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Date:   Thu, 21 Apr 2022 16:08:05 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     "Andrea Parri (Microsoft)" <parri.andrea@...il.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>,
        Michael Kelley <mikelley@...rosoft.com>,
        David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, linux-hyperv@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/5] hv_sock: Add validation for untrusted Hyper-V values

On Wed, Apr 20, 2022 at 10:07:18PM +0200, Andrea Parri (Microsoft) wrote:
>For additional robustness in the face of Hyper-V errors or malicious
>behavior, validate all values that originate from packets that Hyper-V
>has sent to the guest in the host-to-guest ring buffer.  Ensure that
>invalid values cannot cause data being copied out of the bounds of the
>source buffer in hvs_stream_dequeue().
>
>Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@...il.com>
>---
> include/linux/hyperv.h           |  5 +++++
> net/vmw_vsock/hyperv_transport.c | 11 +++++++++--
> 2 files changed, 14 insertions(+), 2 deletions(-)
>
>diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
>index fe2e0179ed51e..55478a6810b60 100644
>--- a/include/linux/hyperv.h
>+++ b/include/linux/hyperv.h
>@@ -1663,6 +1663,11 @@ static inline u32 hv_pkt_datalen(const struct vmpacket_descriptor *desc)
> 	return (desc->len8 << 3) - (desc->offset8 << 3);
> }
>
>+/* Get packet length associated with descriptor */
>+static inline u32 hv_pkt_len(const struct vmpacket_descriptor *desc)
>+{
>+	return desc->len8 << 3;
>+}
>
> struct vmpacket_descriptor *
> hv_pkt_iter_first_raw(struct vmbus_channel *channel);
>diff --git a/net/vmw_vsock/hyperv_transport.c b/net/vmw_vsock/hyperv_transport.c
>index 8c37d07017fc4..092cadc2c866d 100644
>--- a/net/vmw_vsock/hyperv_transport.c
>+++ b/net/vmw_vsock/hyperv_transport.c
>@@ -577,12 +577,19 @@ static bool hvs_dgram_allow(u32 cid, u32 port)
> static int hvs_update_recv_data(struct hvsock *hvs)
> {
> 	struct hvs_recv_buf *recv_buf;
>-	u32 payload_len;
>+	u32 pkt_len, payload_len;
>+
>+	pkt_len = hv_pkt_len(hvs->recv_desc);
>+
>+	/* Ensure the packet is big enough to read its header */
>+	if (pkt_len < HVS_HEADER_LEN)
>+		return -EIO;
>
> 	recv_buf = (struct hvs_recv_buf *)(hvs->recv_desc + 1);
> 	payload_len = recv_buf->hdr.data_size;
>
>-	if (payload_len > HVS_MTU_SIZE)
>+	/* Ensure the packet is big enough to read its payload */
>+	if (payload_len > pkt_len - HVS_HEADER_LEN || payload_len > HVS_MTU_SIZE)

checkpatch warns that we exceed 80 characters, I do not have a strong 
opinion on this, but if you have to resend better break the condition 
into 2 lines.

Maybe even update or remove the comment? (it only describes the first 
condition, but the conditions are pretty clear, so I don't think it adds 
much).

Thanks,
Stefano

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