From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 E4E8B33343C for ; Thu, 19 Feb 2026 10:35:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771497361; cv=none; b=aIuGEZ/99e0d9GarlgKvUb0vvZ3ULGNo/eJQUJqAuDBbnr9YfNNVn4zl0ENieKGCa49MJRpcG/N8aJrokEixECQDyZba1JALFNDPyYLZI0/suKlxEw2YxCUN3shsiAqvkZHz0f6MSGg6kKEk/10lUL/ugMpRL90tmr2Wgc21M3s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771497361; c=relaxed/simple; bh=eTIUgii0YmaylqM4iVI/YNV+QeRj+PKWD6nx1b8Mkvw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=PCp8mPpe0eS7wPookR29SuJTQFQH04xPADuIqcF4z/Q0l/uPj0C0zgwAF+0hHwNIt9FsblNbCiGVx81Lb9VRpkZ3WpgVsRSFOqL0BSpqfFOssBTIaHsGPJrSMoEKy7FXXk+eEeFcqQgYb0MaGtjbzD2enm8jPJMimhuGKHqlc5c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=OXKf2zg5; dkim=pass (2048-bit key) header.d=redhat.com header.i=@redhat.com header.b=LFmJ51Ag; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="OXKf2zg5"; dkim=pass (2048-bit key) header.d=redhat.com header.i=@redhat.com header.b="LFmJ51Ag" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1771497359; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=bEmwL6W5pHYJ3lHWdTPnl0swpUbILrk1rjryh3uy/K8=; b=OXKf2zg56PtHajqALLGzTwe/N1/yh6dxNZqFwRrNL3f3cpWsRhOXZ13eE2LBP1b6yZ60yZ QNomLQ2UJJ2TtPjMAwrasnJQFA2BnCtdloOKWsfO5ibL1DnwGetGxlGmJgOF30igVL9B1S JiqW76+jK0yNEydDnz9UAdGevrMYVlw= Received: from mail-wm1-f71.google.com (mail-wm1-f71.google.com [209.85.128.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-612-b963crPnMjeDuE7iBx9hSA-1; Thu, 19 Feb 2026 05:35:57 -0500 X-MC-Unique: b963crPnMjeDuE7iBx9hSA-1 X-Mimecast-MFC-AGG-ID: b963crPnMjeDuE7iBx9hSA_1771497356 Received: by mail-wm1-f71.google.com with SMTP id 5b1f17b1804b1-4837907ec88so13556035e9.0 for ; Thu, 19 Feb 2026 02:35:57 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=google; t=1771497356; x=1772102156; darn=vger.kernel.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=bEmwL6W5pHYJ3lHWdTPnl0swpUbILrk1rjryh3uy/K8=; b=LFmJ51AgMZJLQ/X/IJzQWw1aT1UlonUOAdOjiltfQuIh/vGvbz9f01HzwYo/m2Y0bx pPWm+GO7wXs1ATqA04WPJgX09vael9CkPQCUykih93awRRIIROY5xixZ9luelzyYOvx5 DxGX8aubBmLFDK/ejPlrp3X+eidiXY2DnsMLarDa9+NEza4+m6+brJAhrMajTr1R1XjV XB2beViBcLiJlZiyot87qxlCXC1uKta9G/AatzFsulHPE/cKY5q2djUEKg8Ij2K1F5HY s1xTwYQTrQzDNBQWKsP98Zotu1LqcZ97iUyORUI1xWcDfgPxUMyqXzaQCbE6lJqVyiIo mXWQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1771497356; x=1772102156; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-gg:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=bEmwL6W5pHYJ3lHWdTPnl0swpUbILrk1rjryh3uy/K8=; b=k88JSKPj1Zyky6h/PrMYJU6R8zL/fy5nwFpy1igLMA+icKY+noKec/8hYx2d2fcJAZ WbebmOvFWN27uTeKhVgJyuZ0yqUmNzX7+Y/m4BD9M2L6iBKy72phtqLR5IhLuqdBSrCT rdiXALNQz+sIJLQ4T1sEEU7Sl3sWIZxrFXbmo7CVvbi63xeTFpXbWLhD2m9vsIa7d2n9 hYBF+VKBcxFHJafa/d+x9X5WC15tbDNYTciDf5ZvpXfaZZ8CYqiF0tJXQ5P+KDAB/+6j u8kRsf+yEmLbUPc3O9NQXNbkACLCs8+FKnADWv+sceHaY1lIRSL8Py94c6YyJHcWYzuV SF/w== X-Forwarded-Encrypted: i=1; AJvYcCWoPgmMjfyXxBxLG28A2q1gs6DZtuJaXK8CgaRsfn4A6tdLUflL7SXifKgTPNwdO9BXivTz5tM=@vger.kernel.org X-Gm-Message-State: AOJu0YzGIUI2tBNmQMB4MbSr1D/yhZgLIe2bob0MPz1oEe2qkI/uddiD NDhBkHMLVFFhXR6KLQKUfhzcaGa8r/j+fQCCDuayFZcOy4QSKRKwd69D0qumXmd2dg8+CGNy1PX ze7h4LcSMqUDE0V+8Io/39eJKxaSwemvzaLXJoWK0z4DyhlJDTUBdFd7NBA== X-Gm-Gg: AZuq6aJkGiHIXM+2ZwtOpPFzaKAa708rLtOdj4DBERqZllvsQgifzMQ1I1Tz7WNnmoF al5ARIz1vh/VBDp1dl4lzmww9ozeEKgTL9WKDuzCe/LFxD/qCsfaT//vl6OgJGMlui2anwWKH7X fg+CFzPCCkBZgXhT4qCGpun/xOCtpt84TQWAXeHEUCECCCL19tnHJKqGJbV5bo9VpWzEJPvPYIi UzshL5Vsl1BSTsJS8kakM5sy6QWjUCJHsM89KogHN+bfo4IXHZUBOxjMTBR0afQDfVaU4Jxaves WvwsDmVuBjT1M0FLrdpuyw3QZgsie4bNY7H8MoL4DYBFzkfAyrqHglunQE+LqM7tBEQ6A2OG8Z9 nUs1zsdWVfkVHNA6GQ7M/xRF8ZaUefXbmDQIgoY4a/PccCz6phJauMAFb26pON9hOasv/6jk= X-Received: by 2002:a05:600c:46cf:b0:483:709e:f238 with SMTP id 5b1f17b1804b1-48373a58867mr322370695e9.29.1771497356199; Thu, 19 Feb 2026 02:35:56 -0800 (PST) X-Received: by 2002:a05:600c:46cf:b0:483:709e:f238 with SMTP id 5b1f17b1804b1-48373a58867mr322370165e9.29.1771497355597; Thu, 19 Feb 2026 02:35:55 -0800 (PST) Received: from sgarzare-redhat (host-82-53-134-58.retail.telecomitalia.it. [82.53.134.58]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4834d8334a8sm680068285e9.12.2026.02.19.02.35.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 19 Feb 2026 02:35:54 -0800 (PST) Date: Thu, 19 Feb 2026 11:35:52 +0100 From: Stefano Garzarella To: Bobby Eshleman Cc: "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Stefan Hajnoczi , Shuah Khan , Bobby Eshleman , "Michael S. Tsirkin" , Jonathan Corbet , Shuah Khan , 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 Subject: Re: [PATCH net v2 2/3] vsock: lock down child_ns_mode as write-once Message-ID: References: <20260218-vsock-ns-write-once-v2-0-19e4c50d509a@meta.com> <20260218-vsock-ns-write-once-v2-2-19e4c50d509a@meta.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20260218-vsock-ns-write-once-v2-2-19e4c50d509a@meta.com> On Wed, Feb 18, 2026 at 10:10:37AM -0800, Bobby Eshleman wrote: >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 nit: usually the S-o-b of the author is the last when sending a patch. >--- > 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))) == VSOCK_NET_MODE_GLOBAL; > } > >-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 = mode + VSOCK_NET_MODE_LOCKED; >+ int cur; >+ >+ cur = READ_ONCE(net->vsock.child_ns_mode); >+ if (cur == locked) >+ return true; >+ if (cur >= VSOCK_NET_MODE_LOCKED) >+ return false; >+ >+ if (try_cmpxchg(&net->vsock.child_ns_mode, &cur, locked)) >+ return true; >+ >+ return cur == locked; Sorry, it took me a while to get it entirely :-( This overcomplication is exactly what I wanted to avoid when I proposed the change in v1: https://lore.kernel.org/netdev/aZWUmbiH11Eh3Y4v@sgarzare-redhat/ > } > > static inline enum vsock_net_mode vsock_net_child_mode(struct net *net) > { >- return READ_ONCE(net->vsock.child_ns_mode); >+ int mode = READ_ONCE(net->vsock.child_ns_mode); >+ >+ return mode & (VSOCK_NET_MODE_LOCKED - 1); This is working just because VSOCK_NET_MODE_LOCKED == 2, so IMO this should at least set as value in the enum and documented on top of vsock_net_mode. > } > > /* Return true if two namespaces pass the mode rules. Otherwise, return false. >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, This is not really a mode, so IMO should not be part of `enum vsock_net_mode`. If you really want it, maybe we can add both VSOCK_NET_MODE_GLOBAL_LOCKED and VSOCK_NET_MODE_LOCAL_LOCKED, which can be less error prone if we will touch this enum one day. > }; > > struct netns_vsock { >@@ -16,6 +17,12 @@ struct netns_vsock { > u32 port; > > 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; Sorry, I don't like this too much, since it seems too complicated to read and to maintain, If we really want to use just one variable, maybe we can use -1 as UNSET for child_ns_mode. If it is UNSET, vsock_net_child_mode() can just return `mode` since it's the default that we also documented, if it's set, it means that is locked with the value specified. Maybe with code is easier, I mean something like this: diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h index d3ff48a2fbe0..fcd5b538df35 100644 --- a/include/net/af_vsock.h +++ b/include/net/af_vsock.h @@ -276,15 +276,25 @@ static inline bool vsock_net_mode_global(struct vsock_sock *vsk) return vsock_net_mode(sock_net(sk_vsock(vsk))) == VSOCK_NET_MODE_GLOBAL; } -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 old = VSOCK_NET_CHILD_NS_UNSET; + + if (try_cmpxchg(&net->vsock.child_ns_mode, &old, mode)) + return true; + + return old == mode; } static inline enum vsock_net_mode vsock_net_child_mode(struct net *net) { - return READ_ONCE(net->vsock.child_ns_mode); + int mode = READ_ONCE(net->vsock.child_ns_mode); + + if (mode == VSOCK_NET_CHILD_NS_UNSET) + return net->vsock.mode; + + return mode; } /* Return true if two namespaces pass the mode rules. Otherwise, return false. diff --git a/include/net/netns/vsock.h b/include/net/netns/vsock.h index b34d69a22fa8..bf52baf7d7a7 100644 --- a/include/net/netns/vsock.h +++ b/include/net/netns/vsock.h @@ -9,6 +9,8 @@ enum vsock_net_mode { VSOCK_NET_MODE_LOCAL, }; +#define VSOCK_NET_CHILD_NS_UNSET (-1) + struct netns_vsock { struct ctl_table_header *sysctl_hdr; @@ -16,6 +18,13 @@ struct netns_vsock { u32 port; enum vsock_net_mode mode; - enum vsock_net_mode child_ns_mode; + + /* Write-once child namespace mode, must be initialized to + * VSOCK_NET_CHILD_NS_UNSET. Transitions once from UNSET to a + * vsock_net_mode value via try_cmpxchg on first sysctl write. + * While UNSET, vsock_net_child_mode() returns the namespace's + * own mode since it's the default. + */ + 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..f0cb7c6a8212 100644 --- a/net/vmw_vsock/af_vsock.c +++ b/net/vmw_vsock/af_vsock.c @@ -2853,7 +2853,8 @@ static int vsock_net_child_mode_string(const struct ctl_table *table, int write, new_mode == VSOCK_NET_MODE_GLOBAL) return -EPERM; - vsock_net_set_child_mode(net, new_mode); + if (!vsock_net_set_child_mode(net, new_mode)) + return -EBUSY; } return 0; @@ -2922,7 +2923,7 @@ static void vsock_net_init(struct net *net) else net->vsock.mode = vsock_net_child_mode(current->nsproxy->net_ns); - net->vsock.child_ns_mode = net->vsock.mode; + net->vsock.child_ns_mode = VSOCK_NET_CHILD_NS_UNSET; } static __net_init int vsock_sysctl_init_net(struct net *net) If you like it, please add my Co-developed-by and S-o-b. BTW, let's discuss here more about it and agree before sending a new version, so this should also allow other to comment eventually. Thanks, Stefano > }; > #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 namespace's > * mode, which is set at namespace creation and immutable thereafter. >- * - /proc/sys/net/vsock/child_ns_mode (writable) controls what mode future >+ * - /proc/sys/net/vsock/child_ns_mode (write-once) controls what mode future > * child namespaces will inherit when created. The initial value matches > * 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 may 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) can >+ * 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 ctl_table *table, int write, > new_mode == VSOCK_NET_MODE_GLOBAL) > return -EPERM; > >- vsock_net_set_child_mode(net, new_mode); >+ if (!vsock_net_set_child_mode(net, new_mode)) >+ return -EBUSY; > } > > return 0; > >-- >2.47.3 >