CVE-2026-99201netlink: avoid hashing the network namespace pointer

Official description

In the Linux kernel, the following vulnerability has been resolved: netlink: avoid hashing the network namespace pointer The netlink rhashtable key includes a raw struct net pointer and a user-controlled port ID. Both /proc/net/netlink and socket diagnostics expose the table's bucket order. By binding and rebinding chosen NETLINK_USERSOCK port IDs, an unprivileged reader can distinguish equal buckets and recover the low bits of the Jenkins hash. Its 32-bit seed and the limited set of kernel-image slides can then be searched offline to recover the address of init_net. Use the namespace's unique, non-address net_cookie in the comparison key instead. It is assigned before the per-net initializers run and remains unchanged for the namespace's lifetime. The lookup key and object hash are still built by netlink_compare_arg_init(), keeping lookup, insertion, removal and rehashing consistent while preserving namespace separation. Neither public table walker needs to change. Reading the socket's namespace cookie in netlink_compare() is safe under RCU, including during namespace teardown. netlink_release() removes the socket from the hash table and defers its final put with call_rcu(). cleanup_net() runs the per-net exit methods and waits for outstanding RCU callbacks with rcu_barrier() before freeing namespace storage. Unlike ns.ns_id, net_cookie is also available and initialized during setup_net() in older stable kernels, making the change straightforward to backport to v5.15 and later.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/c61431f3b8c9824e9848a0308054f92b27fa7794
• https://git.kernel.org/stable/c/f8d2690f3c5dfad1fc306f6d5d84a1d3176c3af9
• https://git.kernel.org/stable/c/c03fb9c4be3b2dd0996d91e54f65407f7f475238
• https://git.kernel.org/stable/c/41a2f69f091b0765f17890d8ac04852c12f25cf6
• https://git.kernel.org/stable/c/18edcb9945118beb7a1b64a31a7370ecab485a79
• https://git.kernel.org/stable/c/bdd55b8a8acbf6b4840ab420eb6a63774bf4593b
• https://git.kernel.org/stable/c/078deff25f8a849ecd1c3fe17b1e473b1cf44f28
• https://git.kernel.org/stable/c/f88bb3606e4bd11ee035b682cddc2999e604609a