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    SubjectRe: [PATCH] remember to check return value from __copy_to_user() in cdrom_read_cdda_old()
    Jens Axboe <axboe@suse.de> wrote:
    >
    > On Tue, Sep 07 2004, Andrew Morton wrote:
    > > Jens Axboe <axboe@suse.de> wrote:
    > > >
    > > > On Tue, Sep 07 2004, Paul Mackerras wrote:
    > > > > Jens Axboe writes:
    > > > >
    > > > > > __copy_to_user is the unchecking version of copy_to_user.
    > > > >
    > > > > It doesn't range-check the address, but it does return non-zero
    > > > > (number of bytes not copied) if it encounters a fault writing to the
    > > > > user buffer.
    > > >
    > > > but it doesn't matter, if it returns non-zero then something happened
    > > > between the access_ok() and the actual copy because the user app did
    > > > something silly. so I don't care much really, I think the major point is
    > > > the kernel will cope.
    > > >
    > > > you could remove the access_ok() and change it to a copy_to_user()
    > > > instead, I don't care either way. it's the old and slow interface which
    > > > really never is used unless things have gone wrong anyways.
    > > >
    > >
    > > Sure, but at present if an application tries to read cdrom data to address
    > > 0x00000000 (say), the kernel will return "success". It should return an
    > > error code. (Actually, it should return a short read if any data was
    > > transferred, but whatever).
    >
    > Because access_ok() isn't reliable?

    access_ok() simply checks that the address is in the 0x00000000 -
    0xbfffffff range. We can still get faults in that range.


    > There is another bug in there though, ret is never returned if
    > cdrom_read_block() fails.

    yup.
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