CVE-2026-90080 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
octeontx2-pf: fix NULL deref of af_xdp_zc_qidx on rep setup
af_xdp_zc_qidx tracks receive queues using AF_XDP zero-copy and is allocated during PF/VF probe. Representors and other non-AF_XDP paths leave the pointer NULL, but several call sites used test_bit() on it unconditionally.
Switching to devlink eswitch mode creates representors and runs otx2_init_hw_resources(), which reaches otx2_pool_aq_init() and oopses when dereferencing the NULL bitmap. Add NULL checks before every af_xdp_zc_qidx test_bit() use in the RSS, ethtool, XSK, and pool init paths.
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Analysis
by VulDB Data Team • 09/17/2026
The Linux kernel vulnerability identified as octeontx2-pf involves a null pointer dereference within the network driver subsystem, specifically affecting the AF_XDP zero-copy queue index management logic. This issue arises from an inconsistency in how receive queues are tracked for different interface types during hardware initialization and configuration phases. The variable af_xdp_zc_qidx is designed to track receive queues utilizing AF_XDP zero-copy functionality and is allocated only when a Physical Function or Virtual Function probe occurs successfully with this specific feature enabled. However, representors and other non-AF_XDP operational paths do not initialize this pointer, leaving it as NULL. Despite this conditional allocation, several critical code sites within the driver attempted to test bits on this bitmap unconditionally using the test_bit() macro without verifying that the underlying pointer was valid before access.
The operational impact of this flaw becomes apparent when switching the device to devlink eswitch mode, a configuration commonly used for advanced networking features such as SR-IOV and virtual switch offloading. This action triggers the creation of representor interfaces and initiates hardware resource initialization through otx2_init_hw_resources(). During this process, the function otx2_pool_aq_init() is invoked, which subsequently attempts to access af_xdp_zc_qidx via test_bit(). Because the pointer remains NULL for these non-AF_XDP paths, the kernel encounters a null pointer dereference exception. This results in an immediate system crash or panic, effectively causing a denial of service condition where the network interface becomes unavailable and potentially destabilizes the entire host operating system depending on kernel panic settings.
From a vulnerability classification perspective, this defect aligns with CWE-476, which denotes a NULL pointer dereference error. The root cause lies in insufficient input validation or state checking prior to memory access operations. In terms of attack vectors, while this is primarily an internal driver logic flaw rather than an externally exploitable remote code execution vector, it can be triggered by local users with appropriate privileges to modify network interface configurations via devlink commands. This maps closely to ATT&CK technique T1562, specifically Impair Defenses through Disable or Modify Cloud Infrastructure Tools, as misconfiguration of networking components leads to service disruption. The vulnerability highlights the risks associated with assuming uniform state across different hardware abstraction layers without explicit checks for feature support or initialization status.
Mitigation strategies require both immediate patching and long-term defensive coding practices. The primary resolution involves modifying the octeontx2-pf driver code to insert NULL checks before every invocation of test_bit() on af_xdp_zc_qidx across all relevant paths, including RSS configuration, ethtool operations, XSK setup, and pool initialization routines. Developers must ensure that any bitmap or pointer accessed in this manner is validated against nullity prior to dereferencing. For system administrators unable to apply kernel patches immediately, restricting the use of devlink eswitch mode on affected hardware until an update is available serves as a temporary workaround. Additionally, enforcing strict code review processes for driver development and utilizing static analysis tools that detect potential NULL pointer accesses can prevent similar defects in future releases.