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    SubjectRe: [PATCH 2/2] Version 9 (2.6.24-rc1) Smack: Simplified Mandatory Access Control Kernel
    On Sat, Oct 27, 2007 at 11:01:12AM +0200, Ahmed S. Darwish wrote:
    > The problem here (As discussed in private mails) is that the for loop
    > assumes that the beginning of given user-space buffer is the beginning
    > of a rule. This leads to situations where the rule becomes "ecret 20",
    > or "cret 20" instead of "Secret 20". Big input buffers/files leads
    > smack to recieve a rule like "Secret 20" in fragmented chunks like:
    > write("<lots of rules before ours>\nSec", ..)
    > write("r", 1, ..)
    > write("et 20\n<remaing rules after ours>", ..)
    > Parsing a rule in such tough conditions in _kernel space_ is very
    > hard. I began to feel that it will be much easier if we do the parsing
    > in a userspace utility and let smack accept only small buffers (80 char).

    For crying out louf, all it takes is a finite state machine... BTW, folks,
    your parser *and* input language suck. Really. Silently allowing noise
    is Dumb(tm).

    Please, write the grammar down and _follow_ _it_. AFAICS, trimming the
    crap ("we have a number, skip everything until '/', whatever noise we
    have there doesn't matter") leads to something like

    text: (whitespace line? \n)*
    whitespace: [ \t]*
    line: label whitespace number whitespace (/ whitespace set whitespace)?
    set: number (whitespace , whitespace number)*
    label: [!-.0-~]{1,23}
    number: [0-9]+

    and even that might be too liberal. For fsck sake, all you need is to
    keep a struct that would contain
    * state
    * (partial) number
    * list of smack_known, with the first element being the partial one.
    * number of characters already seen in label (label itself stored
    in the list head ->smk_known)
    and that's it - just have a switch by ->state to handle the next character.
    Allocate that struct in ->open(), modify in ->write(), apply the entire thing
    at once in ->release().

    Come on, people, this is ridiculous - why bother reinventing the wheels for
    the stuff that belongs to exercises halfway through any self-respecting
    introductory textbook? Scary parser, my arse...
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      Last update: 2007-10-28 01:49    [W:0.021 / U:0.216 seconds]
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