From nobody Fri Apr 3 07:55:20 2026 Received: from mail-yw1-f180.google.com (mail-yw1-f180.google.com [209.85.128.180]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8CFFA346A1B for ; Wed, 18 Feb 2026 18:11:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.180 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771438275; cv=none; b=WNKg6C53TOPAG0ZoUnTiaRweDX4QOanNnNPWpX1jNGu8ynwIRCiCyqmM1+Ar8vjGsqXs0GgSkAMdOmYMi9WIX8CQ7ja6VGxUtrQQIWfDL6lPSF79eAJ4z0huri83UtdPE5iOY9VMLFoiy6p23tts3VRpUj5S4kbItPvuqh3xys4= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771438275; c=relaxed/simple; bh=nlAlDEhBcV2bHlFAryaUj7ZOcWtIQPl+cHubqkhJz4A=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=FYGgA8gDfmQ4oEgSNpWJ1SgJB8S62bv3uFMU9i9Kn1tDq7h0U6bntxa338qPwTzX7jpGw2D+ta8+ywRjcoeAHjH7oZjA0rqT/T+f5NNBKT/OZprMgjQNVvgC43KtKSxtllLoySI9mgPfTdjnyR1VAK5q9BsHHyX50faJ+lNHtK0= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=hUp7oJdp; arc=none smtp.client-ip=209.85.128.180 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="hUp7oJdp" Received: by mail-yw1-f180.google.com with SMTP id 00721157ae682-79427f739b0so956847b3.3 for ; Wed, 18 Feb 2026 10:11:13 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1771438273; x=1772043073; darn=vger.kernel.org; h=cc:to:in-reply-to:references:message-id:content-transfer-encoding :mime-version:subject:date:from:from:to:cc:subject:date:message-id :reply-to; bh=EYXQVsGZ6QB5W8jT2tab5YPGUexmQcws943nTeNPNNs=; b=hUp7oJdp3Hotae+s6O2fU5aY27/6OUVkspJ/J1FKgfyZnP1J8y3i/tT0h+me+TXuVz LFZnwKmOMEZjCPwT9kZy0MxO3u2adyIArKxflc79iNOk1+meLeqJgvG+UddxMJGU7k95 X1yc/DoHlDbA5gSEUF65wXAMXpdXQG9hMpv8Urdy3h0zdinnnEJOH6amloSk26ufsenZ xwYZYGz9d2xwSXYpdtIhwVSha3eSG+QU3dh+zZ9L85SyHX0X6agnkTRV+v2wcV5TKnSH NP6bngIRgVCtAUmOvC9nKQRRMNpFKei1Ze1UpUimKVaE+994K9sCpjnMJLo9ZeOBSuv0 HmLg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1771438273; x=1772043073; h=cc:to:in-reply-to:references:message-id:content-transfer-encoding :mime-version:subject:date:from:x-gm-gg:x-gm-message-state:from:to :cc:subject:date:message-id:reply-to; bh=EYXQVsGZ6QB5W8jT2tab5YPGUexmQcws943nTeNPNNs=; b=UQSNgDz9Tl8/JQr5XOFAAzU8bcO2vbTODCBcI75KUPqh2j4dA4z2eGH6wf1ZArhWRW 8MO9wstnGaqLgLWgYlum95gesIiVIsaA+WkBUTUoB0pmxClIsOqNZTkh4bb3fd8WNuet BAIeqa/DJ7BVXMH6CIvaRhn/RSHWGpbRHfxJl6HCxO+HzRTjdKwg1Xjk9ejc0jZox0ja 7h9GMJJxeZhemdoDlD9HOfxr5SS/eg2Ldcun9EjIRfkb9viNGuVK1uRZaq4YTqD2UEOr AF/09r9tjZiBYvk/+UwfGZRlPvWkIY+6ZJZClfiuKogC9Kiq5zOulCw+XBQeJKovz93V qsUw== X-Forwarded-Encrypted: i=1; AJvYcCWr4gXSdFpwQek0nbzjm5WAeNi5ni7jxYa0CiFnX2mOQGTOUIK3mPvnqWCYRukfkt1n09rHGO99zRg2UuM=@vger.kernel.org X-Gm-Message-State: AOJu0Yyou5eHzlhDrOIhpDKrP3pWQ40aoAPhdpn2mPIvgu5QoEqmb/gH DwuDKdIm8uofFWhzM2/g8g8HUy8zw0VrD2YxiolTRM/zZSVpEBoz6tny X-Gm-Gg: AZuq6aKxKCnRDRzjhXsJJRzEzr4j57Gjf1WGSymAzSZ8ZDCHQPq2J15aQtOawxHzUQK g10QNQ1t6A4Z7/8EbxaHcHtdzq9ueAzCjuPQ1kJXPIqBXbOc+5Q8q1qm7E5DfKxLyNkUIX+BL23 wIWxmIujrL7JiARlKc2WqA96l2OrKp8FTYJwuly62B4W4R6VSeWh4ceKoMK42qbf9QsjaAtoQMy njQ3bU6gYnGXaEUNh2ieCWqIhvD0jVm0y04FRB0CP+QH3FnmF6eHDwNtJ+KRsF94fzYlZIjqFak tiABj/QAX9PhxgH6m+9fW5+wZqh6zu7eymdimn57QmE4upMpy5kmBbdQ0aIE8tGdwknYWRleut9 iXlVLDA+d2giAV17hlg9uY0ulpNmHeRB/w2UMls+ltKAsk8Kl/fvlqVcqr8ER9Dv9QvCmiCz4ZU 1ufw7lBniUGpQcOnaSiiykoA== X-Received: by 2002:a05:690c:d8d:b0:794:7be0:8217 with SMTP id 00721157ae682-79803d031ffmr1521947b3.52.1771438272580; Wed, 18 Feb 2026 10:11:12 -0800 (PST) Received: from localhost ([2a03:2880:25ff:5f::]) by smtp.gmail.com with ESMTPSA id 00721157ae682-7966c254d5asm129169257b3.43.2026.02.18.10.11.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 Feb 2026 10:11:12 -0800 (PST) From: Bobby Eshleman Date: Wed, 18 Feb 2026 10:10:37 -0800 Subject: [PATCH net v2 2/3] vsock: lock down child_ns_mode as write-once Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20260218-vsock-ns-write-once-v2-2-19e4c50d509a@meta.com> References: <20260218-vsock-ns-write-once-v2-0-19e4c50d509a@meta.com> In-Reply-To: <20260218-vsock-ns-write-once-v2-0-19e4c50d509a@meta.com> To: Stefano Garzarella , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Stefan Hajnoczi , Shuah Khan , Bobby Eshleman , "Michael S. Tsirkin" , Jonathan Corbet , Shuah Khan Cc: virtualization@lists.linux.dev, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-doc@vger.kernel.org, Daan De Meyer X-Mailer: b4 0.14.3 From: Bobby Eshleman Two administrator processes may race when setting child_ns_mode as one process sets child_ns_mode to "local" and then creates a namespace, but another process changes child_ns_mode to "global" between the write and the namespace creation. The first process ends up with a namespace in "global" mode instead of "local". While this can be detected after the fact by reading ns_mode and retrying, it is fragile and error-prone. Make child_ns_mode write-once so that a namespace manager can set it once and be sure it won't change. Writing a different value after the first write returns -EBUSY. This applies to all namespaces, including init_net, where an init process can write "local" to lock all future namespaces into local mode. Fixes: eafb64f40ca4 ("vsock: add netns to vsock core") Signed-off-by: Bobby Eshleman Suggested-by: Daan De Meyer Suggested-by: Stefano Garzarella --- include/net/af_vsock.h | 20 +++++++++++++++++--- include/net/netns/vsock.h | 9 ++++++++- net/vmw_vsock/af_vsock.c | 15 ++++++++++----- 3 files changed, 35 insertions(+), 9 deletions(-) diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h index d3ff48a2fbe0..9bd42147626d 100644 --- a/include/net/af_vsock.h +++ b/include/net/af_vsock.h @@ -276,15 +276,29 @@ static inline bool vsock_net_mode_global(struct vsock= _sock *vsk) return vsock_net_mode(sock_net(sk_vsock(vsk))) =3D=3D VSOCK_NET_MODE_GLOB= AL; } =20 -static inline void vsock_net_set_child_mode(struct net *net, +static inline bool vsock_net_set_child_mode(struct net *net, enum vsock_net_mode mode) { - WRITE_ONCE(net->vsock.child_ns_mode, mode); + int locked =3D mode + VSOCK_NET_MODE_LOCKED; + int cur; + + cur =3D READ_ONCE(net->vsock.child_ns_mode); + if (cur =3D=3D locked) + return true; + if (cur >=3D VSOCK_NET_MODE_LOCKED) + return false; + + if (try_cmpxchg(&net->vsock.child_ns_mode, &cur, locked)) + return true; + + return cur =3D=3D locked; } =20 static inline enum vsock_net_mode vsock_net_child_mode(struct net *net) { - return READ_ONCE(net->vsock.child_ns_mode); + int mode =3D READ_ONCE(net->vsock.child_ns_mode); + + return mode & (VSOCK_NET_MODE_LOCKED - 1); } =20 /* Return true if two namespaces pass the mode rules. Otherwise, return fa= lse. diff --git a/include/net/netns/vsock.h b/include/net/netns/vsock.h index b34d69a22fa8..d20ab6269342 100644 --- a/include/net/netns/vsock.h +++ b/include/net/netns/vsock.h @@ -7,6 +7,7 @@ enum vsock_net_mode { VSOCK_NET_MODE_GLOBAL, VSOCK_NET_MODE_LOCAL, + VSOCK_NET_MODE_LOCKED, }; =20 struct netns_vsock { @@ -16,6 +17,12 @@ struct netns_vsock { u32 port; =20 enum vsock_net_mode mode; - enum vsock_net_mode child_ns_mode; + + /* 0 (GLOBAL) + * 1 (LOCAL) + * 2 (GLOBAL + LOCKED) + * 3 (LOCAL + LOCKED) + */ + int child_ns_mode; }; #endif /* __NET_NET_NAMESPACE_VSOCK_H */ diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c index 9880756d9eff..50044a838c89 100644 --- a/net/vmw_vsock/af_vsock.c +++ b/net/vmw_vsock/af_vsock.c @@ -90,16 +90,20 @@ * * - /proc/sys/net/vsock/ns_mode (read-only) reports the current namespa= ce's * mode, which is set at namespace creation and immutable thereafter. - * - /proc/sys/net/vsock/child_ns_mode (writable) controls what mode fut= ure + * - /proc/sys/net/vsock/child_ns_mode (write-once) controls what mode f= uture * child namespaces will inherit when created. The initial value match= es * the namespace's own ns_mode. * * Changing child_ns_mode only affects newly created namespaces, not the * current namespace or existing children. A "local" namespace cannot set - * child_ns_mode to "global". At namespace creation, ns_mode is inherited - * from the parent's child_ns_mode. + * child_ns_mode to "global". child_ns_mode is write-once, so that it ma= y be + * configured and locked down by a namespace manager. Writing a different + * value after the first write returns -EBUSY. At namespace creation, ns= _mode + * is inherited from the parent's child_ns_mode. * - * The init_net mode is "global" and cannot be modified. + * The init_net mode is "global" and cannot be modified. The init_net + * child_ns_mode is also write-once, so an init process (e.g. systemd) c= an + * set it to "local" to ensure all new namespaces inherit local mode. * * The modes affect the allocation and accessibility of CIDs as follows: * @@ -2853,7 +2857,8 @@ static int vsock_net_child_mode_string(const struct c= tl_table *table, int write, new_mode =3D=3D VSOCK_NET_MODE_GLOBAL) return -EPERM; =20 - vsock_net_set_child_mode(net, new_mode); + if (!vsock_net_set_child_mode(net, new_mode)) + return -EBUSY; } =20 return 0; --=20 2.47.3