> Quoting Eric Paris (
eparis@redhat.com):
> > On Wed, 2008-10-01 at 00:23 +1000, James Morris wrote:
> > > On Tue, 30 Sep 2008, Eric Paris wrote:
> > >
> > > > This patch adds a WARN_ONCE() to cap_capable() so we will stop
> > > > dereferencing random spots of memory and will cleanly tell the obviously
> > > > broken driver that it doesn't have that ridiculous permissions. No idea
> > > > if the driver is going to handle EPERM but anything that calls capable
> > > > and doesn't expect a denial has got to be the worst piece of code ever
> > > > written..... I could return EINVAL, but I think its clear that noone
> > > > has capabilities over 64 so clearly they don't have that permission.
> > > >
> > > > This 'could' be considered a regression since 2.6.24. Neither SELinux
> > > > nor the capabilities system had a problem with ginormous request values
> > > > until we got 64 bit support, although this is OBVIOUSLY a bug with the
> > > > out of tree closed source driver....
> > >
> > > An issue here is whether we should be adding workarounds in the mainline
> > > kernel for buggy closed drivers. Papering over problems rather than
> > > getting them fixed does not seem like a winning approach. Especially
> > > problems which are unexpectedly messing with kernel security APIs.
> >
> > I don't know, looking at the feelings on "Can userspace bugs be kernel
> > regressions" leads me to believe that when we break something that once
> > worked we are supposed to fix it.
> >
> >
http://lwn.net/Articles/292143/
> >
> > I don't think the proprietary closed source nature of the driver makes
> > it any less our problem
>
> The kernel-space nature of the driver is the distinction here.
>
> > to not make changes which cause the kernel to
> > esplode.
> >
> > > Also, won't this encourage vendors of such drivers to continue with this
> > > behavior, while discouraging those vendors who are doing the right thing?
> >
> > Discouraging people who open source their drivers and put them in the
> > kernel? obviously not. encouraging crap? well, I hope we fix
> > regressions no matter how they are found...
> >
> > > Do we know if this even really helps the user? For all we know, the
> > > driver may simply crash differently with an -EPERM.
> >
> > Well, before the 64 bit capabilities change we did:
> >
> > (cap_t(c) & CAP_TO_MASK(flag))
> >
> > so a huge value for "flag" got masked off.
> >
> > After 64 bit capabilities we do:
> >
> > ((c).cap[CAP_TO_INDEX(flag)] & CAP_TO_MASK(flag))
>
> Perhaps we should have CAP_TO_INDEX mask itself?
>
> #define CAP_TO_INDEX(x) (((x) >> 5) & _KERNEL_CAPABILITY_U32S)
