[ Conflicts because the code has been moved from pm_netlink.c to
pm_kernel.c later on in commit 8617e85e04bd ("mptcp: pm: split in-kernel PM specific code"). The same modifications can be applied in pm_netlink.c with one exception, because 'pernet->local_addr_list' has been renamed to 'pernet->endp_list' in commit 35e71e43a56d ("mptcp: pm: in-kernel: rename 'local_addr_list' to 'endp_list'"). The previous name is then still being used in this version. Also, another conflict is caused by commit 7bcf4d8022f9 ("mptcp: pm:
rename helpers linked to 'flush'") which is not in this version:
mptcp_nl_remove_addrs_list() has been renamed to mptcp_nl_flush_addrs_list(). The previous name has then been kept. ]

Signed-off-by Matthieu Baerts (NGI0) <[email protected]>

---
 net/mptcp/pm_netlink.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

net/mptcp/pm_netlink.c +13 -3

index cc58536bbf26..293ec3448f52 100644
@@ -1855,16 +1855,26 @@ static void __reset_counters(struct pm_nl_pernet *pernet)
 static int mptcp_nl_cmd_flush_addrs(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->local_addr_list, &free_list);
+	free_list = pernet->local_addr_list;
+	INIT_LIST_HEAD_RCU(&pernet->local_addr_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_remove_addrs_list(sock_net(skb->sk), &free_list);
+
+	if (free_list.next == &pernet->local_addr_list)
+		return 0;
+
 	synchronize_rcu();
+
+	/* Adjust the pointers to free_list instead of pernet->local_addr_list */
+	free_list.prev->next = &free_list;
+	free_list.next->prev = &free_list;
+
+	mptcp_nl_remove_addrs_list(sock_net(skb->sk), &free_list);
 	__flush_addrs(&free_list);
 	return 0;
 }

Signature · 1 line

2.51.0

[email protected]

maintainer Applied

2026-02-17 12:33 UTC #1 lore raw

Patch "mptcp: fix race in mptcp_pm_nl_flush_addrs_doit()" has been added to the 6.1-stable tree

This is a note to let you know that I've just added the patch titled

mptcp: fix race in mptcp_pm_nl_flush_addrs_doit()

to the 6.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mptcp-fix-race-in-mptcp_pm_nl_flush_addrs_doit.patch
and it can be found in the queue-6.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From [email protected] Thu Feb 12 18:41:08 2026
From: "Matthieu Baerts (NGI0)" <[email protected]>
Date: Thu, 12 Feb 2026 18:40:52 +0100
Subject: mptcp: fix race in mptcp_pm_nl_flush_addrs_doit()
To: [email protected], [email protected]
Cc: MPTCP Upstream <[email protected]>, Eric Dumazet <[email protected]>, [email protected], Eulgyu Kim <[email protected]>, Mat Martineau <[email protected]>, "Matthieu Baerts (NGI0)" <[email protected]>, Jakub Kicinski <[email protected]>
Message-ID: <[email protected]>

From: Eric Dumazet <[email protected]>

commit e2a9eeb69f7d4ca4cf4c70463af77664fdb6ab1d upstream.

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 <[email protected]>

Reported-by [email protected]

Closes https://lore.kernel.org/all/[email protected]/T/ open here

Reported-by Eulgyu Kim <[email protected]>

Closes https://github.com/multipath-tcp/mptcp_net-next/issues/611

Reviewed-by Mat Martineau <[email protected]>

Signed-off-by Matthieu Baerts (NGI0) <[email protected]>

Link https://patch.msgid.link/20260124-net-mptcp-race_nl_flush_addrs-v3-1-b2dc1b613e9d@kernel.org open here

Signed-off-by Jakub Kicinski <[email protected]>

Signed-off-by Matthieu Baerts (NGI0) <[email protected]>

Signed-off-by Greg Kroah-Hartman <[email protected]>

---
 net/mptcp/pm_netlink.c |   16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

net/mptcp/pm_netlink.c +13 -3

@@ -1855,16 +1855,26 @@ static void __reset_counters(struct pm_n
 static int mptcp_nl_cmd_flush_addrs(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->local_addr_list, &free_list);
+	free_list = pernet->local_addr_list;
+	INIT_LIST_HEAD_RCU(&pernet->local_addr_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_remove_addrs_list(sock_net(skb->sk), &free_list);
+
+	if (free_list.next == &pernet->local_addr_list)
+		return 0;
+
 	synchronize_rcu();
+
+	/* Adjust the pointers to free_list instead of pernet->local_addr_list */
+	free_list.prev->next = &free_list;
+	free_list.next->prev = &free_list;
+
+	mptcp_nl_remove_addrs_list(sock_net(skb->sk), &free_list);
 	__flush_addrs(&free_list);
 	return 0;
 }

Patches currently in stable-queue which might be from [email protected] are

queue-6.1/selftests-mptcp-join-fix-local-endp-not-being-tracked.patch queue-6.1/mptcp-fix-race-in-mptcp_pm_nl_flush_addrs_doit.patch queue-6.1/mptcp-schedule-rtx-timer-only-after-pushing-data.patch queue-6.1/mptcp-ensure-context-reset-on-disconnect.patch queue-6.1/selftests-mptcp-pm-ensure-unknown-flags-are-ignored.patch queue-6.1/selftests-mptcp-check-no-dup-close-events-after-error.patch queue-6.1/selftests-mptcp-check-subflow-errors-in-close-events.patch