>   set->tags[hctx_idx] = blk_mq_alloc_map_and_rqs
>    blk_mq_alloc_map_and_rqs
>     blk_mq_alloc_rqs
>      // failed due to oom
>      alloc_pages_node
>      // set->tags[hctx_idx] is still NULL
>      blk_mq_free_rqs
>       drv_tags = set->tags[hctx_idx];
>       // null pointer dereference is triggered
>       blk_mq_clear_rq_mapping(drv_tags, ...)
> 
> This is because commit 63064be150e4 ("blk-mq:
> Add blk_mq_alloc_map_and_rqs()") merged the two steps:
> 
> 1) set->tags[hctx_idx] = blk_mq_alloc_rq_map()
> 2) blk_mq_alloc_rqs(..., set->tags[hctx_idx])
> 
> into one step:
> 
> set->tags[hctx_idx] = blk_mq_alloc_map_and_rqs()
> 
> Since tags is not initialized yet in this case, fix the problem by
> checking if tags is NULL pointer in blk_mq_clear_rq_mapping().
> 
> Fixes: 63064be150e4 ("blk-mq: Add blk_mq_alloc_map_and_rqs()")
> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
> Reviewed-by: John Garry <john.garry@huawei.com>
> ---
> Changes in v2:
>   - fix spelling mistakes
>   - add review tag
> 
>   block/blk-mq.c | 7 +++++--
>   1 file changed, 5 insertions(+), 2 deletions(-)
> 
Can you apply this patch?

Thanks,
Kuai

> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 8070b6c10e8d..33292c01875d 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -3112,8 +3112,11 @@ static void blk_mq_clear_rq_mapping(struct blk_mq_tags *drv_tags,
>   	struct page *page;
>   	unsigned long flags;
>   
> -	/* There is no need to clear a driver tags own mapping */
> -	if (drv_tags == tags)
> +	/*
> +	 * There is no need to clear mapping if driver tags is not initialized
> +	 * or the mapping belongs to the driver tags.
> +	 */
> +	if (!drv_tags || drv_tags == tags)
>   		return;
>   
>   	list_for_each_entry(page, &tags->page_list, lru) {
>