CVE-2026-98352 in Linux
Summary
by MITRE • 10/06/2026
In the Linux kernel, the following vulnerability has been resolved:
RDMA/rtrs-clt: Fix CQ pool leak when connect is interrupted
The client borrows shared CQ credits in the ADDR_RESOLVED handler via ib_cq_pool_get(), before the peer is connected. create_cm() can return -ERESTARTSYS from wait_event_interruptible_timeout() without destroying the CM ID. The init_conns() and stop-and-destroy paths then call destroy_con_cq_qp() while cq is still NULL (no PUT) and only afterwards rdma_destroy_id().
CMA serializes the handler against rdma_destroy_id() with handler_mutex, but that does not order the GET against destroy_con_cq_qp(). If ADDR_RESOLVED has already passed the DESTROYING check, it can take con_mutex, GET credits, and then lose the con to kfree. Device unregister later hits WARN_ON(cq->cqe_used) in ib_cq_pool_cleanup().
Set a per-connection flag under con_mutex before CQ/QP teardown so a racing ADDR_RESOLVED cannot borrow credits after teardown has begun.
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Analysis
by VulDB Data Team • 10/06/2026
The Linux kernel vulnerability identified within the RDMA/rtrs-clt subsystem involves a race condition during connection establishment that leads to resource leaks and potential system instability. The core issue stems from an improper synchronization between the address resolution handler and the connection teardown logic. Specifically, when establishing a remote direct memory access connection, the client borrows shared Completion Queue credits using ib_cq_pool_get() within the ADDR_RESOLVED handler before the peer is fully connected. This operation assumes that the connection context will remain valid for the duration of the credit usage. However, if the create_cm function returns -ERESTARTSYS due to a signal interrupting wait_event_interruptible_timeout(), the Connection Manager ID may not be properly destroyed immediately. Consequently, subsequent initialization or termination paths attempt to destroy completion queues and queue pairs via destroy_con_cq_qp() while the connection object is still in an inconsistent state where the CQ pointer remains NULL because no PUT operation has been performed to release previously borrowed credits.
This race condition creates a scenario where device unregistration triggers a warning within ib_cq_pool_cleanup(), specifically WARN_ON(cq->cqe_used), indicating that completion queue entries are being used without proper accounting or cleanup. The underlying technical flaw is a lack of ordering between the GET operation for CQ credits and the destroy_con_cq_qp function. Although the Connection Manager serializes handlers against rdma_destroy_id() using handler_mutex, this mutex does not protect the critical section where credits are borrowed in the ADDR_RESOLVED handler from being accessed after teardown has begun. If the address resolution phase completes past a DESTROYING check before the connection is fully torn down, it can acquire con_mutex and borrow additional credits even as the connection context is about to be freed by kfree. This results in a use-after-free scenario or at minimum a significant resource leak where CQ credits are consumed but never returned to the pool, eventually exhausting available resources for RDMA operations on that device.
From a security and operational impact perspective, this vulnerability falls under CWE-401 Missing Release of Resource after Effective Lifetime, as well as CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization Race Condition. The immediate effect is the degradation of system stability due to resource exhaustion in the RDMA subsystem. Over time, repeated occurrences can lead to denial of service conditions where new connections cannot be established or existing data transfers fail because no CQ credits are available for processing completion events. Furthermore, if an attacker can trigger frequent connection interruptions and teardowns, they could accelerate this resource leak, potentially causing a system-wide performance degradation or crash when the kernel hits critical warnings during device unregistration. This align with ATT&CK technique T1496 Resource Hijacking, specifically in the context of exhausting computational resources to disrupt service availability.
To mitigate this vulnerability, developers must ensure that CQ credit borrowing is strictly synchronized with connection lifecycle management. The fix involves setting a per-connection flag under con_mutex protection before initiating any teardown operations for Completion Queues and Queue Pairs. This flag acts as a guard rail, preventing the ADDR_RESOLVED handler from attempting to borrow credits once the teardown process has commenced. By enforcing this ordering, the race condition is eliminated because the address resolution logic will detect that the connection is being destroyed and abort the credit borrowing attempt. System administrators should apply kernel updates containing this patch immediately to restore proper resource accounting in RDMA subsystems. Additionally, monitoring for WARN_ON messages related to ib_cq_pool_cleanup in system logs can help identify systems still running vulnerable kernels where such race conditions may have occurred but not yet caused catastrophic failure.