diff mbox series

mm: Prevent derefencing NULL ptr in pfn_section_valid()

Message ID 20240626001639.1350646-1-longman@redhat.com (mailing list archive)
State New
Headers show
Series mm: Prevent derefencing NULL ptr in pfn_section_valid() | expand

Commit Message

Waiman Long June 26, 2024, 12:16 a.m. UTC 
Commit 5ec8e8ea8b77 ("mm/sparsemem: fix race in accessing
memory_section->usage") changed pfn_section_valid() to add a READ_ONCE()
call around "ms->usage" to fix a race with section_deactivate() where
ms->usage can be cleared.  The READ_ONCE() call, by itself, is not enough
to prevent NULL pointer dereference.  We need to check its value before
dereferencing it.

Fixes: 5ec8e8ea8b77 ("mm/sparsemem: fix race in accessing memory_section->usage")
Signed-off-by: Waiman Long <longman@redhat.com>
---
 include/linux/mmzone.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
diff mbox series

Patch

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 8f9c9590a42c..b1dcf6ddb406 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1980,8 +1980,9 @@  static inline int subsection_map_index(unsigned long pfn)
 static inline int pfn_section_valid(struct mem_section *ms, unsigned long pfn)
 {
 	int idx = subsection_map_index(pfn);
+	struct mem_section_usage *usage = READ_ONCE(ms->usage);
 
-	return test_bit(idx, READ_ONCE(ms->usage)->subsection_map);
+	return usage ? test_bit(idx, usage->subsection_map) : 0;
 }
 #else
 static inline int pfn_section_valid(struct mem_section *ms, unsigned long pfn)