linux-kernel - [PATCH V2] mptcp: pm: Fix uaf in __timer_delete

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Message-ID: <tencent_472581BA11BB2533E79EA21B964B2A1BC408@qq.com>
Date: Wed,  4 Sep 2024 09:01:37 +0800
From: Edward Adam Davis <eadavis@...com>
To: eadavis@...com
Cc: davem@...emloft.net,
	edumazet@...gle.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: [PATCH V2] 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).

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 | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
index 3e4ad801786f..d4cbf7dcf983 100644
--- a/net/mptcp/pm_netlink.c
+++ b/net/mptcp/pm_netlink.c
@@ -1430,8 +1430,10 @@ static bool remove_anno_list_by_saddr(struct mptcp_sock *msk,
 
 	entry = mptcp_pm_del_add_timer(msk, addr, false);
 	if (entry) {
+		spin_lock_bh(&msk->pm.lock);
 		list_del(&entry->list);
 		kfree(entry);
+		spin_unlock_bh(&msk->pm.lock);
 		return true;
 	}
 
-- 
2.43.0