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    Subject[PATCH 3/6] Drivers: hv: vmbus: Avoid double fetch of payload_size in vmbus_on_msg_dpc()
    Date
    vmbus_on_msg_dpc() double fetches from payload_size.  The double fetch
    can lead to a buffer overflow when (mem)copying the hv_message object.
    Avoid the double fetch by saving the value of payload_size into a local
    variable.

    Reported-by: Juan Vazquez <juvazq@microsoft.com>
    Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
    ---
    drivers/hv/vmbus_drv.c | 17 +++++++----------
    1 file changed, 7 insertions(+), 10 deletions(-)

    diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
    index 82b23baa446d7..0e39f1d6182e9 100644
    --- a/drivers/hv/vmbus_drv.c
    +++ b/drivers/hv/vmbus_drv.c
    @@ -1056,6 +1056,7 @@ void vmbus_on_msg_dpc(unsigned long data)
    void *page_addr = hv_cpu->synic_message_page;
    struct hv_message *msg = (struct hv_message *)page_addr +
    VMBUS_MESSAGE_SINT;
    + __u8 payload_size = msg->header.payload_size;
    struct vmbus_channel_message_header *hdr;
    enum vmbus_channel_message_type msgtype;
    const struct vmbus_channel_message_table_entry *entry;
    @@ -1089,9 +1090,8 @@ void vmbus_on_msg_dpc(unsigned long data)
    goto msg_handled;
    }

    - if (msg->header.payload_size > HV_MESSAGE_PAYLOAD_BYTE_COUNT) {
    - WARN_ONCE(1, "payload size is too large (%d)\n",
    - msg->header.payload_size);
    + if (payload_size > HV_MESSAGE_PAYLOAD_BYTE_COUNT) {
    + WARN_ONCE(1, "payload size is too large (%d)\n", payload_size);
    goto msg_handled;
    }

    @@ -1100,21 +1100,18 @@ void vmbus_on_msg_dpc(unsigned long data)
    if (!entry->message_handler)
    goto msg_handled;

    - if (msg->header.payload_size < entry->min_payload_len) {
    - WARN_ONCE(1, "message too short: msgtype=%d len=%d\n",
    - msgtype, msg->header.payload_size);
    + if (payload_size < entry->min_payload_len) {
    + WARN_ONCE(1, "message too short: msgtype=%d len=%d\n", msgtype, payload_size);
    goto msg_handled;
    }

    if (entry->handler_type == VMHT_BLOCKING) {
    - ctx = kmalloc(sizeof(*ctx) + msg->header.payload_size,
    - GFP_ATOMIC);
    + ctx = kmalloc(sizeof(*ctx) + payload_size, GFP_ATOMIC);
    if (ctx == NULL)
    return;

    INIT_WORK(&ctx->work, vmbus_onmessage_work);
    - memcpy(&ctx->msg, msg, sizeof(msg->header) +
    - msg->header.payload_size);
    + memcpy(&ctx->msg, msg, sizeof(msg->header) + payload_size);

    /*
    * The host can generate a rescind message while we
    --
    2.25.1
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      Last update: 2020-11-18 15:39    [W:4.033 / U:0.064 seconds]
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