CVE-2024-38544 in Linux
Summary
by MITRE • 06/19/2024
In the Linux kernel, the following vulnerability has been resolved:
RDMA/rxe: Fix seg fault in rxe_comp_queue_pkt
In rxe_comp_queue_pkt() an incoming response packet skb is enqueued to the resp_pkts queue and then a decision is made whether to run the completer task inline or schedule it. Finally the skb is dereferenced to bump a 'hw' performance counter. This is wrong because if the completer task is already running in a separate thread it may have already processed the skb and freed it which can cause a seg fault. This has been observed infrequently in testing at high scale.
This patch fixes this by changing the order of enqueuing the packet until after the counter is accessed.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 10/21/2025
The vulnerability identified as CVE-2024-38544 represents a critical race condition within the Linux kernel's RDMA/rxe subsystem that can lead to system crashes through segmentation faults. This issue specifically affects the rxe_comp_queue_pkt function which handles incoming response packets in the RDMA over Ethernet implementation. The flaw occurs when processing packets through the resp_pkts queue where the kernel attempts to access hardware performance counters before properly managing the packet lifecycle, creating a scenario where concurrent execution paths can conflict with each other.
The technical implementation flaw stems from improper ordering of operations within the packet processing pipeline. When an incoming response packet arrives as an skb (socket buffer) structure, the kernel first enqueues this packet to the resp_pkts queue and then makes a decision about whether to execute the completer task synchronously or schedule it for later execution. The problematic sequence occurs when the code attempts to dereference the skb structure to increment a hardware performance counter after the queueing operation but before the completion decision is made. This ordering issue creates a window where a separate thread executing the completer task can process and free the same skb structure while the main thread is still attempting to access it, leading to a segmentation fault upon memory dereference.
This vulnerability operates at the kernel level within the RDMA subsystem, specifically targeting the rxe (RDMA over Ethernet) driver implementation that provides RDMA capabilities over standard ethernet networks. The flaw demonstrates characteristics consistent with CWE-367, which describes Time-of-Check to Time-of-Use (TOCTOU) vulnerabilities where the state of a resource changes between when it's checked and when it's used. The issue manifests as a segmentation fault that can cause system instability, potentially leading to complete system crashes or denial of service conditions in environments heavily utilizing RDMA networking capabilities. The infrequent occurrence in testing suggests this is a subtle race condition that only becomes apparent under high-scale network processing loads where concurrent execution paths are more likely to collide.
The operational impact of this vulnerability extends beyond simple system crashes to potentially compromise network reliability in high-performance computing environments where RDMA is extensively utilized. Systems running in data centers, high-performance computing clusters, or any environment requiring low-latency network communication through RDMA may experience unexpected service interruptions or complete system failures when this race condition is triggered. The vulnerability affects the kernel's ability to maintain stable packet processing for RDMA operations, which can cascade into broader network performance degradation or complete network stack failures. Organizations utilizing Linux systems with RDMA capabilities should consider this vulnerability particularly critical given the potential for unavailability in mission-critical network infrastructure.
Mitigation strategies for CVE-2024-38544 focus on applying the upstream kernel patch that reorders the packet processing operations to ensure proper resource management before hardware counter access. The fix implemented addresses the root cause by changing the sequence of operations so that the hardware performance counter is accessed before enqueuing the packet to the resp_pkts queue, preventing the race condition between the main execution path and the completer task thread. System administrators should prioritize updating to kernel versions containing this patch, particularly in production environments where RDMA networking is actively utilized. Additionally, monitoring for system instability or unexpected crashes in RDMA-enabled systems can help identify potential exploitation of this vulnerability before it causes complete service disruption. The patch addresses this through defensive programming practices that ensure proper resource lifecycle management in concurrent execution environments, aligning with best practices for kernel-level race condition prevention and memory safety.