CVE-2026-89584 in Linux
Summary
by MITRE • 09/12/2026
In the Linux kernel, the following vulnerability has been resolved:
block: validate user space vectors during extraction
The bio-based drivers don't necessarily check the alignment split, and stacking block drivers don't always handle a misalignment detected after submitting the bio. Validate user vectors against the device's dma_alignment as the bio is built from the iov_iter, rejecting misaligned early with -EINVAL.
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Analysis
by VulDB Data Team • 09/12/2026
The Linux kernel contains a critical input validation flaw within its block layer subsystem that allows for improper handling of memory alignment during direct I/O operations. This vulnerability specifically affects bio-based drivers and stacked block driver architectures where the initial construction of bios from user-space iterators lacks sufficient checks against device-specific DMA alignment requirements. When applications perform direct I/O, they pass vectors to the kernel via iov_iter structures which are then converted into bios for processing by storage devices. The core issue arises because certain bio-based drivers do not verify that the memory buffers provided by userspace meet the strict alignment constraints required by the underlying hardware's Direct Memory Access controller. Furthermore, stacked block drivers often fail to correctly handle or reject misalignments detected after a bio has already been submitted for processing rather than during its initial construction phase.
This lack of early validation creates a scenario where misaligned memory addresses can propagate through the I/O stack without triggering an appropriate error condition at the earliest possible stage. In many hardware configurations, DMA engines require data buffers to be aligned to specific boundaries such as cache line sizes or device page boundaries. If these alignment constraints are violated, it can lead to unpredictable behavior ranging from silent data corruption and performance degradation due to inefficient memory access patterns to severe system instability including kernel panics or crashes when the hardware attempts to perform direct transfers with improperly aligned addresses. The vulnerability essentially represents a failure in input validation where user-supplied parameters are not rigorously checked against device capabilities before being committed to lower-level subsystems that assume valid alignment.
From an operational impact perspective, this flaw can be exploited by local users who have permission to open block devices and perform direct I/O operations. An attacker could craft specific io vectors with deliberately misaligned memory addresses to trigger the vulnerability. Depending on the hardware implementation and kernel configuration, successful exploitation might result in denial of service through system crashes or potential data integrity issues if partial writes occur without proper error handling. While remote code execution is unlikely given that this involves local block device interactions, the reliability and stability impacts are significant for systems relying on high-performance direct I/O workloads such as database servers or virtualization hosts where bio-based drivers are heavily utilized.
The remediation strategy implemented in the kernel update addresses this issue by enforcing strict validation of user space vectors against the device's dma_alignment parameter during the bio construction phase. By rejecting misaligned requests early with an -EINVAL error code, the system prevents invalid memory operations from reaching lower-level driver layers that may not be equipped to handle such errors gracefully. This approach aligns with security best practices emphasizing fail-secure design principles where input validation occurs as close to the trust boundary as possible. The fix ensures that only properly aligned buffers are processed by bio-based drivers, thereby eliminating the risk associated with unhandled alignment mismatches in stacked block driver environments.
This vulnerability maps directly to CWE-20 Improper Input Validation within the Common Weakness Enumeration framework because it involves a failure to verify that user-supplied data meets expected structural constraints before processing. Additionally, from an adversary perspective related to MITRE ATT&CK techniques, this flaw could potentially facilitate Local Privilege Escalation if combined with other vulnerabilities or lead to Denial of Service through resource exhaustion via repeated crash-inducing attempts. Security practitioners should ensure systems are updated to include the patched block layer code which implements these rigorous alignment checks. Administrators managing environments with high I/O throughput requirements should verify that their storage drivers and kernel versions reflect this fix to maintain system stability and prevent potential exploitation through malformed direct I/O requests.