From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-lf1-f54.google.com (mail-lf1-f54.google.com [209.85.167.54]) (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 5BD3B1624DF for ; Wed, 10 Dec 2025 13:33:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.167.54 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765373606; cv=none; b=VlhtkFuYyZCmvr0hA+UznTuqLB2zw7fsqVafXTZlBUfXSn+ZXUG4n6Jx5lLBxxWzArm+RPXPvebFMExOTPK3H5GRHlKY6fiWTmVAwBNylQgoZxYnLsVS+FFYjYh/txyDNNRva/16jeNDQg0TwppryZrAiwCPwlxrmCfujCZkg8M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765373606; c=relaxed/simple; bh=0wLH31HDwfSTe/1EuiWHtYsukRblUE1QRCxb3uKciDA=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=pRiIoX7R8gfbMq3m6YZ3jXOS7LTmCIPLLWYEAdRbF6Rn0+nUscMUvgGuHlbFUwLDGoD4v9X8xAB5/4RSKPlqCcSjlkLieF4p5N4WpV3nELe71Snr66mKvhg1zuG27Mt95d6EwlOIVpfHKkNzIBbRG+GRN1ngLzwpOmXrSl8F9Jo= 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=R1Hm7q0r; arc=none smtp.client-ip=209.85.167.54 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="R1Hm7q0r" Received: by mail-lf1-f54.google.com with SMTP id 2adb3069b0e04-5957e017378so8680886e87.3 for ; Wed, 10 Dec 2025 05:33:24 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1765373602; x=1765978402; darn=lists.linux.dev; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=oD5ipYc8BirTwTUNyp9GQ08Nz/lO30YuP7q1nZr2KbU=; b=R1Hm7q0rCqLiT7tFHLuN3N1ERnqOaVgvVHGzvRhzmFVFKGoYGSfeuVZhMA3K/ZwzB4 kyb+CbuhTfLEHxpJDUKdl/5mvvRwRLTQZGQ+N8t7PghZEm5RfEyKHEY5UEYfxwmjFAmN QKRBu6IKaoJzvM87GF+Sy3n0c1JRuBLLE7w2rY+svFSRz5AUehQUEfx4Jw9cQN7cIWUe 4moabVnfmTIwgyNgjhqKvn9aa1YxttZTPPNh0/UzZ5GJugopbMFvtppGBhKVKUYptkDj sEk2i0/8c10rGm36Docfv1iagR7Q0ZhdJAY/kA17uO/AH+xaxuvlgiGoNCzmDoDAkgSl Hu+w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1765373602; x=1765978402; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-gg:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=oD5ipYc8BirTwTUNyp9GQ08Nz/lO30YuP7q1nZr2KbU=; b=HeJDcGfL1E/GtGjuoblxZOjh3ypr8d42aCWlNLYpbBG5ABPpOd3oH74GrMwhHza+oQ 65bjAGyWsYUcH1lGowqBoPj63VlgJ9rR+YxbUJVdW3QbZbVKSoabTiiOw6lv4VrBbQxW w2Y4CJNOXcqpyWQCxAitAybfyQ15eQVmJcZIdmh9znccSmxE8QkfGvk4iLPdGSV4UTfO 960Klnc9tg5k4fUPm/hBvFbvqArWjhP4SgimOEKVjwnD8fRpvs1QuqCxydvx1xmzTGDF h9Zw5d34kW5tlNdiM4yTXy8AtYObk/1B6APHr/z2mVBlcXYAVE/4WeJFxOx5PA/2Z9Aa 6SRQ== X-Gm-Message-State: AOJu0YzuEutZrOcJnpHaIa+PrMoY4cF/DCea+6NiA8RZ1F0nrSkXasbg e0rkrKvLdXFnxwRIcWVlplttx/57Exk1OYXUkCGkMfWaSXntuEC9EwHK X-Gm-Gg: AY/fxX5bzJ5ywejq7zCZLQnY57tQDZgCiWWhdLmn6WsXXDOiQeKrhhgv8GjPL0N9EoQ tfGMTQJkOjGxIzVw7tCBkMut4uUFWBsOpHzXvi02ffjL37bL+wnfdu1W39iHOwWZDZ7DioH1UZ1 EnTOxLKyo0gdHtAy70jzmU4kudvFYoucNbQXJnRG3smRyvb/SzLf/8/lM3keVk/eYfqpiwLl4zu NEJn6PqyjuIFGpeLrC3Ohy9TvXyqv+cm3gV3l11h//fB92xrYSq7S8OvNGloKebmDv0fHuAKb8z 5+DEtr8ErA1bCTNAfFLBFCmIBDxv/RQpbX+gqKACrcqdJMAbIVEsRM/tPZW/NUsgwEgYIUUQuNU vC15XuKn74Y34BM2FLQYfbcrhAF7OE0dVbUmC96ZTnbjXdpb2VZEmvITVOCZrlPrp1iNG/4Dfn3 bDUWwAinPdfNw= X-Google-Smtp-Source: AGHT+IGuUo6ZoxmOLPJELy4E+MQsRaQCeY8UlKN8xDwSV5aN/WHR1k1qW9H8XravEGuc7+/9yStW0A== X-Received: by 2002:a05:6512:3d8c:b0:595:9d90:5dc6 with SMTP id 2adb3069b0e04-598ee4e6446mr990906e87.19.1765373602129; Wed, 10 Dec 2025 05:33:22 -0800 (PST) Received: from Ubuntu-2204-jammy-amd64-base.. ([2a01:4f9:6a:4e9f::2]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-597d7c1e2acsm6473621e87.61.2025.12.10.05.33.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 10 Dec 2025 05:33:21 -0800 (PST) From: Melbin K Mathew To: netdev@vger.kernel.org Cc: virtualization@lists.linux.dev, linux-kernel@vger.kernel.org, sgarzare@redhat.com, stefanha@redhat.com, mst@redhat.com, jasowang@redhat.com, Melbin K Mathew Subject: [PATCH net] vsock/virtio: cap TX credit to local buffer size Date: Wed, 10 Dec 2025 14:32:59 +0100 Message-Id: <20251210133259.16238-1-mlbnkm1@gmail.com> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The virtio vsock transport currently 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. Introduce a small helper, virtio_transport_peer_buf_alloc(), that returns min(peer_buf_alloc, buf_alloc), and use it wherever we consume peer_buf_alloc: - virtio_transport_get_credit() - virtio_transport_has_space() - virtio_transport_seqpacket_enqueue() 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 guest cannot force the host to queue more data than allowed by the host's 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 and the system only recovered after killing the QEMU process. With this patch applied, rerunning the same PoC yields: Before: MemFree: ~61.6 GiB MemAvailable: ~62.3 GiB Slab: ~142 MiB SUnreclaim: ~117 MiB After 32 high-credit connections: MemFree: ~61.5 GiB MemAvailable: ~62.3 GiB Slab: ~178 MiB SUnreclaim: ~152 MiB i.e. only ~35 MiB increase in Slab/SUnreclaim, no host OOM, and the guest remains responsive. Fixes: d021c344051a ("VSOCK: Introduce VM Sockets") Reported-by: Melbin K Mathew Signed-off-by: Melbin K Mathew --- net/vmw_vsock/virtio_transport_common.c | 27 ++++++++++++++++++++++--- 1 file changed, 24 insertions(+), 3 deletions(-) diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c index dcc8a1d58..f5afedf01 100644 --- a/net/vmw_vsock/virtio_transport_common.c +++ b/net/vmw_vsock/virtio_transport_common.c @@ -491,6 +491,25 @@ void virtio_transport_consume_skb_sent(struct sk_buff *skb, bool consume) } EXPORT_SYMBOL_GPL(virtio_transport_consume_skb_sent); +/* + * Return the effective peer buffer size for TX credit computation. + * + * The peer advertises its receive buffer via peer_buf_alloc, but we + * cap that to our local buf_alloc (derived from + * SO_VM_SOCKETS_BUFFER_SIZE and already clamped to buffer_max_size) + * so that a remote endpoint cannot force us to queue more data than + * our own configuration allows. + */ +static u32 virtio_transport_peer_buf_alloc(struct virtio_vsock_sock *vvs) +{ + u32 peer = vvs->peer_buf_alloc; + u32 local = vvs->buf_alloc; + + if (peer > local) + return local; + return peer; +} + u32 virtio_transport_get_credit(struct virtio_vsock_sock *vvs, u32 credit) { u32 ret; @@ -499,7 +518,8 @@ u32 virtio_transport_get_credit(struct virtio_vsock_sock *vvs, u32 credit) return 0; spin_lock_bh(&vvs->tx_lock); - ret = vvs->peer_buf_alloc - (vvs->tx_cnt - vvs->peer_fwd_cnt); + ret = virtio_transport_peer_buf_alloc(vvs) - + (vvs->tx_cnt - vvs->peer_fwd_cnt); if (ret > credit) ret = credit; vvs->tx_cnt += ret; @@ -831,7 +851,7 @@ virtio_transport_seqpacket_enqueue(struct vsock_sock *vsk, spin_lock_bh(&vvs->tx_lock); - if (len > vvs->peer_buf_alloc) { + if (len > virtio_transport_peer_buf_alloc(vvs)) { spin_unlock_bh(&vvs->tx_lock); return -EMSGSIZE; } @@ -882,7 +902,8 @@ static s64 virtio_transport_has_space(struct vsock_sock *vsk) struct virtio_vsock_sock *vvs = vsk->trans; s64 bytes; - bytes = (s64)vvs->peer_buf_alloc - (vvs->tx_cnt - vvs->peer_fwd_cnt); + bytes = (s64)virtio_transport_peer_buf_alloc(vvs) - + (vvs->tx_cnt - vvs->peer_fwd_cnt); if (bytes < 0) bytes = 0; -- 2.34.1