Crash in dissect_smb2_command

[Paul Offord <Paul.Offord () advance7 com>]

Hi,

Between 2.2 and the latest git a change seems to have been made to dissect_smb2_getinfo_request().  It now returns an 
integer based on the difference between two dissected values:

               offset = getinfo_offset + getinfo_size;

               return offset;

Unfortunately getinfo_offset and getinfo_size are sometimes zero and so a zero offset is returned.  On return to 
dissect_smb2_command there's some fiddling around until we get to:

               proto_item_set_len(cmd_item, offset-old_offset);

The calculation of offset-old_offset yields a negative number which is passed to proto_item_set_len as a length 
parameter.  In proto_item_set_len we have:

               DISSECTOR_ASSERT(length >= 0);

Obviously this causes an exception.

Do I just feed this back as commentary on the Patch Set or should I raise a bug?  If the former, can you point me to 
the change because I can't seem to find it?

Thanks and regards...Paul


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