netdev - Re: [PATCH net V4] mptcp: pm: Fix uaf in __timer_delete

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Message-ID: <8ad4406e-cdd3-4204-928e-6ac6dd628cbc@kernel.org>
Date: Tue, 10 Sep 2024 16:29:38 +0200
From: Matthieu Baerts <matttbe@...nel.org>
To: Edward Adam Davis <eadavis@...com>
Cc: davem@...emloft.net, edumazet@...gle.com, geliang@...nel.org,
 kuba@...nel.org, linux-kernel@...r.kernel.org, martineau@...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 net V4] mptcp: pm: Fix uaf in __timer_delete_sync

Hi Edward,

On 10/09/2024 11:58, Edward Adam Davis 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).
> 
> Keeping a reference to add_timer inside the lock, and calling
> sk_stop_timer_sync() with this reference, instead of "entry->add_timer".
> 
> Move list_del(&entry->list) to mptcp_pm_del_add_timer and inside the pm lock,
> do not directly access any members of the entry outside the pm lock, which
> can avoid similar "entry->x" uaf.
> 
> Fixes: 00cfd77b9063 ("mptcp: retransmit ADD_ADDR when timeout")
> Cc: stable@...r.kernel.org
> Reported-and-tested-by: syzbot+f3a31fb909db9b2a5c4d@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=f3a31fb909db9b2a5c4d
> Signed-off-by: Matthieu Baerts (NGI0) <matttbe@...nel.org>
> Signed-off-by: Edward Adam Davis <eadavis@...com>
It looks also good to me, but no need for me to add a reviewed-by tag I
suppose.

This v4 can be applied in netdev directly.

Cheers,
Matt
-- 
Sponsored by the NGI0 Core fund.