From bc17f2377818dca643a74499c3f5333500c90503 Mon Sep 17 00:00:00 2001 From: Waiman Long Date: Tue, 25 Jun 2024 20:16:39 -0400 Subject: [PATCH] mm: prevent derefencing NULL ptr in pfn_section_valid() [ Upstream commit 82f0b6f041fad768c28b4ad05a683065412c226e ] 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. Link: https://lkml.kernel.org/r/20240626001639.1350646-1-longman@redhat.com Fixes: 5ec8e8ea8b77 ("mm/sparsemem: fix race in accessing memory_section->usage") Signed-off-by: Waiman Long Cc: Charan Teja Kalla Signed-off-by: Andrew Morton Signed-off-by: Sasha Levin --- include/linux/mmzone.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index 8b8349ffa1cd..998f10249f13 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -1457,8 +1457,9 @@ 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)