From 04ad9908b0319210ef9e33775dd8a2adb0951586 Mon Sep 17 00:00:00 2001
From: Zi Yan <ziy@nvidia.com>
Date: Thu, 9 Jul 2026 14:06:04 -0400
Subject: [PATCH] mm/page_alloc: make sure tail_page->private is zero at page
 free time

Any code using tail_page->private of a folio, a compound page or a
high-order page is supposed to reset it after use, otherwise ->private
data can leak to new page user and cause unexpected issues.  Add a
bad_page() check at page free path for it.

Link: https://lore.kernel.org/20260709-keep-subpage-private-zero-at-free-v3-4-7e4fe155f5b9@nvidia.com
Signed-off-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Brendan Jackman <brendan.jackman@linux.dev>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nico Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
 mm/page_alloc.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index a63733dac659..cc45dfe89c76 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1377,15 +1377,23 @@ static __always_inline bool __free_pages_prepare(struct page *page,
 #endif
 		}
 		for (i = 1; i < (1 << order); i++) {
+			struct page *tail_page = page + i;
+
 			if (compound)
-				bad += free_tail_page_prepare(page, page + i);
+				bad += free_tail_page_prepare(page, tail_page);
 			if (is_check_pages_enabled()) {
-				if (free_page_is_bad(page + i)) {
+				if (free_page_is_bad(tail_page)) {
+					bad++;
+					continue;
+				}
+
+				if (tail_page->private) {
+					bad_page(tail_page, "nonzero private");
 					bad++;
 					continue;
 				}
 			}
-			(page + i)->flags.f &= ~PAGE_FLAGS_CHECK_AT_PREP;
+			tail_page->flags.f &= ~PAGE_FLAGS_CHECK_AT_PREP;
 		}
 	}
 	if (folio_test_anon(folio)) {