--- David Howells <dhowells@xxxxxxxxxx> wrote: > Casey Schaufler <casey@xxxxxxxxxxxxxxxx> wrote: > > > The specification of your push interface that the push operation > > not affect how others access the process is OK for SELinux, but > > not for any other MAC scheme that I've dealt with, and I think > > that's most of them. Nuts. Smack, for example, uses exactly one > > label on the process for all purposes. > > It's a fairly important concept. The victimisation security context on a > process must not change, even if the kernel overrides the security context > that that process acts as so that it can transparently do work on its behalf. > > IMO, the right way to do this is to pass the security context directly to > vfs_mkdir() and co. > > > Are you concerned about accesses other than signals? Signals > > could be staitforward to deal with in a pushed situation, but > > I'd hesitate to say that the solution would generalize without > > additional thought. > > There's also /proc and ptrace() for example. ps -z must not show the > overridden state. > > > > > > (5) int security_xfrm_to_kernel_context(void *from, void **_to); > > > > > > > > Woof. What are you transforming from? > > > > > > In CacheFiles case, the cachefilesd daemon's security label into the > label > > > the cache driver acts as on behalf of other processes. > > > > I'm not sure I understand what this is doing. > > CacheFiles consists of two parts: the kernel module which creates things in > the cache and does accesses into the cache on behalf of processes that access > cached filesystems, and the userspace daemon that builds cull tables and > deletes things. > > The reason there are two security labels is that the daemon's label gives it > just enough rights to be able to do its job. More or less all it can do is > lookup, opendir, readdir, stat, rmdir, unlink and open the chardev for > talking > to the kernel module. This means that the daemon can't, for example, be made > to read or modify cache storage objects. > > Thus means, however, that the daemon's label isn't sufficient for the kernel > module to do its job. But since there's no way for the kernel module to > directly get a label (and indeed it doesn't know the label it needs), a > transformation has to be applied that turns the process label used by the > daemon into a process label that the kernel, and only the kernel, can use. > > The kernel's label gives it, amongst other things, the additional rights to > do > mkdir, creat, open, read, write, setxattr, getxattr, rename - things the > daemon isn't allowed to do. With Smack you can leave the label alone, raise CAP_MAC_OVERRIDE, do your business of setting the label correctly, and then drop the capability. No new hooks required. Casey Schaufler casey@xxxxxxxxxxxxxxxx - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
