CVE-2026-93107 in Linux
Summary
by MITRE • 09/18/2026
In the Linux kernel, the following vulnerability has been resolved:
RDMA/rxe: Avoid reprocessing the current packet after the QP enters the error state
When do_complete() finds the QP in the error state it returns RESPST_CHK_RESOURCE. Before commit 49dc9c1f0c7e ("RDMA/rxe: Cleanup reset state handling in rxe_resp.c") this was the flush loop: check_resource() had an error-state branch that fetched each remaining recv WQE and completed it with IB_WC_WR_FLUSH_ERR, without touching the current packet. That commit removed the error-state branch from check_resource() (draining is now done at rxe_receiver() entry) but kept the do_complete() error-state return.
As a result, when a QP moves to the error state while a packet is being completed - e.g. an rdma_cm disconnect racing with receive processing - the responder state machine loops back into the request processing chain with the already-completed packet still in hand: check_resource() fetches a fresh recv WQE, execute()/send_data_in() copies the same packet payload again, do_complete() posts another IB_WC_SUCCESS CQE (qp->resp.status is still 0), and control returns to the error-state check. The loop re-executes the same packet once per posted recv WQE (observed: ~1000 duplicate IB_WC_SUCCESS completions of one SEND, one per ~8us, matching the RQ occupancy) until the RQ is exhausted, after which qp->resp.wqe is NULL and send_data_in() dereferences it:
BUG: kernel NULL pointer dereference, address: 0000000000000014 Workqueue: rxe_wq do_work RIP: copy_data+0x29/0x1f0 Call Trace: send_data_in+0x25/0x50 rxe_receiver+0xf36/0x1dd0
The duplicate completions are indistinguishable from real receives to the ULP. During an rds stress test, the message was accepted as new and delivered the same datagram to user space hundreds of times, corrupting the stream; any ULP that relies on RC exactly-once delivery is affected.
A live packet reaching the error-state check in do_complete() has been executed and completed exactly once and must be consumed, not re-processed. Return RESPST_CLEANUP for it (dequeue and free); keep returning RESPST_CHK_RESOURCE for the pkt == NULL case.
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Analysis
by VulDB Data Team • 09/18/2026
The Linux kernel's RDMA over Converged Ethernet implementation contains a logic flaw in the responder state machine that leads to packet duplication, resource exhaustion, and ultimately a null pointer dereference crash when a Queue Pair transitions to an error state during active processing. This vulnerability stems from an incomplete cleanup following commit 49dc9c1f0c7e which refactored reset state handling within rxe_resp.c. Previously, the check_resource function contained specific logic to handle error states by draining remaining receive Work Queue Elements and completing them with a flush error code without reprocessing the current packet. The recent refactor moved this draining logic to the entry of the receiver routine but failed to adjust the do_complete function's behavior when it detects an error state while processing a valid packet.
When a Queue Pair enters the error state, such as during a race condition between an rdma_cm disconnect and receive processing, the responder state machine incorrectly loops back into the request processing chain with the already-completed packet still in hand. The check_resource function fetches a fresh receive Work Queue Element and executes send_data_in which copies the same packet payload again. Consequently, do_complete posts another IB_WC_SUCCESS Completion Queue Entry despite qp->resp.status remaining zero because it was never updated to reflect the error state during this specific loop iteration. This creates an infinite or near-infinite loop where the same packet is re-executed once per posted receive Work Queue Element until the queue is exhausted.
The operational impact of this flaw is severe for both system stability and data integrity. The duplicate completions are indistinguishable from legitimate receives to the Upper Layer Protocol, leading to significant application-level corruption. In stress testing scenarios involving RDS, messages were accepted as new and delivered hundreds of times to user space, effectively corrupting the stream and violating exactly-once delivery guarantees required by reliable connection protocols. Furthermore, once the receive queue is exhausted due to this loop, qp->resp.wqe becomes NULL. The subsequent call to send_data_in attempts to dereference this null pointer, resulting in a kernel BUG with a null pointer dereference at address 0x14 within copy_data, causing a system crash or denial of service for the affected workload.
From a vulnerability classification perspective, this issue aligns with CWE-835 which describes loops that do not terminate properly due to logic errors leading to resource exhaustion and potential crashes. It also relates to CWE-20 regarding improper input validation where the state transition does not correctly invalidate or consume pending operations before proceeding. In terms of attack vectors, while primarily a stability issue triggered by race conditions rather than direct exploitation for code execution, it impacts availability which is critical under ATT&CK technique T1499 Endpoint Denial of Service. The vulnerability allows an attacker who can trigger rapid state changes on RDMA connections to destabilize the kernel or corrupt application data streams.
The resolution involves modifying do_complete to return RESPST_CLEANUP for live packets that reach the error-state check, ensuring they are dequeued and freed rather than re-processed. This change preserves the existing behavior of returning RESPST_CHK_RESOURCE only when the packet pointer is null, which correctly handles cases where no work is pending. Mitigation strategies include applying the kernel patch immediately to update the responder state machine logic. System administrators should also monitor for unusual spikes in completion queue entries and system logs indicating null pointer dereferences during high-load RDMA operations as indicators of this race condition occurring before a fix is deployed.