linux-kernel - Re: [PATCH] mm/mprotect: Fix do_mprotect

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Date:   Thu, 6 Apr 2023 18:04:37 -0400
From:   "Liam R. Howlett" <Liam.Howlett@...cle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-next@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] mm/mprotect: Fix do_mprotect_pkey() return on error

* Andrew Morton <akpm@...ux-foundation.org> [230406 17:53]:
> On Thu,  6 Apr 2023 15:30:50 -0400 "Liam R. Howlett" <Liam.Howlett@...cle.com> wrote:
> 
> > When the loop over the VMA is terminated early due to an error, the
> > return code could be overwritten with ENOMEM.  Fix the return code by
> > only setting the error on early loop termination when the error is not
> > set.
> > 
> > Fixes: 2286a6914c77 ("mm: change mprotect_fixup to vma iterator")
> > Cc: <stable@...r.kernel.org>
> 
> I do think we should always describe the user-visible effects when
> proposing a backport.
> 
> a) so the -stable maintainers understand why we're recommending the
>    backport and
> 
> b) to help some poor soul who is looking at the patch wondering if
>    it will fix his customer's bug report.

Thanks, I'll keep this in mind.

> 
> How's this?
> 
> : User-visible effects include: attempts to run mprotect() against a special
> : mapping or with a poorly-aligned hugetlb address should return -EINVAL,
> : but they presently return -ENOMEM.

That sounds reasonable, although this isn't an exhaustive list. It could
be an -EACCESS for multiple reasons, or anything the vm_ops returns.