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SubjectRe: [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@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)

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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