From: Eric Dumazet syzbot and Eulgyu Kim reported crashes in mptcp_pm_nl_get_local_id() and/or mptcp_pm_nl_is_backup() Root cause is list_splice_init() in mptcp_pm_nl_flush_addrs_doit() which is not RCU ready. list_splice_init_rcu() can not be called here while holding pernet->lock spinlock. Many thanks to Eulgyu Kim for providing a repro and testing our patches. Fixes: 141694df6573 ("mptcp: remove address when netlink flushes addrs") Signed-off-by: Eric Dumazet Reported-by: syzbot+5498a510ff9de39d37da@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/6970a46d.a00a0220.3ad28e.5cf0.GAE@google.com/T/ Reported-by: Eulgyu Kim Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/611 Reviewed-by: Mat Martineau Signed-off-by: Matthieu Baerts (NGI0) --- v3: - Same code, but the v2 was corrupted: leading whitespaces before tabs had been accidentally removed, causing 'git am' to reject the patch. - Add another Closes tag to MPTCP bug tracker. - Remove empty lines after 'spin_lock_bh()' to keep the same style. v2: - Make sure the list was not empty, return early otherwise. - https://lore.kernel.org/20260123030327.3041148-1-edumazet@google.com v1: - https://lore.kernel.org/20260122131306.2119853-1-edumazet@google.com --- net/mptcp/pm_kernel.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-) diff --git a/net/mptcp/pm_kernel.c b/net/mptcp/pm_kernel.c index 57570a44e418..b26675054b0d 100644 --- a/net/mptcp/pm_kernel.c +++ b/net/mptcp/pm_kernel.c @@ -1294,16 +1294,26 @@ static void __reset_counters(struct pm_nl_pernet *pernet) int mptcp_pm_nl_flush_addrs_doit(struct sk_buff *skb, struct genl_info *info) { struct pm_nl_pernet *pernet = genl_info_pm_nl(info); - LIST_HEAD(free_list); + struct list_head free_list; spin_lock_bh(&pernet->lock); - list_splice_init(&pernet->endp_list, &free_list); + free_list = pernet->endp_list; + INIT_LIST_HEAD_RCU(&pernet->endp_list); __reset_counters(pernet); pernet->next_id = 1; bitmap_zero(pernet->id_bitmap, MPTCP_PM_MAX_ADDR_ID + 1); spin_unlock_bh(&pernet->lock); - mptcp_nl_flush_addrs_list(sock_net(skb->sk), &free_list); + + if (free_list.next == &pernet->endp_list) + return 0; + synchronize_rcu(); + + /* Adjust the pointers to free_list instead of pernet->endp_list */ + free_list.prev->next = &free_list; + free_list.next->prev = &free_list; + + mptcp_nl_flush_addrs_list(sock_net(skb->sk), &free_list); __flush_addrs(&free_list); return 0; } --- base-commit: 8016dc5ee19a77678c264f8ba368b1e873fa705b change-id: 20260124-net-mptcp-race_nl_flush_addrs-337f460d1c9a Best regards, -- Matthieu Baerts (NGI0)