Re: [PATCH net V4] mptcp: pm: Fix uaf in __timer_delete_sync

[Paolo Abeni]

On 9/10/24 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@xxxxxxxxxxxxxxx
> Reported-and-tested-by: syzbot+f3a31fb909db9b2a5c4d@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=f3a31fb909db9b2a5c4d
> Signed-off-by: Matthieu Baerts (NGI0) <matttbe@xxxxxxxxxx>
> Signed-off-by: Edward Adam Davis <eadavis@xxxxxx>

Acked-by: Paolo Abeni <pabeni@xxxxxxxxxx>