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mm: prevent derefencing NULL ptr in pfn_section_valid()

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[ Upstream commit 82f0b6f041 ]

Commit 5ec8e8ea8b ("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: 5ec8e8ea8b ("mm/sparsemem: fix race in accessing memory_section->usage")
Signed-off-by: Waiman Long <longman@redhat.com>
Cc: Charan Teja Kalla <quic_charante@quicinc.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Waiman Long 2024-06-25 20:16:39 -04:00 committed by Greg Kroah-Hartman
parent fc19e23168
commit 797323d1cf
1 changed files with 2 additions and 1 deletions
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3
include/linux/mmzone.h
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@ -1968,8 +1968,9 @@ 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)