linux-kernel - Re: [PATCH] mptcp: pm: Fix uaf in __timer_delete

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Message-ID: <tencent_EECBD37DC379497A63A1C455B773377AC605@qq.com>
Date: Wed,  4 Sep 2024 08:52:19 +0800
From: Edward Adam Davis <eadavis@...com>
To: edumazet@...gle.com
Cc: davem@...emloft.net,
	eadavis@...com,
	geliang@...nel.org,
	kuba@...nel.org,
	linux-kernel@...r.kernel.org,
	martineau@...nel.org,
	matttbe@...nel.org,
	mptcp@...ts.linux.dev,
	netdev@...r.kernel.org,
	pabeni@...hat.com,
	syzbot+f3a31fb909db9b2a5c4d@...kaller.appspotmail.com,
	syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH] mptcp: pm: Fix uaf in __timer_delete_sync

On Tue, 3 Sep 2024 17:18:42 +0200, Eric Dumazet <edumazet@...gle.com> wrote:
>On Tue, Sep 3, 2024 at 5:10 PM Edward Adam Davis <eadavis@...com> wrote:
>>
>> There are two paths to access mptcp_pm_del_add_timer, result in a race
>> condition:
>>
>>      CPU1                               CPU2
>>      ====                               ====
>>      net_rx_action
>>      napi_poll                          netlink_sendmsg
>>      __napi_poll                        netlink_unicast
>>      process_backlog                    netlink_unicast_kernel
>>      __netif_receive_skb                genl_rcv
>>      __netif_receive_skb_one_core       netlink_rcv_skb
>>      NF_HOOK                            genl_rcv_msg
>>      ip_local_deliver_finish            genl_family_rcv_msg
>>      ip_protocol_deliver_rcu            genl_family_rcv_msg_doit
>>      tcp_v4_rcv                         mptcp_pm_nl_flush_addrs_doit
>>      tcp_v4_do_rcv                      mptcp_nl_remove_addrs_list
>>      tcp_rcv_established                mptcp_pm_remove_addrs_and_subflows
>>      tcp_data_queue                     remove_anno_list_by_saddr
>>      mptcp_incoming_options             mptcp_pm_del_add_timer
>>      mptcp_pm_del_add_timer             kfree(entry)
>>
>> In remove_anno_list_by_saddr(running on CPU2), after leaving the critical
>> zone protected by "pm.lock", the entry will be released, which leads to the
>> occurrence of uaf in the mptcp_pm_del_add_timer(running on CPU1).
>>
>> Reported-and-tested-by: syzbot+f3a31fb909db9b2a5c4d@...kaller.appspotmail.com
>> Closes: https://syzkaller.appspot.com/bug?extid=f3a31fb909db9b2a5c4d
>> Signed-off-by: Edward Adam Davis <eadavis@...com>
>> ---
>>  net/mptcp/pm_netlink.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
>> index 3e4ad801786f..d28bf0c9ad66 100644
>> --- a/net/mptcp/pm_netlink.c
>> +++ b/net/mptcp/pm_netlink.c
>> @@ -336,11 +336,12 @@ mptcp_pm_del_add_timer(struct mptcp_sock *msk,
>>         entry = mptcp_lookup_anno_list_by_saddr(msk, addr);
>>         if (entry && (!check_id || entry->addr.id == addr->id))
>>                 entry->retrans_times = ADD_ADDR_RETRANS_MAX;
>> -       spin_unlock_bh(&msk->pm.lock);
>>
>>         if (entry && (!check_id || entry->addr.id == addr->id))
>>                 sk_stop_timer_sync(sk, &entry->add_timer);
>>
>> +       spin_unlock_bh(&msk->pm.lock);
>
>
>mptcp_pm_add_timer() needs to lock msk->pm.lock
>
>Your patch might add a deadlock, because sk_stop_timer_sync() is
Got it. MPTCP CI reported it.
>calling del_timer_sync()
>
>What is preventing this ?
I will change the strategy for protecting entry and use pm.lock to
synchronize when it is released in remove_anno_list_by_saddr.

Link: https://syzkaller.appspot.com/text?tag=Patch&x=124282ab980000

BR,
Edward