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Message-ID: <b7d7b9f9-51f1-5ee4-db38-86afff3a8352@huaweicloud.com>
Date:   Sat, 27 May 2023 09:28:42 +0800
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Subject: Re: [PATCH v2 1/4] md/raid10: fix null-ptr-deref of mreplace in
 raid10_sync_request
To:     Song Liu <song@kernel.org>, linan666@huaweicloud.com
Cc:     bingjingc@synology.com, allenpeng@synology.com,
        alexwu@synology.com, shli@fb.com, neilb@suse.de,
        linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org,
        yukuai3@huawei.com, yi.zhang@huawei.com, houtao1@huawei.com,
        yangerkun@huawei.com
References: <20230526074551.669792-1-linan666@huaweicloud.com>
 <20230526074551.669792-2-linan666@huaweicloud.com>
 <CAPhsuW5ThXyAL2rAyWZC31etY27fqsG+eFHcHtzfCS9Da4bosw@mail.gmail.com>
From:   Li Nan <linan666@huaweicloud.com>
In-Reply-To: <CAPhsuW5ThXyAL2rAyWZC31etY27fqsG+eFHcHtzfCS9Da4bosw@mail.gmail.com>
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在 2023/5/27 5:38, Song Liu 写道:
> On Fri, May 26, 2023 at 12:47 AM <linan666@huaweicloud.com> wrote:
>>
>> From: Li Nan <linan122@huawei.com>
>>
>> need_replace will be set to 1 if no-Faulty mreplace exists, and mreplace
>> will be deref later. However, the latter check of mreplace might set
>> mreplace to NULL, null-ptr-deref occurs if need_replace is 1 at this time.
>>
>> Fix it by merging two checks into one. And replace 'need_replace' with
>> 'mreplace' because their values are always the same.
>>
>> Fixes: ee37d7314a32 ("md/raid10: Fix raid10 replace hang when new added disk faulty")
>> Signed-off-by: Li Nan <linan122@huawei.com>
>> ---
>>   drivers/md/raid10.c | 13 +++++--------
>>   1 file changed, 5 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
>> index 4fcfcb350d2b..e21502c03b45 100644
>> --- a/drivers/md/raid10.c
>> +++ b/drivers/md/raid10.c
>> @@ -3438,7 +3438,6 @@ static sector_t raid10_sync_request(struct mddev *mddev, sector_t sector_nr,
>>                          int must_sync;
>>                          int any_working;
>>                          int need_recover = 0;
>> -                       int need_replace = 0;
>>                          struct raid10_info *mirror = &conf->mirrors[i];
>>                          struct md_rdev *mrdev, *mreplace;
>>
>> @@ -3451,10 +3450,10 @@ static sector_t raid10_sync_request(struct mddev *mddev, sector_t sector_nr,
>>                              !test_bit(In_sync, &mrdev->flags))
>>                                  need_recover = 1;
>>                          if (mreplace != NULL &&
>> -                           !test_bit(Faulty, &mreplace->flags))
>> -                               need_replace = 1;
>> +                           test_bit(Faulty, &mreplace->flags))
>> +                               mreplace = NULL;
>>
>> -                       if (!need_recover && !need_replace) {
>> +                       if (!need_recover && !mreplace) {
>>                                  rcu_read_unlock();
>>                                  continue;
>>                          }
>> @@ -3470,8 +3469,6 @@ static sector_t raid10_sync_request(struct mddev *mddev, sector_t sector_nr,
>>                                  rcu_read_unlock();
>>                                  continue;
>>                          }
> 
> To make sure I understand the issue correctly:
> 
> The null-ptr-deref only happens when the Faulty bit was set after the
> last check and before this check below, right?
> 

Yes. I will improve log in next version.

-- 
Thanks,
Nan