Messages in this thread | | | Date | Tue, 7 Sep 2004 12:30:31 +0200 | From | Jens Axboe <> | Subject | Re: [PATCH] remember to check return value from __copy_to_user() in cdrom_read_cdda_old() |
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On Tue, Sep 07 2004, viro@parcelfarce.linux.theplanet.co.uk wrote: > On Tue, Sep 07, 2004 at 11:34:37AM +0200, Jens Axboe 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. > > access_ok() is far from being the only reason for error here. If area > is unmapped, we shouldn't silently lose data without any indication of > error.
it boils down to access_ok() not being sufficient on its own, and in which case yes we should just use copy_to_user() and kill the check completely as per the patch sent out.
-- Jens Axboe
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