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Subject: Re: [PATCH] blktrace: Fix uaf in blk_trace access after removing by
 sysfs
To:     Christoph Hellwig <hch@infradead.org>
CC:     <axboe@kernel.dk>, <rostedt@goodmis.org>, <mingo@redhat.com>,
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References: <20210910092120.182270-1-chengzhihao1@huawei.com>
 <YUq9X2dHG+LkMvQ6@infradead.org>
From:   Zhihao Cheng <chengzhihao1@huawei.com>
Message-ID: <94c819d1-4c3d-fb8d-c32c-c09c84a6108f@huawei.com>
Date:   Thu, 23 Sep 2021 21:39:27 +0800
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在 2021/9/22 13:21, Christoph Hellwig 写道:
Hi Christoph,
> On Fri, Sep 10, 2021 at 05:21:20PM +0800, Zhihao Cheng wrote:
>> +		else {
>> +			/*
>> +			 * Don't remove blk_trace under running state, in
>> +			 * case triggering use-after-free in function
>> +			 * __blk_add_trace().
>> +			 */
>> +			if (bt->trace_state != Blktrace_running)
>> +				ret = blk_trace_remove_queue(q);
>> +			else
>> +				ret = -EBUSY;
>> +		}
>>   		goto out_unlock_bdev;
> So who is going to eventually call blk_trace_free in this case?
Agree. How about removing blk_trace from running_list and stopping it 
before calling blk_trace_free()?
>
> Also Having the check in blk_trace_remove_queue would seem a little
> cleaner.
Oh right, will move the check in v2.