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    SubjectRe: [PATCH 0/3][RFC] ioctl dispatcher
    Arjan van de Ven wrote:
    >> While ioctls are officially ugly, they are the best choice for some
    >> use cases, not to mention compatibility issues. Currently ioctl
    >> writers face the following hurdles:
    >> - if the ioctl uses a data buffer, the ioctl handler must allocate
    >> kernel memory for this buffer
    >> - the memory may be allocated on the heap or on the stack,
    >> depending on the buffer size
    >> - handle any errors from the operation
    >> - copy the data from userspace, if necessary
    >> - handle any errors from the operation
    >> - actually perform the operation
    >> - copy the data back to userspace, if necessary
    >> - handle any errors from the operation
    >> - free the buffer, if allocated from the heap
    >> The first patch automates these operations, only requiring the caller
    >> to supply the ioctl number and a callback in a table.
    > this doesn't seem to be much different from the way the DRM code deals
    > with ioctls. Or the V4L code.
    > Personally I hate that code though.....
    > There is a fine balance here; between driver writers screwing something
    > up they shouldn't be doing in the first place and us being able to
    > clearly see what the code is doing; your patch kinda hides some key
    > elements of the ioctl path...

    Which key elements?

    It hides the big switch (ioctl), memory allocation, and error handling,
    and exposes the actual ioctl-specific code, which I thought was the key

    Why are we interested in boilerplate?

    > I'm afraid it gives a false sense of
    > security though. Not having to deal with one aspect of security just to
    > have to deal with the rest....

    It reduces the number of potential mistakes a driver author can make.

    > Lets put it this way: if the driver author has to type "copy_from_user"
    > there's a chance that he'll remember that the data comes from the user
    > and isn't to be trusted on face value.

    I'll rename the argp variable to argp_user_supplied.

    I can't believe you think writing the copy code from scratch (or worse,
    copy/paste) each time helps security.

    I have a truly marvellous patch that fixes the bug which this
    signature is too narrow to contain.

     \ /
      Last update: 2008-09-27 19:53    [W:0.021 / U:67.568 seconds]
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