hwrng: virtio - Fix race on data_avail and actual data

In the Linux kernel, the following vulnerability has been resolved: hwrng: virtio - Fix race on data_avail and actual data The virtio rng device kicks off a new entropy request whenever the data available reaches zero. When a new request occurs at the end of a read operation, that is, when the result of that request is only needed by the next reader, then there is a race between the writing of the new data and the next reader. This is because there is no synchronisation whatsoever between the writer and the reader. Fix this by writing data_avail with smp_store_release and reading it with smp_load_acquire when we first enter read. The subsequent reads are safe because they're either protected by the first load acquire, or by the completion mechanism. Also remove the redundant zeroing of data_idx in random_recv_done (data_idx must already be zero at this point) and data_avail in request_entropy (ditto).

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Linux kernel 安全漏洞

Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于data_avail和实际数据之间存在竞争条件，可能导致读取过时数据。

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