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    SubjectRe: UTF-8 practically vs. theoretically in the VFS API (was: Re: JFS default behavior)
    Linus Torvalds wrote:
    > Which flies in the face of "Be strict in what you generate, be liberal in
    > what you accept". A lot of the functions are _not_ willing to be liberal
    > in what they accept. Which sometimes just makes the problem worse, for no
    > good reason.

    Unicode specifies that a program claiming to read UTF-8 _must_ reject
    malformed UTF-8.

    Ok, we can just ignore Unicode. :)

    But the reason they cite is security: when applications allow
    malformed UTF-8 through, there's plenty of scope for security holes
    due to multiple encodings of "/" and "." and "\0".

    This is a real problem: plenty of those Windows worms that attack web
    servers get in by using multiple-escaped funny characters and
    malformed UTF-8 to get past security checks for ".." and such.

    In theory these are not problems; all programs should be liberal in
    what they accept, and robust in handling data from the outside world.

    In practice, programs quickly lose track of which text is from the
    outside world and which is from a trusted source or checked source.
    These worms are quite successful at exploiting things the programmers
    didn't think of. Being _conservative_ at all places which scan UTF-8
    does seem like it might help a little.

    -- Jamie
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