Usenet 1994 January

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Text File | 1992-12-18 | 15.7 KB | 375 lines

Interested party please email wen-king@vlsi.cs.caltech.edu What is the purpose of FSP (V2.6): FSP is a set of programs that implements a public-access archive similar to an anonymous-FTP archive. It is not meant to be a replacement for ftp; it is only meant to do what anonymous-ftp does, but in a manner more acceptible to the provider of the service and more friendly to the clients. Providing anonymous-FTP service can be costly --- each active session consumes one process slot in the OS and one stream socket entry in the network sub-system. The servers can also run concurrently, adding to the system load. A popular archive site can easily be overwhelmed as a result. Some were forced to shutdown or and some impose inconvienent access restrictions. Unlike FTP, FSP is connection-less and virtually state-less. One server handles requests from all clients machines. Each active client machine takes up 16-bytes in a dynamically extensible table. Since only one server exists on a server machine at any time, the load added to the server machine is no more than one. In exchange for allowing site operators to keep their sites open and do away with cumbersome access restrictions, this is what the clients accept with FSP: 1) Lower transfer rate. The maximum rate is 1 kbyte per UDP message round-trip time between the client and the server. In addition to the potential for more abundant sites and more accessible sites, this is what the clients gain with FSP: 1) Robustness. Since FSP is connectionless, flucturations in the network will not abort a FSP transaction. Furthermore, the 16-bytes of data for each client can be regenerated at any point during any transaction. Thus, if the server goes down at any point during a transaction, the transaction will resume when the server is restarted. (like NFS) 2) Friendlier user interface. FSP does not have its own command interpretor like FTP. Since it is connectionless, there is no reason to carry much information from one command to the next, and the commands can all be made into individual unix programs. For instance, there is one program you run to list the directory and another you run to download a file. 3) Client protection. FSP oversees a directory structure similar to that of an anonymous-FTP. However, a directory created via FSP transaction is owned by the client machine that issued the creation request. The client can create and delete files and subdirectories in that directory. In addition, the client can enable any of the two attributes for that directory: A) Give all other clients the permission to create files and subdirectries. B) Give all other clients the permission to delete files and subdirectories. Note: A subdirectory can be deleted if it is empty and the client owns the subdirectory. 4) Server protection. FSP server does not spawn sub-programs. It will accept only paths that are downward relative to its designated working directory. On systems with symbolic links, the server will follow symbolic links, but it does not follow uplinks (".."). Clients cannot create symbolic links and care should be taken so that other users on the server machine cannot create symbolic links in the server's work space. It is also fairly difficult to formuate an attack to force a shutdown of a FSP site by actions of a rogue site. About the only way to distrupt a FSP service is to flood the FSP site with network packets. FSP server prevents itself from 'counter-flooding' by filtering for legitimate requests using the following method: A) Each request message contains a key. For each client, server database contains the keys to be used for the next client request and for the previous client request. B) If the next request does not contain a key that matches either of the two keys, it is accepted only if at least one minute has elapsed since the last time a request is accepted. If the key does match the old key (retransmit by client) it is accepted if the elapse time is greater than 3 seconds. C) Every request message accepted is acknowledged with one reply message. The reply message contains a new key to used for the next request. The new key is computed by the server with a pseudo-random number generator. Flooding is a ballant violation of network etiquette because a site can be subjected to flooding attack whether it has FSP running or not, and flooding congests every link and gateway between the rogue client and the server. As a further measure of protection, the server loads a table of rogue clients on startup. The server will not respond to requests from any of those clients. The software set: common_def.h This C header file contains definitions common to both the server code and the client code. client_def.h This C header file contains definitions for the client code. server_def.h This C header file contains definitions for the server code. udp_io.c This file contains the lowest level routines that deal with the unix inet sockets. This file is used by both the server code and the client code. server_main.c Main routine and dispatch loop for the server. server_host.c Routines for maintaining client database. server_file.c Routines for file i/o. server_lib.c Routines for inet socket i/o. client_lib.c Core routines of the client library. client_util.c Supplementry routines of the client library. client_lock.c udp packet multiplexing mechanism. bsd_src/ Directory containing additional sources derived from those in public archive on uunet.uu.net. It contains a BSD random/srandom routine, a modified BSD globbing routine, a modified "ls" source. fcdcmd.c These compiles into individual client utilities. fgetcmd.c Those with a "cmd" in their name will do their flscmd.c own globbing on their argv base on directory fprocmd.c information obtained from the server. frmcmd.c frmdircmd.c fcatcmd.c fmkdir.c fput.c fver.c fgrab.c merge.c This file is used to call the other client programs when program merging option is used. Rather than compiling into individual client utility programs, users may opt to build a single program which contains all client funtionalities, which are to be distinguished at run time by the name used to activate the program. Significant space saving can be achieved on some machines. Compilation: FSP has been compiled and tested by me on a SS-2 running SunOs 4.1.1, a HP-9000 running HP UNIX, a VAX-780 running 4.3-tahoe, and a 386 box running system-V UNIX with old Excelan ethernet interface. It has also been compiled on a variety of machines by over hundreds users all over the world. To compile the software, you must first successfully complete a "make" in the bsd_src directory. You may have to change a few files. In particular, you may have to edit "Makefile" and "tweak.h" in bsd_src directory. When that is done, you can edit the Makefile on the top directory and run "make" in the top directory, or "make merge" if you want to combine all client programs into one single file. You may wish to read through the rest of this document first before making changes to the Makefile. After "make" or "make merge" finished, you may use "make install" or "make install-merge" to install the programs. Man pages may be installed by "make installm". IMPORTANT NOTE: You do not need to run the fspd process if you only want to access existing fsp archives. fspd processs is needed only if you want to setup and archive for public access. Server Administration: The only things you need for setting up a FSP server is a work directory for the service and and the FSP server itself (fspd). fspd can run independently or it can be run under inetd. When running independently, fspd waits for messages through a UDP socket whoes port number is defined in the Makefile. When running under inetd, fspd is involked as in.fspd. inetd will spawn fspd when a message arrives for the FSP socket. The fspd process will take over and stick around to wait on additional messages. After it has become idle for 2 minutes, fspd will exit and return control to inetd. Sample setup for inetd operation: In /etc/services file: fsp 21/udp fspd In /etc/inetd.conf file: fsp dgram udp wait ftp /usr/etc/fspd in.fspd In this sample, the same port number for ftp is used for the fsp socket. There will not be a conflict because ftp uses stream protocol, and fsp uses UDP protocol. The fspd program in this example is ran under user 'ftp'. In addition, fspd will accept these flags: -h absolute_path Set fsp work directory. Overrides the compiled-in default. -p udp_port_number Set UDP port number. Overrides the compiled-in default. -u uid_number Assume this uid after startup. If present, fspd will attempt a setuid() to this uid number. It will exit if setuid() fails. -d Turn on debug mode. The stdio files will remain open in debugging mode. When fspd starts, it chdir to its work directory where it looks for (and reads in if found) a list of internet numbers in the standard 4-part form: ddd.ddd.ddd.ddd in the file ".ROGUE_HOSTS". This file is prepared by the FSP maintainer, and is used to indicate that fspd should not respond to any requests from these machines. After that, it begins to service any requests it gets on the UDP socket. If a file .OWN.XXXXXXXX, where XXXXXXXX is an 8-digit hex number, exists in a directory in fspd's work space, the directory is owned by the machine whoes inet number is XXXXXXXX (an integer stored in the network byte order), where the number is printed as a hexadecimal number. If no such file exists, the directory has no owner. (Note, the 'dot' files are hidden from clients). If the file .FSP_OK_DEL does not exists in a directory, only the owner is allowed to remove items from that directory. If the file .FSP_OK_ADD does not exists in a directory, only the owner is allowed to add items into that directory. Thus, you typically want to protect the top directory by leaving out the .FSP_OK_DEL, .FSP_OK_ADD files, and .OWN.XXXXXXXX files in the top directory. Clients do not get to read the directory information directly. Instead, fspd maintains a directory listing for each directory in a cache file. If the directory is writable by fspd, or if a writable file in it is prepared beforehand, fspd will store the directory information in .FSP_CONTENT file in that directory. Otherwise, it will store the information in a pair of files (with hashed names) in a special directory specified by the variable DEF_DIRECTORY_CACHE in Makefile. The later allows read-only directories to be exported. When a client requests information for a directory, the cache file is created if it doesn't exist, and it is rebuilt if it is out of date. The information is accessed by having the client read the directory listing file. Care is taken so that the client will not get corrupted entries when the directory is changed while the listing is being read. Files being uploaded are first written to a temporary file in the work directory: .TXXXXXXXXYYYY where XXXXXXXX is the inet number of the client, and YYYY is the port number of the client program. When upload is compelete, the file is moved into the intended location. Sending it an 'alarm' signal will cause fspd to dump its current client database into the file .HTAB_DUMP in the work directory. This can be useful for debugging and for catching rogue clients. Client utilities: All inter-command states are kept in these three shell environment variables. FSP_PORT Port number of the fspd you wish to contact. FSP_HOST Host name or number of the fspd. FSP_DIR Your current working directory in the archive. When multiple client utilities are run at the same time on the same client machine, packet multiplexing mechanisms can be used to enable concurrent access to the same fsp database. If none of the mechanisms are selected at compile time, FSP_LOCALPORT can be used to ensure that only once client utility can run at any time. In this case, FSP_LOCALPORT can be set to any port number not current used on the client machine. FSP_TRACE can be set if you want status reports be printed while files are being transferred. FSP_DELAY variable can be used to set the retransmit interval for client utilities (in thousandth of a second). The retransmit rate is adjusted in an exponential manner, until the retry rate reaches 5 mintes per retry. FSP_BUF_SIZE can be set to a positive number less than or equal to 1024. When set, it determines the size of data to be send for each request during file and directory information transfer. The default is 1024. Some sites are connected via links that cannot transmit buffers containing 1024 bytes of data in addition to the header information. Setting FSP_BUF_SIZE to a lower value will allow these sites to access fsp archives. A typical setup looks like this: setenv FSP_PORT 21 setenv FSP_HOST 131.215.131.97 setenv FSP_DIR / setenv FSP_TRACE setenv FSP_DELAY 3000 setenv FSP_BUF_SIZE 1024 (All examples will be in csh. However, it is assumed that similar things can be done with other shells) For commands that do globbing using remote directory info, normal shell globbing needs to be turned off. In csh, it can be done with a set of aliases: alias fcd setenv FSP_DIR \`$set noglob\; exec fcdcmd \!\*$\` alias fls $set noglob\; exec flscmd \!\*$ alias fget $set noglob\; exec fgetcmd \!\*$ alias fgrab $set noglob\; exec fgrabcmd \!\*$ alias fcat $set noglob\; exec fcatcmd \!\*$ alias frm $set noglob\; exec frmcmd \!\*$ alias frmdir $set noglob\; exec frmdircmd \!\*$ alias fpro $set noglob\; exec fprocmd \!\*$ In addtion, these alias are useful: alias fpwd echo \$FSP_DIR on \$FSP_HOST port \$FSP_PORT alias fsethost setenv FSP_DIR \/\; setenv FSP_HOST \!\:1\; \ setenv FSP_PORT \!\:2 The second one is a user contribution. It allows one to set the FSP_HOST, FSP_PORT, and to initialize FSP_DIR in one command. Commands: fver display server's version number. fcd change current remote directory, like cd. fls list directory. works like ls. fget get the named files. fgrab get the named file and delete it from remote directory. fput put the named files. fcat get the named files and send them to stdout. fmkdir make named directories. frm delete named files. frmdir delete named directories. fpro no arg: display directory protection modes. +c: give others permission to create new items. -c: deny others permission to create new items. +d: give others permission to delete old items. -d: deny others permission to delete old items. *********************************************************************** This is a free software. Be creative; make your own macros and tools and let me know of any bugs and suggestions. A mailing list for the discussion of the FSP software is now available (started Oct 2, 1992.) To get on the list, send an email stating that you want to be on the FSP list to the following address: listmaster@Germany.EU.net Articles to be distributed to the subscribers should be sent to the following email address: fsp-discussion@Germany.EU.net