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idea: chroot :: FilePath -> IO a -> IO a
by David Roundy 21 Apr '03

21 Apr '03

I have the idea that we ought to be able to implement the equivalent of a unix chroot command, but all within the haskell IO monad. So the idea would be that if I want to do some operation that only requires access to, say /var/cache/test, but involves user-provided input which I don't trust (and if I don't want to trust the security of my parsing of the possibly malicious input), I could run: chroot "/var/cache/test" $ complicated_function "/" scary_user_input which would be the equivalent of complicated_function "/var/cache/test" scary_user_input except that every file and directory access (read or write or stat or whatever) would be forced to be in a subdirectory of /var/cache/test. Moreover, calls such as system would not be allowed (that is, they'd throw an isChrootError exception), since such calls of course could not be verified to touch no file outside of /var/cache/test (at least not using only haskell). Actually, there are two ways this could be done. One is the one mentioned above, which is roughly equivalent to a unix chroot. Another (now that I think about it, probably more elegant) would be to implement a restrict_access type of function, which wouldn't change the meaning of any file paths as a chroot does, but would simply cause any access outside of the specified directory to fail. This would have the advantage of being transparent to the writer of complicated_function--and might be extended to allow access to more than one directory (e.g. for a webserver of only static pages maybe /var/www and /etc/myserver/). As I see it, implementing such a function would require support in the IO monad (some of which may already be there?), since it would need to know for each primitive operation which arguments are file paths, plus whether that operation is even legal in a chroot environment. Or perhaps it's the other way around, and every primitive operation would need to support chroot... I know I would find such a function exceedingly comforting, since I wonder from time to time what would happen if users stick weird filenames in the wrong places, or make symlinks to things they should not have access to. And the cool thing is that with haskell's monadic IO, I think it could be done in a very elegant manner, and in such a way that it is natural (and simple) to wrap a chroot around individual operations, giving finer grained control than I can imagine doing any other way. Any ideas whether such a feat would be possible, and if so how hard it would be? -- David Roundy http://www.abridgegame.org

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Re: HI
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18 Apr '03

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Re: Parsec question
by Sarat Chandra 17 Apr '03

17 Apr '03

Thanks, "uust" was the missing link. --- Doaitse Swierstra <doaitse(a)cs.uu.nl> wrote: >It is in: > >http://cvs.cs.uu.nl/cgi-bin/cvsweb.cgi/uust/lib/ > >As far as I can see you should be able to check the whole uust tree out, > > Doaitse > > >On donderdag, apr 17, 2003, at 17:06 Europe/Amsterdam, Sarat Chandra >wrote: > >> Doaitse, >> >> I can't find the "Parsing" directory. May be the directory is not >> made visible to public. However, under the "PC" directory, I see >> UU_Parsing.hs and other files (but no examples directory). Can you >> please check it. >> >> Thanks. >> >> --- Doaitse Swierstra <doaitse(a)cs.uu.nl> wrote: >>> Parsec cannot do this. If you want this behaviour check out the >>> Parsing >>> library at cvs.cs.uu.nl (directory lib). In the examples directory you >>> find an example parser for Haskell written using these combinators. At >>> the top level there is also a Tiger compiler that is written with >>> these >>> combinators, >>> >>> Doaitse Swierstra >>> >>> >>> On woensdag, apr 16, 2003, at 12:00 Europe/Amsterdam, Sarat Chandra >>> wrote: >>> >>>> I am using Parsec to write a parser. I would like to know >>>> how parse-errors can be accumulated without stopping at the >>>> first error. I would like to skip the input upto some >>>> synchronization point (for e.g a semi-colon) and continue parsing >>>> from there. Thanks. >>>> >>>> _____________________________________________________________ >>>> Get your own FREE e-mail account at http://www.volcanomail.com >>>> >>>> _____________________________________________________________ >>>> Select your own custom email address for FREE! Get you(a)yourchoice.com >>>> w/No Ads, 6MB, POP & more! >>>> http://www.everyone.net/selectmail?campaign=tag >>>> _______________________________________________ >>>> Haskell-Cafe mailing list >>>> Haskell-Cafe(a)haskell.org >>>> http://www.haskell.org/mailman/listinfo/haskell-cafe >> >> _____________________________________________________________ >> Get your own FREE e-mail account at http://www.volcanomail.com >> >> _____________________________________________________________ >> Select your own custom email address for FREE! Get you(a)yourchoice.com >> w/No Ads, 6MB, POP & more! >> http://www.everyone.net/selectmail?campaign=tag >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe _____________________________________________________________ Get your own FREE e-mail account at http://www.volcanomail.com _____________________________________________________________ Select your own custom email address for FREE! Get you(a)yourchoice.com w/No Ads, 6MB, POP & more! http://www.everyone.net/selectmail?campaign=tag

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Re: Parsec question
by Sarat Chandra 17 Apr '03

17 Apr '03

Doaitse, I can't find the "Parsing" directory. May be the directory is not made visible to public. However, under the "PC" directory, I see UU_Parsing.hs and other files (but no examples directory). Can you please check it. Thanks. --- Doaitse Swierstra <doaitse(a)cs.uu.nl> wrote: >Parsec cannot do this. If you want this behaviour check out the Parsing >library at cvs.cs.uu.nl (directory lib). In the examples directory you >find an example parser for Haskell written using these combinators. At >the top level there is also a Tiger compiler that is written with these >combinators, > > Doaitse Swierstra > > >On woensdag, apr 16, 2003, at 12:00 Europe/Amsterdam, Sarat Chandra >wrote: > >> I am using Parsec to write a parser. I would like to know >> how parse-errors can be accumulated without stopping at the >> first error. I would like to skip the input upto some >> synchronization point (for e.g a semi-colon) and continue parsing >> from there. Thanks. >> >> _____________________________________________________________ >> Get your own FREE e-mail account at http://www.volcanomail.com >> >> _____________________________________________________________ >> Select your own custom email address for FREE! Get you(a)yourchoice.com >> w/No Ads, 6MB, POP & more! >> http://www.everyone.net/selectmail?campaign=tag >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe _____________________________________________________________ Get your own FREE e-mail account at http://www.volcanomail.com _____________________________________________________________ Select your own custom email address for FREE! Get you(a)yourchoice.com w/No Ads, 6MB, POP & more! http://www.everyone.net/selectmail?campaign=tag

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Parsec question
by Sarat Chandra 16 Apr '03

16 Apr '03

I am using Parsec to write a parser. I would like to know how parse-errors can be accumulated without stopping at the first error. I would like to skip the input upto some synchronization point (for e.g a semi-colon) and continue parsing from there. Thanks. _____________________________________________________________ Get your own FREE e-mail account at http://www.volcanomail.com _____________________________________________________________ Select your own custom email address for FREE! Get you(a)yourchoice.com w/No Ads, 6MB, POP & more! http://www.everyone.net/selectmail?campaign=tag

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Say�n haskell-cafe ,Baskuda.Com`da Bebek / Oyuncak Kategorisi A��ld�!
by Baskuda-4233 16 Apr '03

16 Apr '03

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RE: [OT[ proving programs for novices
by David Bakin 16 Apr '03

16 Apr '03

How would this book relate - in subject, difficulty, audience - to: The Science of Programming by Gries? Algebra of Programming by Bird, De Moor, Moor? Thanks! - Dave -----Original Message----- From: Doaitse Swierstra [mailto:doaitse@cs.uu.nl] Sent: Tuesday, April 15, 2003 12:38 PM To: Bill Wood Cc: Doaitse Swierstra; haskell-cafe(a)haskell.org Subject: Re: [OT[ proving programs for novices One might be interested in the newly published book by Roland Backhouse: "Program Construction : Calculating Implementations from Specifications" http://www.wiley.com/remtitle.cgi?0470848820 I quote from the publishers web site: "The ever-increasing dependence of our lives and livelihoods on the correct functioning of computer software means that logic and program correctness are core elements of all good computer science degrees. This book presents both these topics in one self-contained text. The focus of the book is on "correct-by-construction" program design -- the discipline of calculating programs from their specifications. Modern, calculational logic is introduced in combination with key program construction principles, such as the assignment axiom, loop invariants and bound functions. This material is intertwined with motivational discussion, programming examples and challenging problem-solving exercises, bringing the book alive for its intended audience, undergraduates in computer science and mathematics, as well as professional programmers wishing to further develop their programming skills. The book covers the elements of logic and program correctness that form the foundations of further study --- the logical connectives and their algebraic properties, induction, quantifiers and program construction rules. Substantial examples of program construction are included. Many exercises are provided, all with detailed solutions. " Doaitse Swierstra _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

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[OT[ proving programs for novices
by Chris Moline 15 Apr '03

15 Apr '03

hi. this isnt a haskell question but i am hoping you will forgive it. i was wondering where i could find books/websites/tutorials on how to construct proofs and how to prove programs. preferably books that are aimed at novices with some programming experience but little math/logic experience. i have paul hudaks hsoe book which has some material on proving properties of programs. sincerely chris moline

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wiki problems
by Isaac Jones 14 Apr '03

14 Apr '03

Greetings, Not sure who to send this to: I noticed on the wiki that the HaskellNewbies page was blank for some reason, and when I attempted to put something there, I got the below error. I tried this over the course of two days just to make sure there wasn't actually an editing conflict. "Editing Conflict Another author has modified this page since you checked it out. So that you won't interfere with the other author's work, you need to reload, re-edit, and submit again. Sorry!" peace, isaac

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linesPS is not analagous to lines
by David Roundy 14 Apr '03

14 Apr '03

I've just switched my code to use PackedStrings rather than Strings for file contents, and ran into what appears to be a bug in the Data.PackedString module in ghc 5.04.3. unlines is the inverse of lines, since lines converts empty lines into empty strings. linesPS, however, ignores empty lines. :( It seems like it would be a good idea to either fix this (which might not be a good idea, if existing code depends on its current behavior), or add a note in the documentation that it isn't analagous to lines, so that other people won't make the same mistake based on its similar name. My example program that demonstrates this: import Data.PackedString main = do temp <- return $ packString "hello\nworld\n\nI\njust\nskipped\n\n a line\n" putStr $ "The unlines of linesPSed version:\n\n" putStr $ unlines $ map unpackPS $ linesPS temp putStr $ "The unlines of linesed version:\n\n" putStr $ unlines $ lines $ unpackPS temp -- David Roundy http://www.abridgegame.org

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