On Tue, Nov 24, 2020 at 06:15:36PM +0100, Greg KH wrote: > On Tue, Nov 24, 2020 at 06:06:38PM +0100, Jann Horn wrote: > > +seccomp maintainers/reviewers > > [thread context is at > > https://lore.kernel.org/linux-api/87lfer2c0b.fsf@xxxxxxxxxxxxxxxxxxxxxxxxx/ > > ] > > > > On Tue, Nov 24, 2020 at 5:49 PM Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > > > On Tue, Nov 24, 2020 at 03:08:05PM +0100, Mark Wielaard wrote: > > > > For valgrind the issue is statx which we try to use before falling back > > > > to stat64, fstatat or stat (depending on architecture, not all define > > > > all of these). The problem with these fallbacks is that under some > > > > containers (libseccomp versions) they might return EPERM instead of > > > > ENOSYS. This causes really obscure errors that are really hard to > > > > diagnose. > > > > > > So find a way to detect these completely broken container run times > > > and refuse to run under them at all. After all they've decided to > > > deliberately break the syscall ABI. (and yes, we gave the the rope > > > to do that with seccomp :(). > > > > FWIW, if the consensus is that seccomp filters that return -EPERM by > > default are categorically wrong, I think it should be fairly easy to > > add a check to the seccomp core that detects whether the installed > > filter returns EPERM for some fixed unused syscall number and, if so, > > prints a warning to dmesg or something along those lines... > > Why? seccomp is saying "this syscall is not permitted", so -EPERM seems > like the correct error to provide here. It's not -ENOSYS as the syscall > is present. > > As everyone knows, there are other ways to have -EPERM be returned from > a syscall if you don't have the correct permissions to do something. > Why is seccomp being singled out here? It's doing the correct thing. The correct solution to this problem is simple: the standard and the problematic container runtimes need to be fixed to return ENOSYS as I said in my first mail. Imho, the kernel neither should need to log anything or be opinionated about what error is correct or not. Imho, this is a broken standard and that's where the story ends. We've had that argument about ENOSYS being the correct errno in such scenarios in userspace already and that's been ignored for _years_. Now, as could be expected it's suddenly the kernel who's supposed to fix this. That's totally wrong imho. Christian
