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Subject: Re: [PATCH 1/3] md/raid10: fix null-ptr-deref of mreplace in
 raid10_sync_request
To:     linan666@huaweicloud.com, song@kernel.org, shli@fb.com,
        allenpeng@synology.com, alexwu@synology.com,
        bingjingc@synology.com, neilb@suse.de
Cc:     linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org,
        linan122@huawei.com, yi.zhang@huawei.com, houtao1@huawei.com,
        yangerkun@huawei.com, "yukuai (C)" <yukuai3@huawei.com>
References: <20230522115449.2203939-1-linan666@huaweicloud.com>
 <20230522115449.2203939-2-linan666@huaweicloud.com>
From:   Yu Kuai <yukuai1@huaweicloud.com>
Message-ID: <6c2d40de-7b8c-d84d-d9a2-7c5dce7471aa@huaweicloud.com>
Date:   Mon, 22 May 2023 21:01:05 +0800
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Hi,

?? 2023/05/22 19:54, linan666@huaweicloud.com д??:
> 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;

need_recover can be removed as well. Otherwise, this patch looks good to
me.

Thanks,
Kuai
> -			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;
>   			}
> -			if (mreplace && test_bit(Faulty, &mreplace->flags))
> -				mreplace = NULL;
>   			/* Unless we are doing a full sync, or a replacement
>   			 * we only need to recover the block if it is set in
>   			 * the bitmap
> @@ -3594,11 +3591,11 @@ static sector_t raid10_sync_request(struct mddev *mddev, sector_t sector_nr,
>   				bio = r10_bio->devs[1].repl_bio;
>   				if (bio)
>   					bio->bi_end_io = NULL;
> -				/* Note: if need_replace, then bio
> +				/* Note: if replace is not NULL, then bio
>   				 * cannot be NULL as r10buf_pool_alloc will
>   				 * have allocated it.
>   				 */
> -				if (!need_replace)
> +				if (!mreplace)
>   					break;
>   				bio->bi_next = biolist;
>   				biolist = bio;
>