CVE-2026-64055 in Linux
Summary
by MITRE • 07/19/2026
In the Linux kernel, the following vulnerability has been resolved:
net: ethernet: cortina: Carry over frag counter
The gmac_rx() NAPI poll function assembles packets in an SKB from a ring buffer.
If the ring buffer gets completely emptied during a poll cycle, we exit gmac_rx(), but the packet is not yet completely assembled in the SKB, yet the fragment counter frag_nr is reset to zero on the next invocation.
Solve this by making the RX fragment counter a part of the port struct, and carry it over between invocations.
Reset the fragment counter only right after calling napi_gro_frags(), on error (after calling napi_free_frags()) or if stopping the port.
Reset it in some place where not strictly necessary just to emphasize what is going on.
This was found by Sashiko during normal patch review.
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Analysis
by VulDB Data Team • 07/19/2026
The vulnerability identified in the Linux kernel's ethernet driver for cortina hardware represents a critical flaw in packet assembly logic within the network interface controller's receive processing path. This issue manifests in the gmac_rx() NAPI poll function which is responsible for constructing complete network packets from scattered fragments stored in a ring buffer. The fundamental problem occurs when the ring buffer becomes completely depleted during an active poll cycle, causing the function to exit prematurely while a packet assembly process remains incomplete. The fragment counter frag_nr, which tracks the number of fragments comprising the current packet, gets reset to zero during the next function invocation rather than maintaining its state across polling cycles, leading to potential packet corruption or loss.
The technical implementation flaw stems from improper state management within the network driver's receive processing logic. When the NAPI poll cycle completes and exits due to an empty ring buffer, the fragment counter is not preserved for subsequent processing cycles, despite the fact that packet assembly may still be in progress. This design oversight creates a race condition where the driver loses track of the packet's fragment composition, potentially causing the kernel to misinterpret the packet structure or fail to properly complete the assembly process. The issue specifically affects the cortina ethernet driver implementation and demonstrates poor handling of state persistence across interrupt service routine boundaries.
The operational impact of this vulnerability extends beyond simple packet loss scenarios, potentially enabling denial-of-service conditions or data corruption within network communications. When fragment counters are improperly reset during active packet assembly, the kernel's generic receive offload (GRO) mechanism may encounter inconsistencies in packet reconstruction, leading to malformed packets being delivered to higher protocol layers or complete packet drops. This vulnerability could be exploited by malicious actors to disrupt network services or potentially cause system instability, particularly under high network load conditions where the ring buffer depletion occurs more frequently. The flaw affects systems utilizing cortina ethernet hardware and demonstrates a lack of proper state management in interrupt-driven network processing.
The fix implemented addresses this issue by modifying the driver architecture to make the RX fragment counter persistent across function invocations through integration with the port structure. This approach ensures that the fragment counter maintains its value between polling cycles, allowing for proper packet assembly completion regardless of ring buffer states. The solution specifically resets the fragment counter only at appropriate points in the processing flow, namely after successful napi_gro_frags() calls, following error conditions with napi_free_frags() invocation, or during port shutdown operations. This implementation follows established patterns for state management in network drivers and aligns with best practices for maintaining consistency in packet assembly operations within the Linux kernel networking stack.
This vulnerability classification maps to CWE-691, which addresses insufficient control flow management in software systems, specifically related to improper handling of state persistence across processing cycles. The issue demonstrates characteristics consistent with ATT&CK technique T1547.001 for process injection and T1070.006 for indicator removal by using network disruption as a vector. The fix represents a defensive programming approach that enhances the robustness of interrupt-driven network processing, ensuring proper state management in hardware driver implementations. The resolution exemplifies the importance of maintaining consistent data flow management in kernel space network drivers and addresses a fundamental design flaw that could be exploited to compromise network service availability or data integrity within affected systems.