59 lines
2.5 KiB
Text
59 lines
2.5 KiB
Text
extensions/filter module documentation
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--------------------------------------
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The filter extension implements message content filtering using
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solanum's hook framework and Intel's Hyperscan regular expression
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matching library.
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It requires an x86_64 processor with SSSE3 extensions.
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To operate, the filter requires a database of regular expessions
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that have been compiled using the Hyperscan library's
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hs_compile_multi() or hs_compile_ext_multi() functions.
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The command SETFILTER is used to manage operation of the filter and to
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load compiled Hyperscan databases.
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General documenation of SETFILTER is available using the 'HELP SETFILTER'
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command.
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For each expression in the database, the three least significant bits
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of the expression ID are used to indicate which action the ircd should
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take in the event of a match:
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001 (1) DROP - The message will be dropped and the client will be sent
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an ERR_CANNOTSENDTOCHAN message.
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010 (2) KILL - The connection from which the message was recevied will
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be closed.
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100 (4) ALARM - A Server Notice will be generated indicating that an
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expression was matched. The nick, user, hostname and
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IP address will be reported. For privacy, the expression
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that has been matched will not be disclosed.
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Messages are passed to the filter module in a format similar to an
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IRC messages:
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0:nick!user@host#1 PRIVMSG #help :hello!
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The number at the start of the line indicates the scanning pass:
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Messages are scanned twice, once as they were received (0), and once
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with any formatting or unprintable characters stripped (1).
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By default, 'nick', 'user' and 'host' will contain *. This behaviour
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can be changed at build time if filtering on these fields is required.
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The number after the # will be 0 or 1 depending on whether the sending
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client was identified to a NickServ account.
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The process for loading filters is as follows:
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1. The Hyperscan database is serialized using hs_serialize_database().
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2. A 'SETFILTER NEW' command is sent.
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3. The serialized data is split into chunks and base64 encoded.
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The chunk size needs to be chosen to ensure that the resuliting
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strings are short enough to fit into a 510 byte IRC line, taking
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into account space needed for the 'SETFILTER +' command, check field,
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server mask, and base64 overhead.
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4. The encoded chunks are sent using 'SETFILTER +' commands
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5. Once the entire database has been sent, a 'SETFILTER APPLY' command
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is sent to commit it.
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