netdev - Re: [RFC PATCH 4/6] hv_sock: Initialize send_buf in hvs_stream

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Date:   Fri, 15 Apr 2022 18:16:02 +0200
From:   Andrea Parri <parri.andrea@...il.com>
To:     "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
Cc:     KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
        Stefano Garzarella <sgarzare@...hat.com>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 4/6] hv_sock: Initialize send_buf in
 hvs_stream_enqueue()

> > > All fields are explicitly initialized, and in the data
> > > array, only the populated bytes are copied to the ring buffer.  There should not
> > > be any uninitialized values sent to the host.   Zeroing the memory ahead of
> > > time certainly provides an extra protection (particularly against padding bytes,
> > > but there can't be any since the layout of the data is part of the protocol with
> > > Hyper-V).
> > 
> > Rather than keeping checking that...
> 
> The extra protection might be obtained by just zero'ing the header (i.e., the
> bytes up to the 16 Kbyte data array).   I don't have a strong preference either
> way, so up to you.

A main reason behind this RFC is that I don't have either.  IIUC, you're
suggesting something like (the compiled only):


diff --git a/net/vmw_vsock/hyperv_transport.c b/net/vmw_vsock/hyperv_transport.c
index 092cadc2c866d..200f12c432863 100644
--- a/net/vmw_vsock/hyperv_transport.c
+++ b/net/vmw_vsock/hyperv_transport.c
@@ -234,7 +234,8 @@ static int __hvs_send_data(struct vmbus_channel *chan,
 {
 	hdr->pkt_type = 1;
 	hdr->data_size = to_write;
-	return vmbus_sendpacket(chan, hdr, sizeof(*hdr) + to_write,
+	return vmbus_sendpacket(chan, hdr,
+				offsetof(struct hvs_send_buf, data) + to_write,
 				0, VM_PKT_DATA_INBAND, 0);
 }
 
@@ -658,6 +659,7 @@ static ssize_t hvs_stream_enqueue(struct vsock_sock *vsk, struct msghdr *msg,
 	send_buf = kmalloc(sizeof(*send_buf), GFP_KERNEL);
 	if (!send_buf)
 		return -ENOMEM;
+	memset(send_buf, 0, offsetof(struct hvs_send_buf, data));
 
 	/* Reader(s) could be draining data from the channel as we write.
 	 * Maximize bandwidth, by iterating until the channel is found to be
-- 

Let me queue this for further testing/review...

Thanks,
  Andrea