Re: [PATCH v3] md/raid5: reject raid4/5 arrays with too few disks

["yu kuai" <yukuai@fygo.io>]

Hi,

在 2026/9/11 12:27, sashiko-bot@kernel.org 写道:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
>
> Pre-existing issues:
> - [High] Division by zero in `raid5_run()` when assembling an array with an active reshape and insufficient data disks.
> --
>
> commit e2bb0701d8414cbf17eed6287965f8022ffe5eab
> Author: Chen Cheng <chencheng@fnnas.com>
>
> md/raid5: reject raid4/5 arrays with too few disks
>
> raid4 and raid5 require at least two disks, while raid6 requires at least
> four disks. setup_conf() only rejects raid6 arrays with fewer than four
> disks. As a result, an invalid raid4 or raid5 array can be assembled with
> no data disks and later reach raid5_set_limits().
>
> Reported-by: syzbot+de94ddbfff0c9e6fe030@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/r/6a778c82.01d0871a.3a0d52.006a.GAE@google.com/
> Fixes: f63f17350e53 ("md/raid5: use the atomic queue limit update APIs")
>
>> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
>> index b91545ce090de..e1f20035703ba 100644
>> --- a/drivers/md/raid5.c
>> +++ b/drivers/md/raid5.c
>> @@ -7657,9 +7657,11 @@ static struct r5conf *setup_conf(struct mddev *mddev)
>>   			mdname(mddev), mddev->new_layout);
>>   		return ERR_PTR(-EIO);
>>   	}
>> -	if (mddev->new_level == 6 && mddev->raid_disks < 4) {
>> -		pr_warn("md/raid:%s: not enough configured devices (%d, minimum 4)\n",
>> -			mdname(mddev), mddev->raid_disks);
>> +	if ((mddev->new_level != 6 && mddev->raid_disks < 2) ||
>> +	    (mddev->new_level == 6 && mddev->raid_disks < 4)) {
>> +		pr_warn("md/raid:%s: not enough configured devices (%d, minimum %d)\n",
>> +			mdname(mddev), mddev->raid_disks,
>> +			mddev->new_level == 6 ? 4 : 2);
> [Severity: High]
> This isn't a bug introduced by this patch, but does this fully prevent
> invalid array geometries from causing panics during array assembly?
>
> In raid5_run(), if there is an active reshape and the array is assembled with
> insufficient data disks, we calculate new_data_disks and divide by it before
> setup_conf() is called to validate the array geometry:
>
> drivers/md/raid5.c:raid5_run() {
>      if (mddev->reshape_position != MaxSector) {
>          ...
>          new_data_disks = mddev->raid_disks - max_degraded;
>          if (sector_div(here_new, chunk_sectors * new_data_disks)) {
>              ...
>          }
>          ...
>          sector_div(here_old, chunk_sectors * (old_disks-max_degraded));
>      }
>      ...
>      if (mddev->private == NULL)
>          conf = setup_conf(mddev);
> }
This looks like a valid problem as well.
>
> If a crafted superblock sets raid_disks <= max_degraded and reshape_position
> is not MaxSector, these divisions by zero are reached before the new checks
> in setup_conf() can reject the array.
>
> Could these checks be moved earlier in the assembly path to prevent the
> divide-by-zero panics?
>
>>   		return ERR_PTR(-EINVAL);
>>   	}
>>
-- 
Thanks,
Kuai