Re: [PATCH net v3] mptcp: pm: Fix uaf in __timer_delete_sync

[Matthieu Baerts]

Hi Edward,

On 05/09/2024 14:27, 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".
> 
> Fixes: 00cfd77b9063 ("mptcp: retransmit ADD_ADDR when timeout")
> Cc: stable@xxxxxxxxxxxxxxx
> Reported-and-tested-by: syzbot+f3a31fb909db9b2a5c4d@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=f3a31fb909db9b2a5c4d
> Signed-off-by: Matthieu Baerts (NGI0) <matttbe@xxxxxxxxxx>

According to the doc [1], a 'Co-dev' tag is supposed to be added before
this SoB:

Co-developed-by: Matthieu Baerts (NGI0) <matttbe@xxxxxxxxxx>

But I'm sure that's fine without it.

[1]
https://docs.kernel.org/process/submitting-patches.html#when-to-use-acked-by-cc-and-co-developed-by


This v3 now looks good to me. I don't know if it needs to be reviewed by
someone else as I'm now listed as co-developed.

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