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 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)) so a huge flag causes an array index out of bounds and either explodes here or continues onto SELinux where it BUG(). So this is regression. It would have gotten an EPERM, now it gets a BUG/panic. Yes ATI needs to fix their driver, but we broke it and I don't remember the driver not working on 2.6.24 and earlier.... -Eric -- This message was distributed to subscribers of the selinux mailing list. If you no longer wish to subscribe, send mail to majordomo@xxxxxxxxxxxxx with the words "unsubscribe selinux" without quotes as the message.
