copying-files.md: fixed 2 typos

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Steve Phillips 2017-04-19 02:06:54 -07:00 committed by GitHub
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On inter-qube file copy security
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The scheme is *secure* because it doesn't allow other qubes to steal the files that are being copying, and also doesn't allow the source qube to overwrite arbitrary file on the destination qube. Also, Qubes file copy scheme doesn't use any sort of virtual block devices for file copy -- instead we use Xen shared memory, which eliminates lots of processing of untrusted data. For example, the receiving qube is *not* forced to parse untrusted partitions or file systems. In this respect our file copy mechanism provides even more security than file copy between two physically separated (air-gapped) machines!
The scheme is *secure* because it doesn't allow other qubes to steal the files that are being copying, and also doesn't allow the source qube to overwrite arbitrary files on the destination qube. Also, Qubes's file copy scheme doesn't use any sort of virtual block devices for file copy -- instead we use Xen shared memory, which eliminates lots of processing of untrusted data. For example, the receiving qube is *not* forced to parse untrusted partitions or file systems. In this respect our file copy mechanism provides even more security than file copy between two physically separated (air-gapped) machines!
However, one should keep in mind that performing a data transfer from *less trusted* to *more trusted* qubes can always be potentially insecure, because the data that we insert might potentially try to exploit some hypothetical bug in the destination qube (e.g. a seemingly innocent JPEG that we copy from an untrusted qube might contain a specially crafted exploit for a bug in JPEG parsing application in the destination qube). This is a general problem and applies to any data transfer between *less trusted to more trusted* qubes. It even applies to the scenario of copying files between air-gapped machines. So, you should always copy data only from *more trusted* to *less trusted* qubes.