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From:   "Andrea Parri (Microsoft)" <parri.andrea@gmail.com>
To:     KY Srinivasan <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Wei Liu <wei.liu@kernel.org>, Dexuan Cui <decui@microsoft.com>,
        Michael Kelley <mikelley@microsoft.com>,
        Stefano Garzarella <sgarzare@redhat.com>,
        David Miller <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>
Cc:     linux-hyperv@vger.kernel.org,
        virtualization@lists.linux-foundation.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        "Andrea Parri (Microsoft)" <parri.andrea@gmail.com>
Subject: [RFC PATCH 3/6] hv_sock: Add validation for untrusted Hyper-V values
Date:   Wed, 13 Apr 2022 22:47:39 +0200
Message-Id: <20220413204742.5539-4-parri.andrea@gmail.com>
In-Reply-To: <20220413204742.5539-1-parri.andrea@gmail.com>
References: <20220413204742.5539-1-parri.andrea@gmail.com>
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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@gmail.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)
 		return -EIO;
 
 	if (payload_len == 0)
-- 
2.25.1