CVE-2026-97613 in Linux
Summary
by MITRE • 09/25/2026
In the Linux kernel, the following vulnerability has been resolved:
net: mana: Reserve extra CQ slot for the fence completion CQE
The RX completion queue is sized to hold exactly one CQE per posted RX WQE. MANA_FENCE_RQ makes hardware post an additional CQE_RX_OBJECT_FENCE after the packet CQEs. The current sizing reserves no extra slot for it and in rare cases, CQ has no guaranteed slot for the fence CQE when it is full of packet CQEs. This can lead to dropping the fence completion while the driver waits holding RTNL lock throughout the timeout duration. Reserve one extra CQE slot for CQE_RX_OBJECT_FENCE. mana_gd_alloc_memory() requires queue_size to be a power-of-two and at least MANA_PAGE_SIZE; the reservation pushes cq_size past a power-of-two, so round up the CQ size in mana_create_rxq().
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Analysis
by VulDB Data Team • 09/25/2026
The Linux kernel networking subsystem for Microsoft Azure Network Adapter (MANA) drivers contains a resource allocation flaw within the receive completion queue management logic. This vulnerability stems from an incorrect sizing calculation that fails to account for hardware-generated fence completions, leading to potential denial of service conditions under specific high-load scenarios. The MANA driver utilizes a Receive Queue mechanism where software posts Work Queue Elements (WQE) and expects corresponding Completion Queue Entries (CQEs) in return upon packet processing completion. To ensure proper ordering and synchronization between the host and the hardware accelerator, the driver employs a feature known as MANA_FENCE_RQ. This feature instructs the hardware to append an additional CQE of type CQE_RX_OBJECT_FENCE after all standard packet-related CQEs for a given batch of work requests.
The technical flaw lies in the initial reservation of queue slots during the creation of the receive completion queue. The driver calculates the required size based solely on the number of posted RX WQEs, assuming a one-to-one mapping between submitted packets and returned completions. However, because MANA_FENCE_RQ mandates an extra fence CQE per batch or context, the actual consumption rate exceeds the reserved capacity when the queue is near full utilization. In rare cases where the completion queue becomes completely filled with packet CQEs before the driver can poll for new entries, there are no remaining slots available to accept the mandatory fence CQE. This mismatch between expected and required buffer space constitutes a classic resource exhaustion vulnerability within the kernel's network interface layer.
The operational impact of this flaw is significant due to its effect on system stability and lock contention. When the completion queue lacks an available slot for the fence CQE, the hardware cannot signal that previous operations are complete in the ordered manner expected by the driver. Consequently, the MANA driver enters a waiting state, holding the RTNL (Routing Netlink) lock throughout the timeout duration while polling for the missing completion event. The RTNL lock is a global mutex used to protect network configuration changes and interface states across the entire system. Holding this critical lock for an extended period due to a hardware synchronization stall effectively blocks other network operations, including interface configuration, routing table updates, and potentially new packet processing on other interfaces depending on implementation details. This results in a localized denial of service that can degrade or halt broader networking functionality within the affected Linux instance.
From a classification perspective, this vulnerability aligns with CWE-120 Buffer Overflow without bounds check if viewed through the lens of queue capacity management, though it is more accurately described as CWE-400 Resource Exhaustion due to incorrect resource allocation logic. The failure to reserve adequate space for mandatory hardware-generated events leads to a deadlock-like state in the driver's polling loop. In terms of attack vectors and tactical behavior, this scenario relates to ATT&CK technique T1529 System Shutdown or Reboot if the timeout eventually forces a crash or hang that requires manual intervention, although it primarily manifests as service degradation rather than immediate system failure. The root cause is not an exploitable buffer overflow in memory but rather a logical error in queue sizing parameters passed to the hardware initialization routines.
Mitigation strategies focus on correcting the resource allocation logic within the driver source code. As resolved in recent kernel updates, the fix involves modifying mana_create_rxq() to round up the completion queue size to ensure it remains a power-of-two while simultaneously reserving one extra slot specifically for the fence CQE. The underlying memory allocation function mana_gd_alloc_memory imposes constraints requiring queue sizes to be powers of two and at least MANA_PAGE_SIZE in magnitude, necessitating careful rounding calculations to satisfy both hardware requirements and functional needs. Administrators should ensure their systems are updated with kernel versions that include this patch. For environments where immediate patching is not feasible, monitoring for high CPU usage associated with network interface drivers or timeouts in RTNL lock acquisition can serve as an indicator of compromise or active exploitation attempts aimed at triggering the stall condition through sustained high-throughput traffic patterns designed to fill the completion queue rapidly.