Re: [PATCH v2 net] mptcp: fix race in mptcp_pm_nl_flush_addrs_doit()

[Matthieu Baerts <matttbe@kernel.org>]

Hi Mat, Eric,

On 23/01/2026 22:43, Mat Martineau wrote:
> On Fri, 23 Jan 2026, Eric Dumazet wrote:
> 
>> 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 <edumazet@google.com>
>> 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 <eulgyukim@snu.ac.kr>
>> Cc: Geliang Tang <geliang@kernel.org>
>> ---
>> v2: Make sure the list was not empty, return early otherwise.
> 
> Thanks Eric, the v2 code changes LGTM.

Thank you for the patch and the review!

> The netdev tooling wasn't able to
> apply the patch (https://patchwork.kernel.org/project/netdevbpf/
> patch/20260123030327.3041148-1-edumazet@google.com/), so Matthieu is
> planning to send a basically-identical v3 that 'git am' and the netdev
> CI will be happy with.

Just did:


https://lore.kernel.org/20260124-net-mptcp-race_nl_flush_addrs-v3-1-b2dc1b613e9d@kernel.org

I guess we need to manually update Patchwork if the sender is different:

pw-bot: superseded

Cheers,
Matt
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