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[87.16.204.83]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-488d5cf2e51sm185534185e9.1.2026.04.13.03.30.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 13 Apr 2026 03:30:54 -0700 (PDT) Date: Mon, 13 Apr 2026 12:30:50 +0200 From: Stefano Garzarella To: Dudu Lu Cc: netdev@vger.kernel.org, stefanha@redhat.com, mst@redhat.com, jasowang@redhat.com Subject: Re: [PATCH] vsock/virtio: fix accept queue count leak on transport mismatch in recv_listen Message-ID: References: <20260413085243.73200-1-phx0fer@gmail.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: <20260413085243.73200-1-phx0fer@gmail.com> On Mon, Apr 13, 2026 at 04:52:43PM +0800, Dudu Lu wrote: >virtio_transport_recv_listen() calls sk_acceptq_added(sk) to increment >the listener's accept queue counter before calling >vsock_assign_transport(). When vsock_assign_transport() fails or selects >a different transport than the one that received the packet, the error >path returns without calling sk_acceptq_removed(sk), permanently >incrementing sk_ack_backlog. > >A malicious VM peer can exploit this by sending repeated CONNECT >requests that trigger the transport mismatch condition. Each such >request permanently increments sk_ack_backlog. After approximately >backlog+1 such requests (default backlog ~128), sk_acceptq_is_full() >returns true, causing the listener to reject ALL new connections with >-ENOMEM. The only recovery is closing and re-creating the listener >socket. > >Compare with vmci_transport.c and hyperv_transport.c which correctly >place sk_acceptq_added() AFTER the transport check, avoiding this >issue entirely. > >Fix by moving sk_acceptq_added(sk) to after the transport validation >check, matching the pattern used by the other transports. The issue seems legitimate, but this patch doesn't do what you're describing here. Out of curiosity, how did you generate it? Stefano > >Fixes: c0cfa2d8a788 ("vsock: add multi-transports support") >Signed-off-by: Dudu Lu >--- > net/vmw_vsock/virtio_transport_common.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > >diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c >index 8a9fb23c6e85..29e1d9833be4 100644 >--- a/net/vmw_vsock/virtio_transport_common.c >+++ b/net/vmw_vsock/virtio_transport_common.c >@@ -1,3 +1,4 @@ >+ sk_acceptq_added(sk); > // SPDX-License-Identifier: GPL-2.0-only > /* > * common code for virtio vsock >@@ -1560,8 +1561,9 @@ virtio_transport_recv_listen(struct sock *sk, struct sk_buff *skb, > return -ENOMEM; > } > >- sk_acceptq_added(sk); > >+ >+ sk_acceptq_added(sk); > lock_sock_nested(child, SINGLE_DEPTH_NESTING); > > child->sk_state = TCP_ESTABLISHED; >-- >2.39.3 (Apple Git-145) >