linux-kernel - Re: [PATCH] md/raid5: Convert stripe_head's "dev" to flexible array member

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Date:   Mon, 22 May 2023 19:49:38 +0800
From:   Yu Kuai <yukuai1@...weicloud.com>
To:     Christoph Hellwig <hch@...radead.org>,
        Kees Cook <keescook@...omium.org>
Cc:     Song Liu <song@...nel.org>, linux-raid@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org,
        "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH] md/raid5: Convert stripe_head's "dev" to flexible array
 member

Hi, Christoph

在 2023/05/18 12:27, Christoph Hellwig 写道:

It's not related to this patch, just I think I found a problem while
reviewing raid5 code, commit e82ed3a4fbb5 ("md/raid6: refactor
raid5_read_one_chunk") changes the caculation of 'end_sector',
'end_sector' is compared to 'rdev->recovery_offset', so it should be
offset to rdev, but this commit change it to offset to the array.

Perhaps following change will make sense:

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 7e2bbcfef325..8686d629e3f2 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -5516,7 +5516,7 @@ static int raid5_read_one_chunk(struct mddev 
*mddev, struct bio *raid_bio)

         sector = raid5_compute_sector(conf, raid_bio->bi_iter.bi_sector, 0,
                                       &dd_idx, NULL);
-       end_sector = bio_end_sector(raid_bio);
+       end_sector = sector + bio_sectors(raid_bio);

         rcu_read_lock();
         if (r5c_big_stripe_cached(conf, sector))


Thanks,
Kuai
> On Wed, May 17, 2023 at 04:33:14PM -0700, Kees Cook wrote:
>>   	sc = kmem_cache_create(conf->cache_name[conf->active_name],
>> -			       sizeof(struct stripe_head)+(devs-1)*sizeof(struct r5dev),
>> +			       struct_size((struct stripe_head *)0, dev, devs),
>>   			       0, 0, NULL);
>>   	if (!sc)
>>   		return 1;
>> @@ -2559,7 +2559,7 @@ static int resize_stripes(struct r5conf *conf, int newsize)
>>   
>>   	/* Step 1 */
>>   	sc = kmem_cache_create(conf->cache_name[1-conf->active_name],
>> -			       sizeof(struct stripe_head)+(newsize-1)*sizeof(struct r5dev),
>> +			       struct_size((struct stripe_head *)0, dev, newsize),
> 
> The constant you're casting here should be NULL, not 0.
> Also given that this expression is duplicated, I'd suggest a little
> helper for it…
> 
>> -	} dev[1]; /* allocated with extra space depending of RAID geometry */
>> +	} dev[]; /* allocated with extra space depending of RAID geometry */
> 
> And this isn't extra space over the single entry anymore, so I'd
> change this to:
> 
> 	/* allocated depending of RAID geometry */
> .
>