On 06/25, Kees Cook wrote: > > On Wed, Jun 25, 2014 at 9:52 AM, Oleg Nesterov <oleg@xxxxxxxxxx> wrote: > > > > Yes, at least this should close the race with suid-exec. And there are no > > other users. Except apparmor, and I hope you will check it because I simply > > do not know what it does ;) > > > >> I wonder if changes to nnp need to "flushed" during syscall entry > >> instead of getting updated externally/asynchronously? That way it > >> won't be out of sync with the seccomp mode/filters. > >> > >> Perhaps secure computing needs to check some (maybe seccomp-only) > >> atomic flags and flip on the "real" nnp if found? > > > > Not sure I understand you, could you clarify? > > Instead of having TSYNC change the nnp bit, it can set a new flag, say: > > task->seccomp.flags |= SECCOMP_NEEDS_NNP; > > This would be set along with seccomp.mode, seccomp.filter, and > TIF_SECCOMP. Then, during the next secure_computing() call that thread > makes, it would check the flag: > > if (task->seccomp.flags & SECCOMP_NEEDS_NNP) > task->nnp = 1; > > This means that nnp couldn't change in the middle of a running syscall. Aha, so you were worried about the same thing. Not sure we need this, but at least I understand you and... > Hmmm. Perhaps this doesn't solve anything, though? Perhaps my proposal > above would actually make things worse, since now we'd have a thread > with seccomp set up, and no nnp. If it was in the middle of exec, > we're still causing a problem. Yes ;) > I think we'd also need a way to either delay the seccomp changes, or > to notice this condition during exec. Bleh. Hmm. confused again, > What actually happens with a multi-threaded process calls exec? I > assume all the other threads are destroyed? Yes. But this is the point-of-no-return, de_thread() is called after the execing thared has already passed (say) check_unsafe_exec(). However, do_execve() takes cred_guard_mutex at the start in prepare_bprm_creds() and drops it in install_exec_creds(), so it should solve the problem? Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
