From f88bb3606e4bd11ee035b682cddc2999e604609a Mon Sep 17 00:00:00 2001 From: Kyle Zeng Date: Wed, 7 Oct 2026 18:14:00 -0700 Subject: [PATCH] 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. Fixes: c428ecd1a21f ("netlink: Move namespace into hash key") Assisted-by: LLM Signed-off-by: Kyle Zeng Reviewed-by: Simon Horman Reviewed-by: Eric Dumazet Link: https://patch.msgid.link/20261008011359.63727-2-kylebot@openai.com Signed-off-by: Paolo Abeni --- net/netlink/af_netlink.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c index 01af3bb144ae..3029894edad1 100644 --- a/net/netlink/af_netlink.c +++ b/net/netlink/af_netlink.c @@ -464,7 +464,7 @@ netlink_unlock_table(void) struct netlink_compare_arg { - possible_net_t pnet; + u64 net_cookie; u32 portid; }; @@ -479,14 +479,14 @@ static inline int netlink_compare(struct rhashtable_compare_arg *arg, const struct netlink_sock *nlk = ptr; return nlk->portid != x->portid || - !net_eq(sock_net(&nlk->sk), read_pnet(&x->pnet)); + sock_net(&nlk->sk)->net_cookie != x->net_cookie; } static void netlink_compare_arg_init(struct netlink_compare_arg *arg, struct net *net, u32 portid) { memset(arg, 0, sizeof(*arg)); - write_pnet(&arg->pnet, net); + arg->net_cookie = net->net_cookie; arg->portid = portid; }