dm: limit swapping tables for devices with zone write plugs

Overview

In the Linux kernel, the following vulnerability has been resolved:

dm: limit swapping tables for devices with zone write plugs

dm_revalidate_zones() only allowed new or previously unzoned devices to call blk_revalidate_disk_zones(). If the device was already zoned, disk->nr_zones would always equal md->nr_zones, so dm_revalidate_zones() returned without doing any work. This would make the zoned settings for the device not match the new table. If the device had zone write plug resources, it could run into errors like bdev_zone_is_seq() reading invalid memory because disk->conv_zones_bitmap was the wrong size.

If the device doesn't have any zone write plug resources, calling blk_revalidate_disk_zones() will always correctly update device. If blk_revalidate_disk_zones() fails, it can still overwrite or clear the current disk->nr_zones value. In this case, DM must restore the previous value of disk->nr_zones, so that the zoned settings will continue to match the previous value that it fell back to.

If the device already has zone write plug resources, blk_revalidate_disk_zones() will not correctly update them, if it is called for arbitrary zoned device changes. Since there is not much need for this ability, the easiest solution is to disallow any table reloads that change the zoned settings, for devices that already have zone plug resources. Specifically, if a device already has zone plug resources allocated, it can only switch to another zoned table that also emulates zone append. Also, it cannot change the device size or the zone size. A device can switch to an error target.

Affected

• Linux >= bb37d77239af25cde59693dbe3fac04dd17d7b29 < 13c0425c99c67c2296f1eec61254a4f91484eac3
• Linux >= bb37d77239af25cde59693dbe3fac04dd17d7b29 < ac8acb0bfd98a1c65f3ca9a3e217a766124eebd8
• Linux >= bb37d77239af25cde59693dbe3fac04dd17d7b29 < 121218bef4c1df165181f5cd8fc3a2246bac817e
• Linux 5.14

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.