Re: [PATCH] mm/migrate: initialize pud_entry in migrate_vma()

[Vlastimil Babka]

On 7/20/19 1:32 AM, Ralph Campbell wrote:
> When CONFIG_MIGRATE_VMA_HELPER is enabled, migrate_vma() calls
> migrate_vma_collect() which initializes a struct mm_walk but
> didn't initialize mm_walk.pud_entry. (Found by code inspection)
> Use a C structure initialization to make sure it is set to NULL.
> 
> Fixes: 8763cb45ab967 ("mm/migrate: new memory migration helper for use with
> device memory")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Ralph Campbell <rcampbell@xxxxxxxxxx>
> Cc: "JÃrÃme Glisse" <jglisse@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>

So this bug can manifest by some garbage address on stack being called, right? I
wonder, how comes it didn't actually happen yet?

> ---
>  mm/migrate.c | 17 +++++++----------
>  1 file changed, 7 insertions(+), 10 deletions(-)
> 
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 515718392b24..a42858d8e00b 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -2340,16 +2340,13 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
>  static void migrate_vma_collect(struct migrate_vma *migrate)
>  {
>  	struct mmu_notifier_range range;
> -	struct mm_walk mm_walk;
> -
> -	mm_walk.pmd_entry = migrate_vma_collect_pmd;
> -	mm_walk.pte_entry = NULL;
> -	mm_walk.pte_hole = migrate_vma_collect_hole;
> -	mm_walk.hugetlb_entry = NULL;
> -	mm_walk.test_walk = NULL;
> -	mm_walk.vma = migrate->vma;
> -	mm_walk.mm = migrate->vma->vm_mm;
> -	mm_walk.private = migrate;
> +	struct mm_walk mm_walk = {
> +		.pmd_entry = migrate_vma_collect_pmd,
> +		.pte_hole = migrate_vma_collect_hole,
> +		.vma = migrate->vma,
> +		.mm = migrate->vma->vm_mm,
> +		.private = migrate,
> +	};
>  
>  	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, NULL, mm_walk.mm,
>  				migrate->start,
>