linux-kernel - Re: [PATCH] mm/mincore: allow for making sys

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Message-ID: <CAHk-=wgy+1YT-Rhj5qWb_aCuBADhcq42GDKHB74sqrnOVPKzPg@mail.gmail.com>
Date:   Thu, 24 Jan 2019 09:35:32 +1300
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Jiri Kosina <jikos@...nel.org>
Cc:     Dominique Martinet <asmadeus@...ewreck.org>,
        Andy Lutomirski <luto@...capital.net>,
        Josh Snyder <joshs@...flix.com>,
        Dave Chinner <david@...morbit.com>,
        Matthew Wilcox <willy@...radead.org>,
        Jann Horn <jannh@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Michal Hocko <mhocko@...e.com>, Linux-MM <linux-mm@...ck.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: [PATCH] mm/mincore: allow for making sys_mincore() privileged

On Thu, Jan 24, 2019 at 9:27 AM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> I've reverted the 'let's try to just remove the code' part in my tree.
> But I didn't apply the two other patches yet. Any final comments
> before that should happen?

Side note: the inode_permission() addition to can_do_mincore() in that
patch 0002, seems to be questionable. We do

+static inline bool can_do_mincore(struct vm_area_struct *vma)
+{
+       return vma_is_anonymous(vma)
+               || (vma->vm_file && (vma->vm_file->f_mode & FMODE_WRITE))
+               || inode_permission(file_inode(vma->vm_file), MAY_WRITE) == 0;
+}

note how it tests whether vma->vm_file is NULL for the FMODE_WRITE
test, but not for the inode_permission() test.

So either we test unnecessarily in the second line, or we don't
properly test it in the third one.

I think the "test vm_file" thing may be unnecessary, because a
non-anonymous mapping should always have a file pointer and an inode.
But I could  imagine some odd case (vdso mapping, anyone?) that
doesn't have a vm_file, but also isn't anonymous.

Anybody?

Anyway, it's one reason why I didn't actually apply those other two
patches yet. This may be a 5.1 issue..

                   Linus