CVE-2026-93154 in Linux
Summary
by MITRE • 09/18/2026
In the Linux kernel, the following vulnerability has been resolved:
RDMA/irdma: Add refcounting to user ring MRs
Prevent userspace from deregistering the MRs that back QP/CQ/SRQ rings by bumping the MR's refcount upon association.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 09/18/2026
The Linux kernel’s RDMA (Remote Direct Memory Access) subsystem, specifically within the Intel irdma driver implementation, addresses a critical resource management flaw related to memory registration lifecycle handling. In high-performance computing and data center environments, RDMA allows applications to bypass the CPU for direct data transfers between application memory and network interface cards. This process relies on Memory Regions (MRs), which are kernel-managed structures that describe contiguous blocks of user-space virtual address space mapped into physical memory. These MRs serve as the foundational abstraction layer enabling hardware access to specific buffers, including those backing Queue Pairs (QPs), Completion Queues (CQs), and Send/Receive Work Queue Rings (SRQs). The vulnerability stems from an incomplete reference counting mechanism for user-space registered MRs that are actively associated with these communication structures.
Prior to the resolution of this issue, when a userspace application mapped memory regions to back QP or CQ rings, the kernel did not sufficiently increment the reference count on those underlying Memory Regions during the association phase. This oversight created a race condition where an application could deregister or unmap its user-space buffers while they were still actively referenced by active RDMA hardware contexts. Because the kernel’s internal data structures retained pointers to these memory regions for ongoing operations, such as sending packets or processing completions, the premature release of the underlying physical pages led to use-after-free conditions. This represents a classic instance of CWE-416, Use After Free, where software continues to use memory that has been freed, potentially leading to arbitrary code execution if an attacker can control the contents of the reallocated memory or cause a denial of service through kernel panic.
The operational impact of this vulnerability is severe for systems relying on RDMA connectivity. An unprivileged local user with access to the relevant device files could trigger the deregistration sequence while hardware operations are pending, causing immediate instability in the kernel space. This can result in system crashes, data corruption within network buffers, or potentially allow a malicious actor to escalate privileges by exploiting the corrupted memory state during subsequent allocations. In cloud and virtualized environments, this flaw compromises the isolation guarantees provided by the hypervisor layer if RDMA passthrough is utilized for guest VMs, as a compromised guest could destabilize the host kernel through similar mechanisms involving shared or passed-through hardware contexts.
The mitigation implemented involves rigorous enforcement of reference counting semantics within the irdma driver’s resource management logic. By bumping the MR's refcount upon association with QP, CQ, and SRQ rings, the kernel ensures that these memory regions remain valid for as long as they are actively used by hardware or pending software operations. This change aligns with standard practices in systems programming where resources must be kept alive until all references to them are explicitly released. The fix prevents premature deallocation of physical pages backing user-space buffers, thereby eliminating the window of vulnerability associated with race conditions between userspace deregistration and kernel-side hardware access.
From a defense-in-depth perspective, this update reinforces adherence to secure coding principles regarding resource lifecycle management. It mitigates risks categorized under CWE-401, Missing Release of Memory after Effective Lifetime, by ensuring that memory is not released while still in active use. Furthermore, it addresses potential exploitation vectors associated with ATT&CK technique T1059, Command and Scripting Interpreter, if the vulnerability were leveraged to execute arbitrary code via kernel exploits. System administrators should ensure that kernels are updated to include this patch, particularly on systems running Intel-based RDMA adapters where userspace applications interact directly with hardware queues. Regular auditing of application behavior regarding memory registration and deregistration patterns can also help identify potential misuse or exploitation attempts in production environments.