Re: [PATCH] clone: only use lower 32 flag bits

[Christian Brauner]

On Wed, May 06, 2020 at 12:06:10PM -0700, Joe Perches wrote:
> On Tue, 2020-05-05 at 19:44 +0200, Christian Brauner wrote:
> > Jan reported an issue where an interaction between sign-extending clone's
> > flag argument on ppc64le and the new CLONE_INTO_CGROUP feature causes
> > clone() to consistently fail with EBADF.
> []
> > Let's fix this by always capping the upper 32 bits for the legacy clone()
> > syscall. This ensures that we can't reach clone3() only features by
> > accident via legacy clone as with the sign extension case and also that
> > legacy clone() works exactly like before, i.e. ignoring any unknown flags.
> > This solution risks no regressions and is also pretty clean.
> > 
> > I've chosen u32 and not unsigned int to visually indicate that we're
> > capping this to 32 bits.
> 
> Perhaps use the lower_32_bits macro?

Oh neat, I wasn't aware of this helper since there are no users under
kernel/*

Christian