On Sun, Jan 15, 2012 at 12:16 PM, Casey Schaufler <casey@xxxxxxxxxxxxxxxx> wrote: > On 1/14/2012 12:22 PM, Linus Torvalds wrote: >> >> And yes, I really seriously do believe that is both safer and simpler >> than some model that says "you can drop stuff", and then you have to >> start making up rules for what "dropping" means. >> >> Does "dropping" mean allowing setuid(geteuid()) for example? That *is* >> dropping the uid in a _POSIX_SAVED_IDS environment. And I'm saying >> that no, we should not even allow that. It's simply all too "subtle". > > > I am casting my two cents worth behind Linus. Dropping > privilege can be every bit as dangerous as granting privilege > in the real world of atrocious user land code. Especially in > the case of security policy enforcing user land code. Can you think of *any* plausible attack that is possible with my patch (i.e. no_new_privs allows setuid, setresuid, and capset) that would be prevented or even mitigated if I blocked those syscalls? I can't. (The sendmail-style attack is impossible with no_new_privs.) Also, how would you even block setuid(2) in a non-confusing manner? The semantics and error returns are already such a disaster than it's barely worth it for anything to check the return value. > > This even more important in environments that support fine > granularity of privilege, including capabilities and SELinux. > Under SELinux a domain transition can increase, decrease or > completely change a process' access rights and there is really > no way for the kernel to tell which it is because that's all > encoded in the arbitrary SELinux policy. Smack does not try > to maintain a notion of hierarchy of privilege, so the notion > of any change being equivalent to any other is in line with > the Smack philosophy. > My patch does not (barring bugs) allow selinux domain transitions. I certainly think that all security transitions that vary across distributions should be blocked by no_new_privs. --Andy -- 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
