Re: [PATCH 1/3] md/raid0: reject a takeover whose zones cannot cover the array

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [High] md/raid0: raid0_takeover_check() sums member sizes instead of checking zones
- [Medium] md/raid0: raid0_takeover_check() counts inactive devices in coverage
--

commit bf35a10fdad5f2b5f8c0ec6f68f21e7ed3e9a106
Author: Zizhi Wo <wozizhi@huawei.com>

md/raid0: reject a takeover whose zones cannot cover the array

This patch adds raid0_takeover_check() to reject takeovers into raid0 when
the sum of chunk-aligned member sizes is smaller than the capacity
advertised by the gendisk.

> diff --git a/drivers/md/raid0.c b/drivers/md/raid0.c
> index 35e103f0c2c3e..fccc62a5feccd 100644
> --- a/drivers/md/raid0.c
> +++ b/drivers/md/raid0.c
> @@ -643,6 +643,34 @@ static void raid0_error(struct mddev *mddev, struct md_rdev *rdev)
>  	}
>  }
>  
> +/*
> + * Refuse a takeover whose strip zones cannot cover the capacity the gendisk
> + * advertises: raid0 derives those zones from the sizes of its members, so
> + * find_zone() cannot map I/O that falls beyond them.
> + */
> +static int raid0_takeover_check(struct mddev *mddev, int chunk)
> +{
> +	sector_t capacity = get_capacity(mddev->gendisk);
> +	sector_t coverage = 0;
> +	struct md_rdev *rdev;
> +
> +	rdev_for_each(rdev, mddev) {
> +		sector_t sectors = rdev->sectors;
> +
> +		sector_div(sectors, chunk);
> +		coverage += sectors * chunk;
> +	}

[Severity: Medium]
Does rdev_for_each() in raid0_takeover_check() also count faulty or spare
devices that are still attached to mddev->disks with rdev->raid_disk < 0?

When a mirror drive fails in raid1 or raid10, remove_and_add_spares() ->
hot_remove_disk() sets rdev->raid_disk = -1, but the rdev remains in
mddev->disks until unbound (as do spares).

If the active member in a degraded raid1 or raid10 array was imported
without metadata (rdev->sectors == 0) while a failed or spare rdev in
mddev->disks has rdev->sectors >= capacity, raid0_takeover_check() will
count the inactive rdev's sectors and return 0.

Then raid0_takeover_raid1() and raid0_takeover_raid10() will mutate live
mddev state (such as mddev->chunk_sectors, mddev->degraded,
mddev->resync_offset, and mddev->flags) before create_strip_zones() fails,
and level_store() in drivers/md/md.c does not restore those fields on
error.

Should raid0_takeover_check() skip devices with rdev->raid_disk < 0?

> +
> +	if (coverage < capacity) {
> +		pr_warn("md/raid0:%s: refusing takeover, zones cover only %llu of %llu sectors\n",
> +			mdname(mddev), (unsigned long long)coverage,
> +			(unsigned long long)capacity);
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
>  static void *raid0_takeover_raid45(struct mddev *mddev)
>  {
>  	struct md_rdev *rdev;
> @@ -665,6 +693,9 @@ static void *raid0_takeover_raid45(struct mddev *mddev)
>  		rdev->sectors = mddev->dev_sectors;
>  	}
>  
> +	if (raid0_takeover_check(mddev, mddev->chunk_sectors))
> +		return ERR_PTR(-EINVAL);
> +
>  	/* Set new parameters */
>  	mddev->new_level = 0;
>  	mddev->new_layout = 0;
> @@ -707,6 +738,9 @@ static void *raid0_takeover_raid10(struct mddev *mddev)
>  		return ERR_PTR(-EINVAL);
>  	}
>  
> +	if (raid0_takeover_check(mddev, mddev->chunk_sectors))
> +		return ERR_PTR(-EINVAL);

[Severity: High]
Can a larger member mask a zero-sized or undersized member during a
raid10 -> raid0 takeover when raid0_takeover_check() only checks the sum
of rdev->sectors?

Unlike raid0_takeover_raid45(), which assigns rdev->sectors =
mddev->dev_sectors for each device, raid0_takeover_raid10() leaves each
member's rdev->sectors unchanged.

Consider a 4-disk degraded raid10 (near=2) array with 2 active disks where
one active member was imported without metadata (rdev2->sectors == 0) and
the other active member has rdev0->sectors >= capacity (2 * dev_sectors).
raid0_takeover_check() sums rdev->sectors across members, sees
coverage >= capacity, and succeeds.

create_strip_zones() then builds two zones:

drivers/md/raid0.c:create_strip_zones() {
	...
	zone->nb_dev = cnt;
	zone->zone_end = smallest->sectors * cnt;
	...
}

Here strip_zone[0] gets nb_dev = 2, smallest = rdev2 (0), and
zone_end = 0, while strip_zone[1] gets dev_start = 0, nb_dev = 1
(containing only rdev0), and zone_end = capacity. Because
strip_zone[1].nb_dev == 1, create_strip_zones() succeeds even with
default_layout == 0.

On subsequent I/O, find_zone() checks sector < z[i].zone_end, so
strip_zone[0] (with zone_end == 0) is skipped completely and all array I/O
is mapped linearly onto rdev0 alone in strip_zone[1], dropping rdev2 from
the stripe layout and reading/writing past mddev->dev_sectors on rdev0.

Similarly, if there are 3 or more active disks with mismatched
rdev->sectors whose sum is >= capacity, raid0_takeover_check() succeeds
and raid0_takeover_raid10() sets mddev->degraded = 0,
mddev->resync_offset = MaxSector, and clears UNSUPPORTED_MDDEV_FLAGS
before create_strip_zones() fails with -EOPNOTSUPP, leaving the raid10
array with corrupted state.

Should raid0 takeovers require every active member to have enough sectors
(e.g., checking each active member against mddev->dev_sectors, or checking
that a single uniform zone covers capacity)?

[ ... ]

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-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261017005802.2212102-1-wozizhi@huaweicloud.com?part=1