From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 D0C1741B341 for ; Wed, 21 Jan 2026 12:10:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768997443; cv=none; b=ljTBBeWLIPx80tXaunKCbvSbYXk3oaCCxFdGe/mvjvmTk8tTcDBWAHmMK8Dj2gq+na2OZ3cdRcE4GYWOCn8QZXe8hhgzk9sV4sgH/89vAPDTOtCl3+QVD/JxN23hndDrYTzLvGtdrJ7VjykDdU4Z/Y7atd7fpXNZ4jXyTzhoDA4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768997443; c=relaxed/simple; bh=GZ3GsuG+E3Qr6/RqofEs4s8euNMw69P/GSTuShgkEDo=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=hH/zsVTZPtu+2htiJuPXV1PFUtFOOB5uGL4IiMTY20YVj+WMP4+30xIQgOR0zLRzZPyVVuaH0DRnM8seeSvSGs+zI856ac8uggB/4fcEOknlk0gcDE1ABhWXBa4fJveFkF49pM8g43AjN/6QKAXH6I7vryoUWweeSx9KEoxatU8= 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=XBblhhci; dkim=pass (2048-bit key) header.d=redhat.com header.i=@redhat.com header.b=Yk/plsDL; arc=none smtp.client-ip=170.10.129.124 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="XBblhhci"; dkim=pass (2048-bit key) header.d=redhat.com header.i=@redhat.com header.b="Yk/plsDL" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1768997433; 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=vvEBWBLr1X14L0avrzDsdXo8a3nnKtSJtim3XAg072w=; b=XBblhhcipS6CBp0PsHeddJ5djqSj78auvENTW0NrVlsm4ivrA+4oLWrhFfxf1gcWi6/iGl ab2ALUtBtEbVRknHxN/346x9quwPafFUfwi5WiyqGedkif4z7fUp1m1N7aCfAjg3Ayv4pr 4ne1WviKmg/GU8bww7wZ+S4FOKD73gQ= Received: from mail-wm1-f72.google.com (mail-wm1-f72.google.com [209.85.128.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-49-z4C5RJR1NWuw5Jfkm-LTKw-1; Wed, 21 Jan 2026 07:10:32 -0500 X-MC-Unique: z4C5RJR1NWuw5Jfkm-LTKw-1 X-Mimecast-MFC-AGG-ID: z4C5RJR1NWuw5Jfkm-LTKw_1768997431 Received: by mail-wm1-f72.google.com with SMTP id 5b1f17b1804b1-47d62cc05daso46893225e9.3 for ; Wed, 21 Jan 2026 04:10:32 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=google; t=1768997431; x=1769602231; 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=vvEBWBLr1X14L0avrzDsdXo8a3nnKtSJtim3XAg072w=; b=Yk/plsDLRsXjspA2NU+UhMAWnxvtMa4C1QG66a6QwipcN23tLPLzNjLlIzZDuPiHWb fiFcfOOagmr4dVqGNQEw1rAEV4IAzly4t92GWRJm1KS7w34YARnGc9bxGgFTCVxQcOtt zBixAiUtWhQhLfy3kXXPvzwoIl0evUEVjXnHZ1RfL+kTpmNMJfgAwNhcrEcG2nJbeR2q LbYKO0JmNCHzKnycIIb1TLtbIbLaGfkQQG1LaIEpyaYXTFwVdYcP2PseyUbQByfCmOcM pgQa0Bo1j2WLVy3oBu4USNq1BOIBzPlsy3DwtM5AUdSdb2XwWf05HxRF5j4DK/9GCyou QaFQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1768997431; x=1769602231; 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=vvEBWBLr1X14L0avrzDsdXo8a3nnKtSJtim3XAg072w=; b=E4ORwfxmQh1LDTyZAP3WFo/23kqiBjSkK9YWqRA1ol9xrsRcJEVoIfPDsJ0AsvwNQM jopcSe+2abg+2ZHj90DbpNu6oxvCHHp1UeAa1tYe+yzx1JpOlW0Wv2cXRYD2NAl3XIAF m8E9wcIYqguJouVQvOuUuR6m+fhLzNFf/amiNxBc275Ce5mkyYy3Kmyk4T6TzN6Th4QU QIc3osIWHwp9RnEcfpfLNaJR6s9KXCoKQqUnOaUwH54QxirJJrgVq4V/4nN6tAU/AQ/z VS3I7a6qpo6fgRxrHW/c01n/h7J3eHXQqWivAQf0MmbKl/YejGDZlio5tpkCyBATrJwj 4+mQ== X-Gm-Message-State: AOJu0Yw1m4j7dXXtVOQeNV+H6OptzHbUdRyRO8m3F8voWpwe870Sr6j4 ho8ACCvnGzWswmZZWwxvEVDBFNgKRHUWutaAigoih0QR/y227uacD09R/VtGDTbVhpwep13jAOC NR+XCyfqicVmhbWpps4xIt7GvRjyzIzpILEEJrizjjpkxFT4bQLR/poOOlw== X-Gm-Gg: AZuq6aLjzE4mLH1UDHgFJTm2AdkV3JBKLjLzCOGNHK5zv1PYak3+fQZNpSn6UdbZQaj ST+yiLBOrcb0GTzExjhxs+aem324+2yax0M07JfBslvtBn1tQHGjvhvKEGQajCaCniDKrBetQJP zOhmwmf8/I+PDc8dEKNn8upJIW7zfNxFVg3+lOBzL6YjoCrbmea8XITXckNdry+DqvFWwQVmSpR wFI5oyPx4bek66gzJBdcPRF/YjeYFWstHV1h+j/0xuzcEQcGtVtUJcVEafxfrf+gYkaAWF9eHxh IirQOQfKyk1idrLNm2l4tu7s/5LsNGCRB5oZ1TVaAkRbJ5dZDqQ6JyaqhlqKcu3PQmKhO5mnXb7 rLLoAP4l+tEanyGE= X-Received: by 2002:a05:600c:81c5:b0:46e:4e6d:79f4 with SMTP id 5b1f17b1804b1-4803e7a529emr72395205e9.15.1768997431360; Wed, 21 Jan 2026 04:10:31 -0800 (PST) X-Received: by 2002:a05:600c:81c5:b0:46e:4e6d:79f4 with SMTP id 5b1f17b1804b1-4803e7a529emr72394825e9.15.1768997430942; Wed, 21 Jan 2026 04:10:30 -0800 (PST) Received: from leonardi-redhat ([176.206.16.134]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48043617b81sm38961085e9.0.2026.01.21.04.10.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 21 Jan 2026 04:10:30 -0800 (PST) Date: Wed, 21 Jan 2026 13:10:28 +0100 From: Luigi Leonardi To: Stefano Garzarella Cc: netdev@vger.kernel.org, Simon Horman , Eric Dumazet , "Michael S. Tsirkin" , Arseniy Krasnov , "David S. Miller" , virtualization@lists.linux.dev, Paolo Abeni , Jakub Kicinski , Stefan Hajnoczi , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Claudio Imbrenda , Jason Wang , Xuan Zhuo , Eugenio =?utf-8?B?UMOpcmV6?= , Asias He , Melbin K Mathew Subject: Re: [PATCH net v6 3/4] vsock/virtio: cap TX credit to local buffer size Message-ID: References: <20260121093628.9941-1-sgarzare@redhat.com> <20260121093628.9941-4-sgarzare@redhat.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: <20260121093628.9941-4-sgarzare@redhat.com> On Wed, Jan 21, 2026 at 10:36:27AM +0100, Stefano Garzarella wrote: >From: Melbin K Mathew > >The virtio transports derives its TX credit directly from peer_buf_alloc, >which is set from the remote endpoint's SO_VM_SOCKETS_BUFFER_SIZE value. > >On the host side this means that the amount of data we are willing to >queue for a connection is scaled by a guest-chosen buffer size, rather >than the host's own vsock configuration. A malicious guest can advertise >a large buffer and read slowly, causing the host to allocate a >correspondingly large amount of sk_buff memory. >The same thing would happen in the guest with a malicious host, since >virtio transports share the same code base. > >Introduce a small helper, virtio_transport_tx_buf_size(), that >returns min(peer_buf_alloc, buf_alloc), and use it wherever we consume >peer_buf_alloc. > >This ensures the effective TX window is bounded by both the peer's >advertised buffer and our own buf_alloc (already clamped to >buffer_max_size via SO_VM_SOCKETS_BUFFER_MAX_SIZE), so a remote peer >cannot force the other to queue more data than allowed by its own >vsock settings. > >On an unpatched Ubuntu 22.04 host (~64 GiB RAM), running a PoC with >32 guest vsock connections advertising 2 GiB each and reading slowly >drove Slab/SUnreclaim from ~0.5 GiB to ~57 GiB; the system only >recovered after killing the QEMU process. That said, if QEMU memory is >limited with cgroups, the maximum memory used will be limited. > >With this patch applied: > > Before: > MemFree: ~61.6 GiB > Slab: ~142 MiB > SUnreclaim: ~117 MiB > > After 32 high-credit connections: > MemFree: ~61.5 GiB > Slab: ~178 MiB > SUnreclaim: ~152 MiB > >Only ~35 MiB increase in Slab/SUnreclaim, no host OOM, and the guest >remains responsive. > >Compatibility with non-virtio transports: > > - VMCI uses the AF_VSOCK buffer knobs to size its queue pairs per > socket based on the local vsk->buffer_* values; the remote side > cannot enlarge those queues beyond what the local endpoint > configured. > > - Hyper-V's vsock transport uses fixed-size VMBus ring buffers and > an MTU bound; there is no peer-controlled credit field comparable > to peer_buf_alloc, and the remote endpoint cannot drive in-flight > kernel memory above those ring sizes. > > - The loopback path reuses virtio_transport_common.c, so it > naturally follows the same semantics as the virtio transport. > >This change is limited to virtio_transport_common.c and thus affects >virtio-vsock, vhost-vsock, and loopback, bringing them in line with the >"remote window intersected with local policy" behaviour that VMCI and >Hyper-V already effectively have. > >Fixes: 06a8fc78367d ("VSOCK: Introduce virtio_vsock_common.ko") >Suggested-by: Stefano Garzarella >Signed-off-by: Melbin K Mathew >[Stefano: small adjustments after changing the previous patch] >[Stefano: tweak the commit message] >Signed-off-by: Stefano Garzarella >--- > net/vmw_vsock/virtio_transport_common.c | 14 ++++++++++++-- > 1 file changed, 12 insertions(+), 2 deletions(-) > >diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c >index 6175124d63d3..d3e26025ef58 100644 >--- a/net/vmw_vsock/virtio_transport_common.c >+++ b/net/vmw_vsock/virtio_transport_common.c >@@ -821,6 +821,15 @@ virtio_transport_seqpacket_dequeue(struct vsock_sock *vsk, > } > EXPORT_SYMBOL_GPL(virtio_transport_seqpacket_dequeue); > >+static u32 virtio_transport_tx_buf_size(struct virtio_vsock_sock *vvs) >+{ >+ /* The peer advertises its receive buffer via peer_buf_alloc, but we >+ * cap it to our local buf_alloc so a remote peer cannot force us to >+ * queue more data than our own buffer configuration allows. >+ */ >+ return min(vvs->peer_buf_alloc, vvs->buf_alloc); >+} >+ > int > virtio_transport_seqpacket_enqueue(struct vsock_sock *vsk, > struct msghdr *msg, >@@ -830,7 +839,7 @@ virtio_transport_seqpacket_enqueue(struct vsock_sock *vsk, > > spin_lock_bh(&vvs->tx_lock); > >- if (len > vvs->peer_buf_alloc) { >+ if (len > virtio_transport_tx_buf_size(vvs)) { > spin_unlock_bh(&vvs->tx_lock); > return -EMSGSIZE; > } >@@ -884,7 +893,8 @@ static s64 virtio_transport_has_space(struct virtio_vsock_sock *vvs) > * we have bytes in flight (tx_cnt - peer_fwd_cnt), the subtraction > * does not underflow. > */ >- bytes = (s64)vvs->peer_buf_alloc - (vvs->tx_cnt - vvs->peer_fwd_cnt); >+ bytes = (s64)virtio_transport_tx_buf_size(vvs) - >+ (vvs->tx_cnt - vvs->peer_fwd_cnt); > if (bytes < 0) > bytes = 0; > >-- >2.52.0 > LGTM! Reviewed-by: Luigi Leonardi