CVE-2026-23300

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> net: ipv6: fix panic when IPv4 route references loopback IPv6 nexthop<br /> <br /> When a standalone IPv6 nexthop object is created with a loopback device<br /> (e.g., "ip -6 nexthop add id 100 dev lo"), fib6_nh_init() misclassifies<br /> it as a reject route. This is because nexthop objects have no destination<br /> prefix (fc_dst=::), causing fib6_is_reject() to match any loopback<br /> nexthop. The reject path skips fib_nh_common_init(), leaving<br /> nhc_pcpu_rth_output unallocated. If an IPv4 route later references this<br /> nexthop, __mkroute_output() dereferences NULL nhc_pcpu_rth_output and<br /> panics.<br /> <br /> Simplify the check in fib6_nh_init() to only match explicit reject<br /> routes (RTF_REJECT) instead of using fib6_is_reject(). The loopback<br /> promotion heuristic in fib6_is_reject() is handled separately by<br /> ip6_route_info_create_nh(). After this change, the three cases behave<br /> as follows:<br /> <br /> 1. Explicit reject route ("ip -6 route add unreachable 2001:db8::/64"):<br /> RTF_REJECT is set, enters reject path, skips fib_nh_common_init().<br /> No behavior change.<br /> <br /> 2. Implicit loopback reject route ("ip -6 route add 2001:db8::/32 dev lo"):<br /> RTF_REJECT is not set, takes normal path, fib_nh_common_init() is<br /> called. ip6_route_info_create_nh() still promotes it to reject<br /> afterward. nhc_pcpu_rth_output is allocated but unused, which is<br /> harmless.<br /> <br /> 3. Standalone nexthop object ("ip -6 nexthop add id 100 dev lo"):<br /> RTF_REJECT is not set, takes normal path, fib_nh_common_init() is<br /> called. nhc_pcpu_rth_output is properly allocated, fixing the crash<br /> when IPv4 routes reference this nexthop.