Commit e2a9eeb6 authored by Eric Dumazet's avatar Eric Dumazet Committed by Jakub Kicinski
Browse files

mptcp: fix race in mptcp_pm_nl_flush_addrs_doit() 



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: 141694df ("mptcp: remove address when netlink flushes addrs")
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Reported-by: default avatar <syzbot+5498a510ff9de39d37da@syzkaller.appspotmail.com>
Closes: https://lore.kernel.org/all/6970a46d.a00a0220.3ad28e.5cf0.GAE@google.com/T/


Reported-by: default avatarEulgyu Kim <eulgyukim@snu.ac.kr>
Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/611


Reviewed-by: default avatarMat Martineau <martineau@kernel.org>
Signed-off-by: default avatarMatthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20260124-net-mptcp-race_nl_flush_addrs-v3-1-b2dc1b613e9d@kernel.org


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 8d7ba71e

net/mptcp/pm_kernel.c

+13 −3
Original line number Diff line number Diff line
@@ -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;

}