CVE-2024-55642: Vulnerability in Linux Linux

Severity: highType: vulnerabilityCVE-2024-55642

In the Linux kernel, the following vulnerability has been resolved: block: Prevent potential deadlocks in zone write plug error recovery Zone write plugging for handling writes to zones of a zoned block device always execute a zone report whenever a write BIO to a zone fails. The intent of this is to ensure that the tracking of a zone write pointer is always correct to ensure that the alignment to a zone write pointer of write BIOs can be checked on submission and that we can always correctly emulate zone append operations using regular write BIOs. However, this error recovery scheme introduces a potential deadlock if a device queue freeze is initiated while BIOs are still plugged in a zone write plug and one of these write operation fails. In such case, the disk zone write plug error recovery work is scheduled and executes a report zone. This in turn can result in a request allocation in the underlying driver to issue the report zones command to the device. But with the device queue freeze already started, this allocation will block, preventing the report zone execution and the continuation of the processing of the plugged BIOs. As plugged BIOs hold a queue usage reference, the queue freeze itself will never complete, resulting in a deadlock. Avoid this problem by completely removing from the zone write plugging code the use of report zones operations after a failed write operation, instead relying on the device user to either execute a report zones, reset the zone, finish the zone, or give up writing to the device (which is a fairly common pattern for file systems which degrade to read-only after write failures). This is not an unreasonnable requirement as all well-behaved applications, FSes and device mapper already use report zones to recover from write errors whenever possible by comparing the current position of a zone write pointer with what their assumption about the position is. The changes to remove the automatic error recovery are as follows: - Completely remove the error recovery work and its associated resources (zone write plug list head, disk error list, and disk zone_wplugs_work work struct). This also removes the functions disk_zone_wplug_set_error() and disk_zone_wplug_clear_error(). - Change the BLK_ZONE_WPLUG_ERROR zone write plug flag into BLK_ZONE_WPLUG_NEED_WP_UPDATE. This new flag is set for a zone write plug whenever a write opration targetting the zone of the zone write plug fails. This flag indicates that the zone write pointer offset is not reliable and that it must be updated when the next report zone, reset zone, finish zone or disk revalidation is executed. - Modify blk_zone_write_plug_bio_endio() to set the BLK_ZONE_WPLUG_NEED_WP_UPDATE flag for the target zone of a failed write BIO. - Modify the function disk_zone_wplug_set_wp_offset() to clear this new flag, thus implementing recovery of a correct write pointer offset with the reset (all) zone and finish zone operations. - Modify blkdev_report_zones() to always use the disk_report_zones_cb() callback so that disk_zone_wplug_sync_wp_offset() can be called for any zone marked with the BLK_ZONE_WPLUG_NEED_WP_UPDATE flag. This implements recovery of a correct write pointer offset for zone write plugs marked with BLK_ZONE_WPLUG_NEED_WP_UPDATE and within the range of the report zones operation executed by the user. - Modify blk_revalidate_seq_zone() to call disk_zone_wplug_sync_wp_offset() for all sequential write required zones when a zoned block device is revalidated, thus always resolving any inconsistency between the write pointer offset of zone write plugs and the actual write pointer position of sequential zones.

AI Analysis

Technical Summary

CVE-2024-55642 is a vulnerability identified in the Linux kernel's block device subsystem, specifically related to zoned block devices and their zone write plugging mechanism. Zoned block devices segment storage into zones with write pointers that must be carefully managed to ensure data integrity and correct write alignment. The vulnerability arises from the error recovery process triggered when a write BIO (block I/O operation) to a zone fails. The existing mechanism attempts to recover by issuing a report zones command to update the zone write pointer. However, if a device queue freeze occurs concurrently while BIOs are still plugged, the report zones command allocation blocks due to the freeze, causing a deadlock. This deadlock occurs because the plugged BIOs hold a queue usage reference, preventing the freeze from completing and halting further processing. To mitigate this, the Linux kernel maintainers removed the automatic error recovery involving report zones commands from the zone write plugging code. Instead, they rely on the device user (e.g., file systems or device mappers) to handle error recovery explicitly by issuing report zones, resetting, finishing zones, or ceasing writes upon failure. The patch removes the error recovery work and associated resources, changes the error flag to indicate the need for write pointer updates, and modifies relevant functions to synchronize write pointer offsets during user-initiated recovery operations or device revalidation. This approach prevents the deadlock by avoiding automatic report zones commands during error recovery, delegating responsibility to higher-level components that already implement such recovery patterns. The vulnerability affects Linux kernel versions identified by the commit hash dd291d77cc90eb6a86e9860ba8e6e38eebd57d12 and was published on January 11, 2025. No known exploits are reported in the wild, and no CVSS score has been assigned yet.

Potential Impact

For European organizations, this vulnerability could lead to system hangs or deadlocks in environments using zoned block devices on Linux systems, particularly those employing device queue freezing during error conditions. Zoned block devices are increasingly used in enterprise storage solutions for their performance and capacity benefits, especially in data centers and cloud infrastructure. A deadlock in the block device layer can cause critical storage operations to stall, potentially leading to application downtime, data unavailability, or degraded service performance. This is particularly impactful for sectors relying on high availability and data integrity, such as finance, healthcare, telecommunications, and government services. While the vulnerability does not directly expose confidentiality or integrity risks, the availability impact could disrupt business operations and service delivery. Since the deadlock requires specific conditions (device queue freeze concurrent with write BIO failures), exploitation complexity is moderate, and the scope is limited to systems using zoned block devices with the affected kernel versions. Nonetheless, given Linux's widespread use in European enterprise and cloud environments, the potential for operational disruption is significant if unpatched systems encounter these conditions.

Mitigation Recommendations

European organizations should prioritize updating Linux kernels to versions that include the fix for CVE-2024-55642. Since the patch removes automatic error recovery and relies on higher-level components to manage write pointer updates, organizations should audit their storage stack and file systems to ensure they correctly handle zoned block device error recovery by issuing report zones, resets, or finishing zones as appropriate. Storage administrators should monitor for signs of device queue freezes or write BIO failures and implement alerting to detect potential deadlocks early. Testing storage workloads with zoned block devices under error conditions can help validate recovery procedures. Additionally, organizations should consider isolating critical workloads on storage devices not affected by this vulnerability until patches are applied. For environments using device mapper or advanced file systems, verifying compatibility with the updated kernel behavior is essential to prevent unexpected failures. Finally, maintaining robust backup and disaster recovery plans will mitigate the impact of any availability disruptions caused by this or related storage issues.