linux-kernel - [PATCH net v3] mptcp: pm: Fix uaf in __timer_delete

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Message-ID: <tencent_F85DEC5DED99554FB28DEF258F8DB8120D07@qq.com>
Date: Thu,  5 Sep 2024 20:27:23 +0800
From: Edward Adam Davis <eadavis@...com>
To: matttbe@...nel.org
Cc: davem@...emloft.net,
	eadavis@...com,
	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: [PATCH net v3] 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".

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>
---
 net/mptcp/pm_netlink.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
index 3e4ad801786f..7ddb373cc6ad 100644
--- a/net/mptcp/pm_netlink.c
+++ b/net/mptcp/pm_netlink.c
@@ -329,17 +329,21 @@ struct mptcp_pm_add_entry *
 mptcp_pm_del_add_timer(struct mptcp_sock *msk,
 		       const struct mptcp_addr_info *addr, bool check_id)
 {
-	struct mptcp_pm_add_entry *entry;
 	struct sock *sk = (struct sock *)msk;
+	struct timer_list *add_timer = NULL;
+	struct mptcp_pm_add_entry *entry;
 
 	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;
+	}
 	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;
 }
@@ -1430,8 +1434,10 @@ 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