netdev - [PATCH v2 net] mptcp: fix race in mptcp_pm_nl_flush_addrs

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [day] [month] [year] [list]

Message-ID: <20260123030327.3041148-1-edumazet@google.com>
Date: Fri, 23 Jan 2026 03:03:27 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: Simon Horman <horms@...nel.org>, Matthieu Baerts <matttbe@...nel.org>, 
	Mat Martineau <martineau@...nel.org>, Geliang Tang <geliang.tang@...ux.dev>, 
	Florian Westphal <fw@...len.de>, netdev@...r.kernel.org, mptcp@...ts.linux.dev, 
	eric.dumazet@...il.com, Eric Dumazet <edumazet@...gle.com>, 
	syzbot+5498a510ff9de39d37da@...kaller.appspotmail.com, 
	Eulgyu Kim <eulgyukim@....ac.kr>, Geliang Tang <geliang@...nel.org>
Subject: [PATCH v2 net] mptcp: fix race in mptcp_pm_nl_flush_addrs_doit()

syzbot and Eulgyu Kim reported crashes in mptcp_pm_nl_get_local_id()
and/or mptcp_pm_nl_is_backup()

Root cause is list_splice_init() in mptcp_pm_nl_flush_addrs_doit()
which is not RCU ready.

list_splice_init_rcu() can not be called here while holding pernet->lock
spinlock.

Many thanks to Eulgyu Kim for providing a repro and testing our patches.

Fixes: 141694df6573 ("mptcp: remove address when netlink flushes addrs")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Reported-by: syzbot+5498a510ff9de39d37da@...kaller.appspotmail.com
Closes: https://lore.kernel.org/all/6970a46d.a00a0220.3ad28e.5cf0.GAE@google.com/T/
Reported-by: Eulgyu Kim <eulgyukim@....ac.kr>
Cc: Geliang Tang <geliang@...nel.org>
---
v2: Make sure the list was not empty, return early otherwise.
v1: https://lore.kernel.org/netdev/20260122131306.2119853-1-edumazet@google.com/

 net/mptcp/pm_kernel.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/net/mptcp/pm_kernel.c b/net/mptcp/pm_kernel.c
index 57570a44e4185370f531047fe97ce9f9fbd1480b..af23be6658ded4860133bb9495c7738014815d28 100644
--- a/net/mptcp/pm_kernel.c
+++ b/net/mptcp/pm_kernel.c
@@ -1294,16 +1294,28 @@ static void __reset_counters(struct pm_nl_pernet *pernet)
 int mptcp_pm_nl_flush_addrs_doit(struct sk_buff *skb, struct genl_info *info)
 {
	struct pm_nl_pernet *pernet = genl_info_pm_nl(info);
-	LIST_HEAD(free_list);
+	struct list_head free_list;

	spin_lock_bh(&pernet->lock);
-	list_splice_init(&pernet->endp_list, &free_list);
+
+	free_list = pernet->endp_list;
+	INIT_LIST_HEAD_RCU(&pernet->endp_list);
+
	__reset_counters(pernet);
	pernet->next_id = 1;
	bitmap_zero(pernet->id_bitmap, MPTCP_PM_MAX_ADDR_ID + 1);
	spin_unlock_bh(&pernet->lock);
-	mptcp_nl_flush_addrs_list(sock_net(skb->sk), &free_list);
+
+	if (free_list.next == &pernet->endp_list)
+		return 0;
+
	synchronize_rcu();
+
+	/* Adjust the pointers to free_list instead of pernet->endp_list */
+	free_list.prev->next = &free_list;
+	free_list.next->prev = &free_list;
+
+	mptcp_nl_flush_addrs_list(sock_net(skb->sk), &free_list);
	__flush_addrs(&free_list);
	return 0;
 }
--
2.52.0.457.g6b5491de43-goog