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Thu, 30 Apr 2026 00:11:56 -0700 (PDT) Received: from localhost.localdomain ([189.1.242.96]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-834ed7ecf57sm4049605b3a.50.2026.04.30.00.11.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 30 Apr 2026 00:11:55 -0700 (PDT) From: Yiqi Sun To: kvm@vger.kernel.org, virtualization@lists.linux.dev Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, stefanha@redhat.com, sgarzare@redhat.com, mst@redhat.com, jasowang@redhat.com, xuanzhuo@linux.alibaba.com, eperezma@redhat.com, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, Yiqi Sun Subject: [PATCH] vsock/virtio: fix vsockmon info leak in non-linear tap copy Date: Thu, 30 Apr 2026 15:11:10 +0800 Message-Id: <20260430071110.380509-1-sunyiqixm@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 vsockmon mirrors packets through virtio_transport_build_skb(), which builds a new skb and copies the payload into it. For non-linear skbs, this goes through virtio_transport_copy_nonlinear_skb(). Helper manually initializes a iov_iter, but leaves iov_iter.count unset. As a result, skb_copy_datagram_iter() sees zero writable bytes in the destination iterator and copies no payload data. This becomes an info leak because virtio_transport_build_skb() has already reserved payload_len bytes in the new skb with skb_put(). The skb is then returned to the tap path with that payload area still uninitialized, so userspace reading from a vsockmon device can observe heap contents and potentially kernel address. Fix it by initializing iov_iter.count to the number of bytes to copy. Fixes: 4b0bf10eb077 ("vsock/virtio: non-linear skb handling for tap") Signed-off-by: Yiqi Sun --- net/vmw_vsock/virtio_transport_common.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c index 416d533f493d..6b26ee57ccab 100644 --- a/net/vmw_vsock/virtio_transport_common.c +++ b/net/vmw_vsock/virtio_transport_common.c @@ -152,7 +152,7 @@ static void virtio_transport_copy_nonlinear_skb(const struct sk_buff *skb, iov_iter.nr_segs = 1; to_copy = min_t(size_t, len, skb->len); - + iov_iter.count = to_copy; skb_copy_datagram_iter(skb, VIRTIO_VSOCK_SKB_CB(skb)->offset, &iov_iter, to_copy); } -- 2.34.1