Messages in this thread | | | From | Linus Torvalds <> | Date | Mon, 7 Nov 2022 13:13:43 -0800 | Subject | Re: [PATCH] fs/userfaultfd: Fix maple tree iterator in userfaultfd_unregister() |
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On Mon, Nov 7, 2022 at 12:12 PM Liam Howlett <liam.howlett@oracle.com> wrote: > > When iterating the VMAs, the maple state needs to be invalidated if the > tree is modified by a split or merge to ensure the maple tree node > contained in the maple state is still valid. These invalidations were > missed, so add them to the paths which alter the tree.
I have applied this as an obvious fix, but I would *really* want to also see longer-term
- I'd really like the 'mas' operations to have 'vma' specializations that get the type safety right
- that mas_pause() name is horrible, please let's just fix it to something sensible in this context
- moving the iterator invalidation into split_vma() and vma_merge() or at least have some other means of not having these mistakes
From what I can tell, things like mprotect() and mlock() - end up not using the iterator at all because of this issue. Instead they seem to just do
vma = find_vma(current->mm, prev->vm_end);
despite having actually started out with the whole iterator state. Except for 'apply_mlockall_flags()' that randomly does end up usign the iterator (and has that mas_pause() as a result).
So it would make *sense* to have "mlock_fixup()" take a MA_STATE instead of "vma, &prev" as arguments, but it doesn't.
I dunno. Maybe there's some other reason for this very non-intuitive mix of "sometimes iterators, sometimes not, and always horrible naming".
Linus
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