CVE-2026-63990

Summary

In the Linux kernel, the following vulnerability has been resolved:

bonding: refuse to enslave CAN devices

syzbot reported a kernel paging request crash in can_rx_unregister() inside net/can/af_can.c. The crash occurs because a virtual CAN device (vxcan) is being enslaved to a bonding master.

During the enslavement process, the bonding driver mutates and modifies the network device states to fit an Ethernet-like aggregation model. However, CAN devices operate on a completely different Layer 2 architecture, relying on the CAN mid-layer private data structure (can_ml_priv) instead of standard Ethernet structures. Since bonding does not initialize or maintain these CAN structures, subsequent operations on the half-enslaved interface (such as closing associated sockets via isotp_release) lead to a null-pointer dereference when accessing the CAN receiver lists.

Bonding CAN interfaces is architecturally invalid as CAN lacks MAC addresses, ARP capabilities, and standard Ethernet link-layer mechanisms. While generic loopback devices are blocked globally in net/core/dev.c, virtual CAN devices bypass this check because they do not carry the IFF_LOOPBACK flag, despite acting as local software-loopbacks.

Fix this by explicitly blocking network devices of type ARPHRD_CAN from being enslaved at the very beginning of bond_enslave(). This prevents illegal state mutations, eliminates the resulting KASAN crashes, and avoids potential memory leaks from incomplete socket cleanups.

As the CAN support has been added a long time after bonding the Fixes-tag points to the introduction of ARPHRD_CAN that would have needed a specific handling in bonding_main.c.

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/69b78b5f3033272e53a2dc2dad675962654a5b38
• https://git.kernel.org/stable/c/41e8478c4cd896d3abbe33d41afc90c84ac66602
• https://git.kernel.org/stable/c/f4d78a81f57df82e9d82a2c07471fed1a1235893
• https://git.kernel.org/stable/c/02f1c87ded33b43d48b4a1d665da15f2157b30d8
• https://git.kernel.org/stable/c/9ea8a648d9120f7652bcde1ce2c4ad66871af707
• https://git.kernel.org/stable/c/563090e5d450c665f70d955a39f9587afc7842eb
• https://git.kernel.org/stable/c/8ba68464e4787b6a7ec938826e16124df20fd23d

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