> On Tue, 2008-09-30 at 10:38 -0500, Serge E. Hallyn wrote:
> > 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)
>
> Well, you save a branch and won't get the pagefault so it does 'fix' the
> pagefault/panic from cap code. It doesn't tell us when others screw up
> and SELinux is still possibly going to BUG(). We are also going to
> actually be returning a permission decision not on what was requested
> but on something wholely different.
