linux-kernel - Re: [PATCH] drivers:md:fix a potential use-after-free bug

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Message-ID: <6b4c8938-a8a9-1a14-87bd-f30e4eda2b3d@linux.dev>
Date:   Tue, 17 Aug 2021 15:47:16 +0800
From:   Guoqing Jiang <guoqing.jiang@...ux.dev>
To:     Song Liu <song@...nel.org>, lwt105 <3061522931@...com>
Cc:     linux-raid <linux-raid@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drivers:md:fix a potential use-after-free bug



On 8/14/21 12:16 AM, Song Liu wrote:
> On Thu, Aug 12, 2021 at 8:46 PM lwt105<3061522931@...com>  wrote:
>> In line 2867, "raid5_release_stripe(sh);" drops the reference to sh and
>> may cause sh to be released. However, sh is subsequently used in lines
>> 2869 "if (sh->batch_head && sh != sh->batch_head)". This may result in an
>> use-after-free bug.
>>
>> It can be fixed by moving "raid5_release_stripe(sh);" to the bottom of
>> the function.
>>
>> Signed-off-by: lwt105<3061522931@...com>
> The fix looks reasonable.

I am not sure this is needed unless there is real calltrace to prove it. 
Because raid5_release_stripe
doesn't mean it will release the sh's memory,  pls see the comment 
before clear_batch_ready in
handle_stripe, and the path handle_stripe -> handle_stripe_clean_event 
-> break_stripe_batch_list.

Thanks,
Guoqing