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Thu, 30 Apr 2026 06:04:41 -0700 (PDT) Received: from leonardi-redhat ([176.206.19.176]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48a82301b7bsm71336415e9.11.2026.04.30.06.04.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 30 Apr 2026 06:04:40 -0700 (PDT) Date: Thu, 30 Apr 2026 15:04:37 +0200 From: Luigi Leonardi To: Yiqi Sun Cc: kvm@vger.kernel.org, virtualization@lists.linux.dev, 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 Subject: Re: [PATCH] vsock/virtio: fix vsockmon info leak in non-linear tap copy Message-ID: References: <20260430071110.380509-1-sunyiqixm@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: <20260430071110.380509-1-sunyiqixm@gmail.com> On Thu, Apr 30, 2026 at 03:11:10PM +0800, Yiqi Sun wrote: >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 > Thanks for the fix! Tested using vsock_loopback sending zero-copy packets. Payload is always zero before the fix. Reviewed-by: Luigi Leonardi