On Thu, Feb 24, 2022 at 8:23 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > > On Thu, Feb 24, 2022 at 08:18:59PM -0800, Andrew Morton wrote: > > On Tue, 15 Feb 2022 12:19:22 -0800 Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote: > > > > > After exit_mmap frees all vmas in the mm, mm->mmap needs to be reset, > > > otherwise it points to a vma that was freed and when reused leads to > > > a use-after-free bug. > > > > > > ... > > > > > > --- a/mm/mmap.c > > > +++ b/mm/mmap.c > > > @@ -3186,6 +3186,7 @@ void exit_mmap(struct mm_struct *mm) > > > vma = remove_vma(vma); > > > cond_resched(); > > > } > > > + mm->mmap = NULL; > > > mmap_write_unlock(mm); > > > vm_unacct_memory(nr_accounted); > > > } > > > > After the Maple tree patches, mm_struct.mmap doesn't exist. So I'll > > revert this fix as part of merging the maple-tree parts of linux-next. > > I'll be sending this fix to Linus this week. > > > > All of which means that the thusly-resolved Maple tree patches might > > reintroduce this use-after-free bug. > > I don't think so? The problem is that VMAs are (currently) part of > two data structures -- the rbtree and the linked list. remove_vma() > only removes VMAs from the rbtree; it doesn't set mm->mmap to NULL. > > With maple tree, the linked list goes away. remove_vma() removes VMAs > from the maple tree. So anyone looking to iterate over all VMAs has to > go and look in the maple tree for them ... and there's nothing there. Yes, I think you are right. With maple trees we don't need this fix. > > But maybe I misunderstood the bug that's being solved here.
