CVE-2025-39791
NoneCVSS
—
EPSS
0.1%
Published
Sep 11, 2025
CISA due date
—
Cloudanix analysis
A bug in Linux encrypted storage handling for certain modern disk drives can freeze the system or silently corrupt data written to disk.
- Exploitation
- Local Privilege
- Attacker needs
- Local User
- Complexity
- Moderate
- Impact
- Data Tampering
- Component
- OS kernel
- Class
- Race Condition
- Remediation
- Upgrade
- Effort
- Medium
- Patch risk
- Low
What it actually does
In dm-crypt with zoned targets, BIO splitting via max_write_size triggers deadlock during blk_queue_enter under queue freeze and returns incorrect written sectors for zone append operations, corrupting xfs or btrfs metadata.
Why it matters to the business
Linux systems using dm-crypt on zoned block devices face risk of kernel deadlocks causing system hangs and file system data corruption leading to downtime and potential data loss; the issue affects downstream Linux distributions and storage stacks with zoned hardware.
How an attack unfolds
An attacker or workload issues large sequential writes exceeding dm-crypt max_write_size to a zoned dm-crypt target; the resulting split BIOs cause either repeated blk_queue_enter blocking that deadlocks with queue freeze or chained regular writes that return wrong sector values, corrupting file system structures.
How to fix it
Upgrade the Linux kernel to a version containing commit 8864616719b6bbf92356bc89ff544b0cd484c656 or later; this sets max_hw_sectors appropriately and prevents partial BIO acceptance in crypt_map for zoned targets.
How to confirm the fix worked
Verify the running kernel contains commit 8864616719b6bbf92356bc89ff544b0cd484c656; confirm get_max_request_sectors returns full BIO size and that dm-crypt max_hw_sectors is capped at BIO_MAX_VECS << PAGE_SECTORS_SHIFT; test large writes on zoned dm-crypt devices without observing deadlock or corruption.
Typical attack path
- Identify or configure a dm-crypt target backed by zoned block device
- Issue large write or zone-append BIOs larger than max_write_size
- Trigger dm-crypt internal splitting and zone write plugging
- Initiate or wait for queue freeze operation to induce deadlock or observe sector misreporting
- Continue I/O to trigger file system corruption in xfs or btrfs
How to detect it
Review kernel logs for dm-crypt zone write plug deadlocks, blk_queue_enter stalls, or xfs/btrfs corruption warnings after large writes; inspect dm-crypt device mapper tables and zoned device usage via /sys/block; correlate with workloads issuing large sequential writes.
What your security team should do
- Prioritize kernel updates containing 8864616719b6bbf92356bc89ff544b0cd484c656 on all systems using dm-crypt with zoned storage
- Audit dm-crypt configurations for zoned devices and consider temporary max_write_size reduction if patching is delayed
- Monitor for kernel hangs or xfs/btrfs errors on affected hosts until remediated
The record
In the Linux kernel, the following vulnerability has been resolved: dm: dm-crypt: Do not partially accept write BIOs with zoned targets Read and write operations issued to a dm-crypt target may be split according to the dm-crypt internal limits defined by the max_read_size and max_write_size module parameters (default is 128 KB). The intent is to improve processing time of large BIOs by splitting them into smaller operations that can be parallelized on different CPUs. For zoned dm-crypt targets, this BIO splitting is still done but without the parallel execution to ensure that the issuing order of write operations to the underlying devices remains sequential. However, the splitting itself causes other problems: 1) Since dm-crypt relies on the block layer zone write plugging to handle zone append emulation using regular write operations, the reminder of a split write BIO will always be plugged into the target zone write plugged. Once the on-going write BIO finishes, this reminder BIO is unplugged and issued from the zone write plug work. If this reminder BIO itself needs to be split, the reminder will be re-issued and plugged again, but that causes a call to a blk_queue_enter(), which may block if a queue freeze operation was initiated. This results in a deadlock as DM submission still holds BIOs that the queue freeze side is waiting for. 2) dm-crypt relies on the emulation done by the block layer using regular write operations for processing zone append operations. This still requires to properly return the written sector as the BIO sector of the original BIO. However, this can be done correctly only and only if there is a single clone BIO used for processing the original zone append operation issued by the user. If the size of a zone append operation is larger than dm-crypt max_write_size, then the orginal BIO will be split and processed as a chain of regular write operations. Such chaining result in an incorrect written sector being returned to the zone append issuer using the original BIO sector. This in turn results in file system data corruptions using xfs or btrfs. Fix this by modifying get_max_request_size() to always return the size of the BIO to avoid it being split with dm_accpet_partial_bio() in crypt_map(). get_max_request_size() is renamed to get_max_request_sectors() to clarify the unit of the value returned and its interface is changed to take a struct dm_target pointer and a pointer to the struct bio being processed. In addition to this change, to ensure that crypt_alloc_buffer() works correctly, set the dm-crypt device max_hw_sectors limit to be at most BIO_MAX_VECS << PAGE_SECTORS_SHIFT (1 MB with a 4KB page architecture). This forces DM core to split write BIOs before passing them to crypt_map(), and thus guaranteeing that dm-crypt can always accept an entire write BIO without needing to split it. This change does not have any effect on the read path of dm-crypt. Read operations can still be split and the BIO fragments processed in parallel. There is also no impact on the performance of the write path given that all zone write BIOs were already processed inline instead of in parallel. This change also does not affect in any way regular dm-crypt block devices.
Affected packages
| Ecosystem | Package | Introduced | Fixed |
|---|---|---|---|
| Debian:13 | linux | 0 | No fix |
| Debian:14 | linux | 0 | No fix |
| Debian:14 | linux | 0 | 6.16.5-1 |
| Linux | Kernel | 6.10.0 | 6.12.44 |
| openSUSE:Leap 16.0 | dtb-aarch64 | 0 | 6.12.0-160000.6.1 |
| openSUSE:Leap 16.0 | kernel-64kb | 0 | 6.12.0-160000.6.1 |
| openSUSE:Leap 16.0 | kernel-default | 0 | 6.12.0-160000.6.1 |
| openSUSE:Leap 16.0 | kernel-default-base | 0 | 6.12.0-160000.6.1.160000.2.4 |
| openSUSE:Leap 16.0 | kernel-docs | 0 | 6.12.0-160000.6.1 |
| openSUSE:Leap 16.0 | kernel-kvmsmall | 0 | 6.12.0-160000.6.1 |
| openSUSE:Leap 16.0 | kernel-obs-build | 0 | 6.12.0-160000.6.1 |
| openSUSE:Leap 16.0 | kernel-obs-qa | 0 | 6.12.0-160000.6.1 |
| openSUSE:Leap 16.0 | kernel-rt | 0 | 6.12.0-160000.6.1 |
| openSUSE:Leap 16.0 | kernel-source | 0 | 6.12.0-160000.6.1 |
| openSUSE:Leap 16.0 | kernel-syms | 0 | 6.12.0-160000.6.1 |
| openSUSE:Leap 16.0 | kernel-zfcpdump | 0 | 6.12.0-160000.6.1 |
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