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Order of operations error and missing exception handling #22

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ChopperCharles opened this issue Jul 24, 2019 · 0 comments

ChopperCharles commented Jul 24, 2019

In NDisDriver.c, line 1531 the following code will always evaluate to 0:

tag_us = (qinfo.TagHeader.UserPriority & 0x07 << 13) |
(qinfo.TagHeader.CanonicalFormatId & 0x01 << 12) |
(qinfo.TagHeader.VlanId & 0x0FFF);

This is because the shift operations take precedence over the and operations. To correct this, add parenthesis as such:

tag_us = ((qinfo.TagHeader.UserPriority & 0x07) << 13) |
((qinfo.TagHeader.CanonicalFormatId & 0x01) << 12) |
(qinfo.TagHeader.VlanId & 0x0FFF);

In addition, anywhere there is a ProbeForRead or ProbeForWrite, these should be surrounded by a _try / _except block (and so should any additional access to the buffers). See https://docs.microsoft.com/en-us/windows-hardware/drivers/ddi/content/wdm/nf-wdm-probeforread for more information.

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