Merge: mm/page_table_check: fix crash on ZONE_DEVICE

MR: https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-9/-/merge_requests/4767

Depends: !4749 

JIRA: https://issues.redhat.com/browse/RHEL-48052
CVE: CVE-2024-40948

Signed-off-by: Chris von Recklinghausen <crecklin@redhat.com>

Approved-by: Waiman Long <longman@redhat.com>
Approved-by: Rafael Aquini <raquini@redhat.com>
Approved-by: CKI KWF Bot <cki-ci-bot+kwf-gitlab-com@redhat.com>

Merged-by: Lucas Zampieri <lzampier@redhat.com>

Author: zampierilucas

mm/page_table_check.c

@@ -72,6 +72,9 @@ static void page_table_check_clear(struct mm_struct *mm, unsigned long addr,
 	page = pfn_to_page(pfn);
 	page_ext = page_ext_get(page);
 
+	if (!page_ext)
+		return;
+
 	BUG_ON(PageSlab(page));
 	anon = PageAnon(page);
 
@@ -110,6 +113,9 @@ static void page_table_check_set(struct mm_struct *mm, unsigned long addr,
 	page = pfn_to_page(pfn);
 	page_ext = page_ext_get(page);
 
+	if (!page_ext)
+		return;
+
 	BUG_ON(PageSlab(page));
 	anon = PageAnon(page);
 
@@ -140,7 +146,10 @@ void __page_table_check_zero(struct page *page, unsigned int order)
 	BUG_ON(PageSlab(page));
 
 	page_ext = page_ext_get(page);
-	BUG_ON(!page_ext);
+
+	if (!page_ext)
+		return;
+
 	for (i = 0; i < (1ul << order); i++) {
 		struct page_table_check *ptc = get_page_table_check(page_ext);