From nobody Mon Mar 2 06:35:36 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id AD9711E9B3F; Thu, 12 Feb 2026 17:41:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770918062; cv=none; b=ESDXc8mnH0k6ZRoPxO1M30v7+6LLATBLm+T6pQa//kcWs5TtT1bQqL+5D9dsMngFimI6HkiqAfPDn64/3JsUdkZgBca/5O09Je1MPGdEPbC2caqpHyA5JOqyjeiCj2PNWrJBIZnLn1W8vEltCTW4wj814gn/mc9Z14Xh2j430EQ= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770918062; c=relaxed/simple; bh=JuoZWuJHqqx1DXrYnnJxtG+Mlw2QkrQua4Z4MNJSUGU=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=fK0XkOvpkJA/EoqZPNJYjZ90yLZ5LR13dj+kJmx0iIc9ltmDW6Nn4H6bHkP/uLbgTrje4sRqFehw38VLDQkAqY2mqzfpMWu7MeU8yEvWQpqM8uA9bPOLLs9MOZ0WyRfHnSIkvM1cTkBzwSGZXD3NAzhAEO7Oo5LUObGUiABR7sw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=pmKBOhdt; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="pmKBOhdt" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 968EDC4CEF7; Thu, 12 Feb 2026 17:41:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1770918062; bh=JuoZWuJHqqx1DXrYnnJxtG+Mlw2QkrQua4Z4MNJSUGU=; h=From:To:Cc:Subject:Date:From; b=pmKBOhdt691RM+hQQb++sI49fryqSv+dkGWH1D1ft7ah+cDgP3m0y4Mf2sJ5gvpha Qvp1H+5ukxFt8CsqONt2xefA5OEDW3tQlImNqhOc+IhjGdt+eZTFLQGl5itSsHOvZe 3vTwrIRHNjhQK0v9oAJBLWBdIw+vTYDxie5/JHWR5V8TyxMx6W/bfZpn39bB8cAlWn vpq4mkteOmbfxN4/VEsZFYl8xnCaU/+HU2cQsGxl5RzbsBOvjQU2OLme01boRvGm0T lURMp727GQwhwpwYH+VT663UE3yclloG25u9dr9rwoBUvELrbPlHKsLWneLoHn5QSN KTHlK7MD07KpQ== From: "Matthieu Baerts (NGI0)" To: stable@vger.kernel.org, gregkh@linuxfoundation.org Cc: MPTCP Upstream , Eric Dumazet , syzbot+5498a510ff9de39d37da@syzkaller.appspotmail.com, Eulgyu Kim , Mat Martineau , "Matthieu Baerts (NGI0)" , Jakub Kicinski Subject: [PATCH 6.1.y] mptcp: fix race in mptcp_pm_nl_flush_addrs_doit() Date: Thu, 12 Feb 2026 18:40:52 +0100 Message-ID: <20260212174051.1839592-2-matttbe@kernel.org> X-Mailer: git-send-email 2.51.0 Precedence: bulk X-Mailing-List: mptcp@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=3192; i=matttbe@kernel.org; h=from:subject; bh=W5rjCbGOcVM2iHsdt8PD8IQL8WF3OCFnV/IhyOBrL5Y=; b=owGbwMvMwCVWo/Th0Gd3rumMp9WSGDL7BJZsDPJZm3ddNE2n6sT2vD21E8+aRrLq32pYnLpfx 65j68XajlIWBjEuBlkxRRbptsj8mc+reEu8/Cxg5rAygQxh4OIUgIkwn2FkOHzMfoXy0bw5Xyed U/sb9trT4RzTwUfr72lbFd66uMRvrQnDf59Tgmza7REHWI5srXVJu161WeKNr9ckszfaE4Wz/Y+ /ZQEA X-Developer-Key: i=matttbe@kernel.org; a=openpgp; fpr=E8CB85F76877057A6E27F77AF6B7824F4269A073 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Eric Dumazet 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 Reported-by: syzbot+5498a510ff9de39d37da@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/6970a46d.a00a0220.3ad28e.5cf0.GAE@googl= e.com/T/ Reported-by: Eulgyu Kim Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/611 Reviewed-by: Mat Martineau Signed-off-by: Matthieu Baerts (NGI0) Link: https://patch.msgid.link/20260124-net-mptcp-race_nl_flush_addrs-v3-1-= b2dc1b613e9d@kernel.org Signed-off-by: Jakub Kicinski [ 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) --- net/mptcp/pm_netlink.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-) diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c index cc58536bbf26..293ec3448f52 100644 --- a/net/mptcp/pm_netlink.c +++ b/net/mptcp/pm_netlink.c @@ -1855,16 +1855,26 @@ static void __reset_counters(struct pm_nl_pernet *p= ernet) static int mptcp_nl_cmd_flush_addrs(struct sk_buff *skb, struct genl_info = *info) { struct pm_nl_pernet *pernet =3D genl_info_pm_nl(info); - LIST_HEAD(free_list); + struct list_head free_list; =20 spin_lock_bh(&pernet->lock); - list_splice_init(&pernet->local_addr_list, &free_list); + free_list =3D pernet->local_addr_list; + INIT_LIST_HEAD_RCU(&pernet->local_addr_list); __reset_counters(pernet); pernet->next_id =3D 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 =3D=3D &pernet->local_addr_list) + return 0; + synchronize_rcu(); + + /* Adjust the pointers to free_list instead of pernet->local_addr_list */ + free_list.prev->next =3D &free_list; + free_list.next->prev =3D &free_list; + + mptcp_nl_remove_addrs_list(sock_net(skb->sk), &free_list); __flush_addrs(&free_list); return 0; } --=20 2.51.0