Re: [PATCH] mm/mmap: Fix race in mmap_region() with ftrucate()

[Jann Horn]

On Tue, Oct 15, 2024 at 6:12 PM Liam R. Howlett <Liam.Howlett@xxxxxxxxxx> wrote:
> Avoiding the zeroing of the vma tree in mmap_region() introduced a race
> with truncate in the page table walk.  To avoid any races, create a hole
> in the rmap during the operation by clearing the pagetable entries
> earlier under the mmap write lock and (critically) before the new vma is
> installed into the vma tree.  The result is that the old vma is still in
> the vma tree, but the page tables are cleared while holding the
> i_mmap_rwsem.
>
> This change extends the fix required for hugetblfs and the call_mmap()
> function by moving the cleanup higher in the function and running it
> unconditionally.
>
> Cc: Jann Horn <jannh@xxxxxxxxxx>
> Cc: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
> Cc: Vlastimil Babka <vbabka@xxxxxxx>
> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Cc: David Hildenbrand <david@xxxxxxxxxx>
> Fixes: f8d112a4e657 ("mm/mmap: avoid zeroing vma tree in mmap_region()")
> Reported-by: Jann Horn <jannh@xxxxxxxxxx>
> Closes: https://lore.kernel.org/all/CAG48ez0ZpGzxi=-5O_uGQ0xKXOmbjeQ0LjZsRJ1Qtf2X5eOr1w@xxxxxxxxxxxxxx/
> Link: https://lore.kernel.org/all/CAG48ez0ZpGzxi=-5O_uGQ0xKXOmbjeQ0LjZsRJ1Qtf2X5eOr1w@xxxxxxxxxxxxxx/
> Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>

Thanks, this looks good to me.

Reviewed-by: Jann Horn <jannh@xxxxxxxxxx>