netdev - [PATCH net 1/2] mptcp: pm: Defer freeing of MPTCP userspace path manager entries

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Message-Id: <20250421-net-mptcp-pm-defer-freeing-v1-1-e731dc6e86b9@kernel.org>
Date: Mon, 21 Apr 2025 19:07:13 +0200
From: "Matthieu Baerts (NGI0)" <matttbe@...nel.org>
To: mptcp@...ts.linux.dev, Mat Martineau <martineau@...nel.org>, 
 Geliang Tang <geliang@...nel.org>, "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
 Shuah Khan <shuah@...nel.org>, Gang Yan <yangang@...inos.cn>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
 linux-kselftest@...r.kernel.org, 
 "Matthieu Baerts (NGI0)" <matttbe@...nel.org>, stable@...r.kernel.org
Subject: [PATCH net 1/2] mptcp: pm: Defer freeing of MPTCP userspace path
 manager entries

From: Mat Martineau <martineau@...nel.org>

When path manager entries are deleted from the local address list, they
are first unlinked from the address list using list_del_rcu(). The
entries must not be freed until after the RCU grace period, but the
existing code immediately frees the entry.

Use kfree_rcu_mightsleep() and adjust sk_omem_alloc in open code instead
of using the sock_kfree_s() helper. This code path is only called in a
netlink handler, so the "might sleep" function is preferable to adding
a rarely-used rcu_head member to struct mptcp_pm_addr_entry.

Fixes: 88d097316371 ("mptcp: drop free_list for deleting entries")
Cc: stable@...r.kernel.org
Signed-off-by: Mat Martineau <martineau@...nel.org>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@...nel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@...nel.org>
---
 net/mptcp/pm_userspace.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/net/mptcp/pm_userspace.c b/net/mptcp/pm_userspace.c
index 2cb62f026b1f4420c549ab8ee6f54ffe3880d453..a715dcbe0146ed0c055d071c63257047a90a9afd 100644
--- a/net/mptcp/pm_userspace.c
+++ b/net/mptcp/pm_userspace.c
@@ -337,7 +337,11 @@ int mptcp_pm_nl_remove_doit(struct sk_buff *skb, struct genl_info *info)

 	release_sock(sk);

-	sock_kfree_s(sk, match, sizeof(*match));
+	kfree_rcu_mightsleep(match);
+	/* Adjust sk_omem_alloc like sock_kfree_s() does, to match
+	 * with allocation of this memory by sock_kmemdup()
+	 */
+	atomic_sub(sizeof(*match), &sk->sk_omem_alloc);

 	err = 0;
 out:

-- 
2.48.1