On 4/17/19 4:39 PM, Paul Moore wrote: > On Wed, Apr 17, 2019 at 12:27 PM Oleg Nesterov <oleg@xxxxxxxxxx> wrote: >> On 04/17, Paul Moore wrote: >>> >>> On Wed, Apr 17, 2019 at 10:57 AM Oleg Nesterov <oleg@xxxxxxxxxx> wrote: >>>> On 04/17, Paul Moore wrote: >>>>> >>>>> I'm tempted to simply return an error in selinux_setprocattr() if >>>>> the task's credentials are not the same as its real_cred; >>>> >>>> What about other modules? I have no idea what smack_setprocattr() is, >>>> but it too does prepare_creds/commit creds. >>>> >>>> it seems that the simplest workaround should simply add the additional >>>> cred == real_cred into proc_pid_attr_write(). >>> >>> Yes, that is simple, but I worry about what other LSMs might want to >>> do. While I believe failing if the effective creds are not the same >>> as the real_creds is okay for SELinux (possibly Smack too), I worry >>> about what other LSMs may want to do. After all, >>> proc_pid_attr_write() doesn't change the the creds itself, that is >>> something the specific LSMs do. >> >> Yes, but if proc_pid_attr_write() is called with cred != real_cred then >> something is already wrong? > > True, or at least I would think so. > > Looking at the current tree there are three LSMs which implement > setprocattr hooks: SELinux, Smack, and AppArmor. I know Casey has > already mentioned that he wasn't able to trigger the problem in Smack, > but looking at smack_setprocattr() I see the similar commit_creds() > usage so I would expect the same problem in Smack; what say you Casey? > Looking at apparmor_setprocattr(), it appears that it too could end > up calling commit_creds() via aa_set_current_hat(). > > Since it looks like all three LSMs which implement the setprocattr > hook are vulnerable I'm open to the idea that proc_pid_attr_write() is > a better choice for the cred != read_cred check, but I would want to > make sure John and Casey are okay with that. > > John? heh yeah, seems I messed up our check, we actually have if (current_cred() != current_real_cred()) return -EBUSY; on the change_profile path and missed it on the change_hat one. It makes sense to lift the check up earlier
