[PATCH v3 2/6] mm/migrate_device: Do not write past the end of the src_pfns array

migrate_device_range() and migrate_device_pfns() zero the tail entries
of a large folio without checking them against @npages:

	for (j = 1; j < nr; j++)
		src_pfns[i+j] = 0;

@nr comes from the folio, not from the array, so a folio that extends
past the end of the range being migrated writes beyond src_pfns[].
Callers size that array for @npages entries, so this corrupts whatever
follows it.

Bound the loop by @npages. The subsequent "i += j - 1" still terminates
the outer loop correctly: on a bounded exit j is @npages - i, leaving i
at @npages after the increment.

Reported-by: Sashiko <[email protected]>
Fixes: a30b48bf1b24 ("mm/migrate_device: implement THP migration of zone device pages")
Cc: Andrew Morton <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Zi Yan <[email protected]>
Cc: Baolin Wang <[email protected]>
Cc: Liam R. Howlett <[email protected]>
Cc: Nico Pache <[email protected]>
Cc: Ryan Roberts <[email protected]>
Cc: Dev Jain <[email protected]>
Cc: Barry Song <[email protected]>
Cc: Lance Yang <[email protected]>
Cc: Usama Arif <[email protected]>
Cc: Joshua Hahn <[email protected]>
Cc: Rakie Kim <[email protected]>
Cc: Byungchul Park <[email protected]>
Cc: Gregory Price <[email protected]>
Cc: Ying Huang <[email protected]>
Cc: Alistair Popple <[email protected]>
Cc: Balbir Singh <[email protected]>
Cc: Maarten Lankhorst <[email protected]>
Cc: Maxime Ripard <[email protected]>
Cc: Thomas Zimmermann <[email protected]>
Cc: David Airlie <[email protected]>
Cc: Simona Vetter <[email protected]>
Cc: Thomas Hellström <[email protected]>
Cc: Francois Dugast <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Assisted-by: GitHub_Copilot:claude-opus-5
Signed-off-by: Matthew Brost <[email protected]>
---
 mm/migrate_device.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/migrate_device.c b/mm/migrate_device.c
index 162d29b2807a..ae9027421b80 100644
--- a/mm/migrate_device.c
+++ b/mm/migrate_device.c
@@ -1415,7 +1415,7 @@ int migrate_device_range(unsigned long *src_pfns, unsigned long start,
 		nr = folio_nr_pages(folio);
 		if (nr > 1) {
 			src_pfns[i] |= MIGRATE_PFN_COMPOUND;
-			for (j = 1; j < nr; j++)
+			for (j = 1; j < nr && (i + j) < npages; j++)
 				src_pfns[i+j] = 0;
 			i += j - 1;
 			pfn += j - 1;
@@ -1449,7 +1449,7 @@ int migrate_device_pfns(unsigned long *src_pfns, unsigned long npages)
 		nr = folio_nr_pages(folio);
 		if (nr > 1) {
 			src_pfns[i] |= MIGRATE_PFN_COMPOUND;
-			for (j = 1; j < nr; j++)
+			for (j = 1; j < nr && (i + j) < npages; j++)
 				src_pfns[i+j] = 0;
 			i += j - 1;
 		}
-- 
2.34.1