CVE-2026-98906 in Linux
Summary
by MITRE • 10/23/2026
In the Linux kernel, the following vulnerability has been resolved:
net: lan966x: restore RX state on reload failure
lan966x_fdma_reload() backs up rx->page_pool and rx->fdma before reallocating the RX resources for the new MTU. If the allocation fails, the restore path puts these fields back before restarting RX.
However, the reload path also updates rx->page_order and rx->max_mtu before calling lan966x_fdma_rx_alloc(). These fields are not restored on failure, so RX can be restarted with the old pages, old FDMA state and old page pool, but with the page geometry from the failed new MTU.
This can make the XDP path advertise a frame size derived from the new page_order while the actual RX pages still come from the old allocation. For example, after a failed reload to a jumbo MTU, xdp_init_buff() may be called with a frame size larger than the restored RX pages.
lan966x_fdma_rx_alloc_page_pool() also registers the newly allocated page pool with each port's XDP RXQ before fdma_alloc_coherent() is called. If fdma_alloc_coherent() fails, the new page pool is destroyed, but the rollback path does not restore the per-port XDP RXQ mem model registration either.
Save and restore rx->page_order and rx->max_mtu, and restore the old page pool registration for each port's XDP RXQ before RX is started again. This keeps the restored RX state consistent after a failed reload.
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Analysis
by VulDB Data Team • 10/23/2026
The vulnerability in the Linux kernel network driver lan966x stems from an incomplete rollback mechanism during resource reallocation, specifically within the fdma_reload function which handles changes to Maximum Transmission Unit settings. When the system attempts to resize receive buffers for a new MTU, it performs several state updates before attempting to allocate fresh memory resources. The process involves backing up critical structures such as rx->page_pool and rx->fdma to allow restoration in case of failure. However, the implementation fails to save and restore two crucial fields: rx->page_order and rx->max_mtu. These variables define the geometry of the allocated pages and the maximum supported frame size respectively. Consequently, if memory allocation for the new configuration fails, the driver restores the old page pool and FDMA state but leaves these geometric parameters updated to reflect the failed new MTU. This creates a critical inconsistency where the hardware or software path expects resources based on the larger jumbo frame geometry while actually operating with buffers sized for standard frames.
This discrepancy leads to severe operational instability, particularly affecting the eXpress Data Path XDP subsystem which relies heavily on accurate buffer size information. The xdp_init_buff function may be invoked with a frame size derived from the incorrect page_order value resulting in attempts to process packets that exceed the actual capacity of the restored RX pages. This mismatch can trigger kernel panics, memory corruption, or undefined behavior as the driver accesses memory beyond allocated boundaries. Such errors compromise system stability and reliability, potentially causing network interface crashes or data loss during high-throughput scenarios where MTU changes are attempted under resource pressure. The issue highlights a common class of bugs in low-level drivers where partial state restoration leaves internal consistency checks bypassed leading to unpredictable runtime failures rather than clean error returns that would allow higher layers to handle the failure gracefully.
From a security and standards perspective, this flaw aligns with CWE-672 which describes the use of operation-specific pointers without proper validation or synchronization ensuring data integrity before execution. It also relates to CWE-369 concerning race conditions in shared resources although here the issue is more about state inconsistency than concurrent access timing. In terms of MITRE ATT&CK, while not directly exploitable for remote code execution by an external attacker due to its dependency on local configuration changes and resource exhaustion this vulnerability represents a weakness that could be leveraged in denial-of-service attacks if triggered repeatedly or combined with other conditions leading to system instability. The lack of proper state rollback undermines the reliability guarantees expected from network drivers especially those handling high-performance packet processing paths like XDP which are often used for security functions such as firewalls and intrusion detection systems where consistent behavior is paramount.
To mitigate this vulnerability, developers must ensure that all state variables modified during a failed reallocation attempt are rolled back to their previous values before restarting the receive path. Specifically rx->page_order and rx->max_mtu need to be saved prior to modification and restored upon allocation failure alongside the existing page pool and FDMA structures. Additionally any registrations performed with per-port XDP RXQ memory models must also be undone if subsequent allocations fail preventing further inconsistencies in how buffers are interpreted by different subsystems. Implementing robust error handling that guarantees atomicity of state changes is essential for maintaining system integrity. System administrators should monitor driver logs for allocation failures and consider applying kernel updates or patches once available to resolve these internal logic errors ensuring consistent behavior across varying network configurations and load conditions preventing potential crashes during dynamic MTU adjustments.