CVE-2026-43374net: nexthop: fix percpu use-after-free in remove_nh_grp_entry

Official description

In the Linux kernel, the following vulnerability has been resolved: net: nexthop: fix percpu use-after-free in remove_nh_grp_entry When removing a nexthop from a group, remove_nh_grp_entry() publishes the new group via rcu_assign_pointer() then immediately frees the removed entry's percpu stats with free_percpu(). However, the synchronize_net() grace period in the caller remove_nexthop_from_groups() runs after the free. RCU readers that entered before the publish still see the old group and can dereference the freed stats via nh_grp_entry_stats_inc() -> get_cpu_ptr(nhge->stats), causing a use-after-free on percpu memory. Fix by deferring the free_percpu() until after synchronize_net() in the caller. Removed entries are chained via nh_list onto a local deferred free list. After the grace period completes and all RCU readers have finished, the percpu stats are safely freed.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/abf4feaee6405f1441929c6ebe7a250f2cd170a7
• https://git.kernel.org/stable/c/ab5ebab9664214ba41a7633cb4e72f128204f924
• https://git.kernel.org/stable/c/9e08ad731862b22a87cc55f752e16d66cdc9e231
• https://git.kernel.org/stable/c/b2662e7593e94ae09b1cf7ee5f09160a3612bcb2