Re: [PATCH v2] mm/migrate_device: fix pgtable leak in migrate_vma_insert_huge_pmd_page

["Huang, Ying" <ying.huang@linux.alibaba.com>]

Sunny Patel <nueralspacetech@gmail.com> writes:

> When migrate_vma_insert_huge_pmd_page() jumps to unlock_abort due
> to a PMD check failure, the pgtable allocated earlier via
> pte_alloc_one() is never freed, causing a memory leak.
>
> Add a pte_free() call in the unlock_abort error path to release
> the pgtable before returning.Also included before goto abort in the
> folio check path.
>
> Signed-off-by: Sunny Patel <nueralspacetech@gmail.com>
> ---
>
> Changes in v2:
>   - Added pte_free() before goto abort in the folio_is_zone_device()
>     check path. The lock is not taken at this point so goto unlock_abort would be incorrect here.
>   - v1 only fixed the unlock_abort path, this version fixes both
>     leak locations.
>
>  mm/migrate_device.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/mm/migrate_device.c b/mm/migrate_device.c
> index fbfe5715f635..7e132196856b 100644
> --- a/mm/migrate_device.c
> +++ b/mm/migrate_device.c
> @@ -840,6 +840,7 @@ static int migrate_vma_insert_huge_pmd_page(struct migrate_vma *migrate,
>  	} else {
>  		if (folio_is_zone_device(folio) &&
>  		    !folio_is_device_coherent(folio)) {
> +			pte_free(vma->vm_mm, pgtable);
>  			goto abort;

goto free_abort?

>  		}
>  		entry = folio_mk_pmd(folio, vma->vm_page_prot);
> @@ -893,6 +894,7 @@ static int migrate_vma_insert_huge_pmd_page(struct migrate_vma *migrate,
>  
>  unlock_abort:
>  	spin_unlock(ptl);

free_abort:

> +	pte_free(vma->vm_mm, pgtable);
>  abort:
>  	for (i = 0; i < HPAGE_PMD_NR; i++)
>  		src[i] &= ~MIGRATE_PFN_MIGRATE;

Although I prefer guard based memory freeing, if we stick with the
original error handling, I suggest following existing style more
closely.

---
Best Regards,
Huang, Ying