Messages in this thread |  | | | Date | Tue, 7 Sep 2004 13:42:31 +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 12:30:31PM +0200, Jens Axboe wrote: > > 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. > > access_ok() is just "we can trust MMU to do the right thing when dealing > with access to process address space at that address". On platforms with > secondary address spaces (e.g. sparc) it's always true. On something like > i386 we *could* use segments for the same purposes. In fact, we used to > do just that - access to userland memory went with %fs as segment (thus > the names like extinct memcpy_fromfs() and surviving set_fs()). However, > it's cheaper to do that check explicitly instead of relying on MMU. And > that's what access_ok() does.
Alright, I'm wondering how the misconception of what access_ok() really guarantees snuck into cdrom.c. At least the patch takes care of it.
-- Jens Axboe
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