Re: [PATCH] mm/mincore: allow for making sys_mincore() privileged

[Linus Torvalds]

On Thu, Jan 24, 2019 at 9:27 AM Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> 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