mptcp: pm: Fix uaf in __timer_delete_sync

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@vger.kernel.org
Reported-and-tested-by: syzbot+f3a31fb909db9b2a5c4d@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=f3a31fb909db9b2a5c4d
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
Acked-by: Paolo Abeni <pabeni@redhat.com>
Link: https://patch.msgid.link/tencent_7142963A37944B4A74EF76CD66EA3C253609@qq.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
index f891bc714668c56ad80b97fbe1487fcb48399878..ad935d34c973a97a637cfb359842dc6004e78ff0 100644 (file)
--- a/net/mptcp/pm_netlink.c
+++ b/net/mptcp/pm_netlink.c
@@ -334,15 +334,21 @@ mptcp_pm_del_add_timer(struct mptcp_sock *msk,
 {
        struct mptcp_pm_add_entry *entry;
        struct sock *sk = (struct sock *)msk;
+       struct timer_list *add_timer = NULL;
 
        spin_lock_bh(&msk->pm.lock);
        entry = mptcp_lookup_anno_list_by_saddr(msk, addr);
-       if (entry && (!check_id || entry->addr.id == addr->id))
+       if (entry && (!check_id || entry->addr.id == addr->id)) {
                entry->retrans_times = ADD_ADDR_RETRANS_MAX;
+               add_timer = &entry->add_timer;
+       }
+       if (!check_id && entry)
+               list_del(&entry->list);
        spin_unlock_bh(&msk->pm.lock);
 
-       if (entry && (!check_id || entry->addr.id == addr->id))
-               sk_stop_timer_sync(sk, &entry->add_timer);
+       /* no lock, because sk_stop_timer_sync() is calling del_timer_sync() */
+       if (add_timer)
+               sk_stop_timer_sync(sk, add_timer);
 
        return entry;
 }
@@ -1462,7 +1468,6 @@ static bool remove_anno_list_by_saddr(struct mptcp_sock *msk,
 
        entry = mptcp_pm_del_add_timer(msk, addr, false);
        if (entry) {
-               list_del(&entry->list);
                kfree(entry);
                return true;
        }