Re: [PATCH v2 1/3] Fix userfaultfd_api to return EINVAL as expected

[Andrew Morton]

On Sun, 23 Jun 2024 11:26:37 -0400 Peter Xu <peterx@xxxxxxxxxx> wrote:

> > > Fixes: e06f1e1dd499 ("userfaultfd: wp: enabled write protection in userfaultfd API")
> > 
> > A userspace-triggerable WARN is bad.  I added cc:stable to this.
> 
> Andrew,
> 
> Note that this change may fix a WARN, but it may also start to break
> userspace which might be worse if it happens, IMHO.  I forgot to mention
> that here, but only mentioned that in v1, and from that POV not copying
> stable seems the right thing.
> 
> https://lore.kernel.org/all/ZjuIEH8TW2tWcqXQ@x1n/
> 
>         In summary: I think we can stick with Fixes on e06f1e1dd499, but we
>         don't copy stable.  The major reason we don't copy stable here is
>         not only about complexity of such backport, but also that there can
>         be apps trying to pass in unsupported bits (even if the kernel
>         didn't support it) but keep using MISSING mode only, then we
>         shouldn't fail them easily after a stable upgrade.  Just smells
>         dangerous to backport.

OK.  And I'll move it into the 6.11-rc1 queue, for the next merge window.