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17 Mar 17 07:13
Mauro Leggieri
Join Date: 02 Jun 2016
Posts To This List: 37
FilterGetMessage and insufficient buffers

Hi, Because couldn't find documentation nor samples, I did some reverse engineering on FilterGetMessage/FltSendMessage/etc. calls and would like to confirm the behavior if the buffer that receives a message or reply from/to driver is not large enough. Based on what I see, assuming we are sending a message from driver to usermode 1) If buffer size of FilterGetMessage is small, the API will return ERROR_INSUFFICIENT_BUFFER or ERROR_MORE_DATA and we can retry the call using a larger buffer. FltSendMessage will wait for a new request from usermode. 2) When we call FilterReplyMessage with a larger buffer FltSendMessage expects to receive, FltSendMessage will return STATUS_BUFFER_OVERFLOW or STATUS_BUFFER_TOO_SMALL. Usermode will get the win32 error. Sounds right? Regards, Mauro.
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