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

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Date: Mon, 24 Jun 2024 15:57:34 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Peter Xu <peterx@...hat.com>
Cc: Audra Mitchell <audra@...hat.com>, viro@...iv.linux.org.uk,
 brauner@...nel.org, jack@...e.cz, aarcange@...hat.com,
 rppt@...ux.vnet.ibm.com, shli@...com, linux-fsdevel@...r.kernel.org,
 linux-kernel@...r.kernel.org, shuah@...nel.org,
 linux-kselftest@...r.kernel.org, raquini@...hat.com
Subject: Re: [PATCH v2 1/3] Fix userfaultfd_api to return EINVAL as expected

On Sun, 23 Jun 2024 11:26:37 -0400 Peter Xu <peterx@...hat.com> 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.