From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 A28DA30BF52 for ; Fri, 8 May 2026 15:50:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778255454; cv=none; b=lTWP49M58nYl8/zAizOqUfSl8tZQazW8OK3uKSVpbNRCVU3HxNqDHAAKUty4bICvcaZTvbFYAW3XVYCtG43xLIOjKrc+kbYy1PEaWkVyrarb7WW9BdBYVQptzBcrrucEihD6NJ5j2vWRUQElvg/hyjIW1NdsmOdrxbA7OlVFoJI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778255454; c=relaxed/simple; bh=rdDtrTgIi+rN4hhDCNeEhPYuXlZ/J2y+H8n1qLpmtsY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: In-Reply-To:Content-Type:Content-Disposition; b=Hra58uS5g7jTT3ivUMwl6szdQkyt0Lu2U/JpavvpBO+hUHo2hZoU51x1LLwTfwlecpNp47/NCsUPr2SqlbzBLh+bovoHKwXnh2NE660V+lS6UxNOo7hqT0g6F7BA4C5LU3wUYKKSbtKwVGwCIicArMwI4ocBvjt1/oqotSdsP24= 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=aoG6h6uw; arc=none smtp.client-ip=170.10.133.124 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="aoG6h6uw" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1778255449; 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=ZdBAwN+ZE1eYNiJtu0H0OHxl4J/6xgxxgGUcknEIPjk=; b=aoG6h6uwWfwPj4Oa7tfZ84TXZPd6AtyEmI8NiLKu8gKOShX/BqNkcKajnizu4aU/VigkYo O24rQeO9AtgTGt6t2ZzJzbDkAPxxz8O+adKaswWd9quzmy99cz7cF9Xcr2BkZerIRHS18X aSTCZygcYaIzd6WHVJn8MblQGo7ps6w= Received: from mail-wm1-f69.google.com (mail-wm1-f69.google.com [209.85.128.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-564-bLCKTegpPRGAszXN-Gtlng-1; Fri, 08 May 2026 11:50:48 -0400 X-MC-Unique: bLCKTegpPRGAszXN-Gtlng-1 X-Mimecast-MFC-AGG-ID: bLCKTegpPRGAszXN-Gtlng_1778255447 Received: by mail-wm1-f69.google.com with SMTP id 5b1f17b1804b1-4891f97aef0so11469845e9.2 for ; Fri, 08 May 2026 08:50:48 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1778255447; x=1778860247; 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=ZdBAwN+ZE1eYNiJtu0H0OHxl4J/6xgxxgGUcknEIPjk=; b=BvCDeYQ4f4PKzAmRrFXz/h6GfBFufrscyes1OICaI8+yWmlziwRRw93syWUQakl+Rt nxQhY22E7ZgxliUtPO5CncdD1+A9a9GSfmt3/b2LY/ce7/DiYbBB+pgDDTAWDijgAhEf pKIsNtQqXp+n68BXGd2dkgu0FbEg5LD3pLycVoAhyfo0eIfrSC0YcO77nJItfnhAvlcf 4rHwYRidCbGIz7bUF+8as2cLav7WZ3KVfre3UhlGcOY1dyJ2WFKvWjAO1gXyo6DTZqVd Bxu23dTBOC9FulE6FOuP1hZ58synAtcVeE24hq88aAFwPb1CgJcAdmHFgrXyScFs+hUw R8Lg== X-Forwarded-Encrypted: i=1; AFNElJ+grlTVEqDleEswrg8WFxWwPVqjgw+pY3YID1vXFcIvijgUJlZtP3Q3mGTf+9awGQi/EgiFtjVYssSE+rHTgg==@lists.linux.dev X-Gm-Message-State: AOJu0YyJhaYN1zPDDLH6P+mf/k/q2fdO8S1LQYRZ5/ItrZQJxx/ohBzD w2XllgyxsDVqzmWWj6c2y/jnTra7glhTspRy3b5zHm0uEbPiefyj3P4znMv0bKmE9w+PVUVI6F/ wDu7L+PDALq1z7OXqbG4nZxasoKU8Ut7LVWag2D/M+1Xpqnh7vSU8OzPcOQPkkQuyh2qG X-Gm-Gg: AeBDiety76vGGsQw/nNxl+/s0PwuC0j/q13FIJUenga0T3/2IBLUpvQN88ptMgTElWn ry2/q/69OwAUKoOySi+Dxmpe7b2VPQr79qU4pQIeyeGjsl+sLd+L2EmJRXD79VZlfFJgeeYZSrD xIK6Cmvx4azrvOEK90/218GPTQTpBVlmVA8c4h1wgfh/1gaDPfbh2VELKy2HNeRWILso7LOMWAB LMxWkEK0kvEKzlxfsjxwmpJA3zwaBCXXSQHVgQu6XYypDL0v/lgLD28Y4A+Y6+OUtatTYvOiWXR PM06hUDakqQTIx1/k2wdbIun/laBEn4G0cOJW5QNXHFhclZxyjJhgklGSjKfZD+JPWUHUzhXteL e8jnD+l2JXG+g1MLcq0bd7E8ujW4DJ8oXpn5QLrpuLbBeEMpEChjKZb3RSYYqJmI= X-Received: by 2002:a05:600c:8485:b0:48a:58ae:9933 with SMTP id 5b1f17b1804b1-48e51f32806mr210416085e9.18.1778255446899; Fri, 08 May 2026 08:50:46 -0700 (PDT) X-Received: by 2002:a05:600c:8485:b0:48a:58ae:9933 with SMTP id 5b1f17b1804b1-48e51f32806mr210415475e9.18.1778255446303; Fri, 08 May 2026 08:50:46 -0700 (PDT) Received: from sgarzare-redhat (host-87-11-6-2.retail.telecomitalia.it. [87.11.6.2]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48e6db11fc4sm2280025e9.27.2026.05.08.08.50.44 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 08 May 2026 08:50:45 -0700 (PDT) Date: Fri, 8 May 2026 17:50:24 +0200 From: Stefano Garzarella To: Arseniy Krasnov Cc: Paolo Abeni , Bobby Eshleman , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, "Michael S. Tsirkin" , Jason Wang , Xuan Zhuo , Yiqi Sun , kvm@vger.kernel.org, virtualization@lists.linux.dev Subject: Re: [PATCH] vsock/virtio: fix vsockmon info leak in non-linear tap, copy Message-ID: References: Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: cAOCCmgYNqc0BZoui99fzShqsC7BBhSuZtOrBI3RkTw_1778255447 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline On Thu, May 07, 2026 at 11:03:57PM +0300, Arseniy Krasnov wrote: >>CCing Arseniy and Bobby. > >Thanks! > >> >>On Tue, May 05, 2026 at 12:26:21PM +0200, Paolo Abeni wrote: >>>On 4/30/26 9:11 AM, 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); >>> >>>@Stefano, @Stefan, the patch LGTM, but sashiko pointed out to a >>>pre-existing issue you should probably want to address: >>> >>>> to_copy = min_t(size_t, len, skb->len); >>>Does this length calculation account for the offset when a packet is >>>split across multiple transmissions? >>>If a packet is requeued, VIRTIO_VSOCK_SKB_CB(skb)->offset is increased, >>>but to_copy still evaluates to the full length of the skb. >> >>Yep, I just checked and vhost-vsock is the only place where we call >>virtio_transport_deliver_tap_pkt() wiht an offset != 0, but I agree that >>we should also fix it. > >Yes, looks like the only place where offset could be non zero is 'vhost_transport_do_send_pkt()'. >And we set valid length in header every attempt to send it: > > /* Set the correct length in the header */ > hdr->len = cpu_to_le32(payload_len); > >In all other places we call 'virtio_transport_deliver_tap_pkt()' with offset == 0. And thus >skb->len == hdr->len. > >So for me looks ok. E.g. len in header is actual data. > >> >>Looking better in net/vmw_vsock/virtio_transport_common.c I think this >>is a regression, indeed we have this comment in >>virtio_transport_build_skb(): >> >> /* A packet could be split to fit the RX buffer, so we can retrieve >> * the payload length from the header and the buffer pointer taking >> * care of the offset in the original packet. >> */ >> pkt_hdr = virtio_vsock_hdr(pkt); >> >>Before commit 71dc9ec9ac7d ("virtio/vsock: replace virtio_vsock_pkt with >>sk_buff") we read the payload lenght from the header that is always set >>to the right value before delivering the packet to the tap. >> >> From that commit, we don't to consider the offset anymore since we >>started to use `len` from the skb, so IMO we should go back to what we >>did before it, I mean: >> >> payload_len = le32_to_cpu(pkt->hdr.len); >> >>@Bobby do you remember why we did that change? Or if you see any issue >>going back to what we did initially? >> >> >>Also IMO we should avoid to set all the iov_iter fields by hand and >>start to use iov_iter_kvec(). Plus, we can just use >>skb_copy_datagram_iter() in any case, like we already do in vhost-vsock, >>since it already handles linear vs non linear. >> >>At the end I mean something like this: >> >>@@ -171,7 +150,7 @@ static struct sk_buff *virtio_transport_build_skb(void *opaque) >> * care of the offset in the original packet. >> */ >> pkt_hdr = virtio_vsock_hdr(pkt); >>- payload_len = pkt->len; >>+ payload_len = le32_to_cpu(pkt_hdr->len); >> >> skb = alloc_skb(sizeof(*hdr) + sizeof(*pkt_hdr) + payload_len, >> GFP_ATOMIC); >>@@ -214,13 +193,17 @@ static struct sk_buff *virtio_transport_build_skb(void *opaque) >> skb_put_data(skb, pkt_hdr, sizeof(*pkt_hdr)); >> >> if (payload_len) { >>- if (skb_is_nonlinear(pkt)) { >>- void *data = skb_put(skb, payload_len); >>+ struct iov_iter iov_iter; >>+ struct kvec kvec; >>+ void *data = skb_put(skb, payload_len); >> >>- virtio_transport_copy_nonlinear_skb(pkt, data, payload_len); >>- } else { >>- skb_put_data(skb, pkt->data, payload_len); >>- } >>+ kvec.iov_base = data; >>+ kvec.iov_len = payload_len; >>+ iov_iter_kvec(&iov_iter, READ, &kvec, 1, payload_len); >>+ >>+ skb_copy_datagram_iter(pkt, >>+ VIRTIO_VSOCK_SKB_CB(pkt)->offset, >>+ &iov_iter, payload_len); >> } >> >> return skb; >> >>And removing virtio_transport_copy_nonlinear_skb(). > >Yes, this looks shorter and better. Thanks for confirming, I'll send a series soon and CC you. Please review it :-) Thanks, Stefano