The patch titled
Subject: mm: prevent derefencing NULL ptr in pfn_section_valid()
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-prevent-derefencing-null-ptr-in-pfn_section_valid.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-prevent-derefencing-null-ptr-in-pfn_section_valid.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Waiman Long <longman@xxxxxxxxxx>
Subject: mm: prevent derefencing NULL ptr in pfn_section_valid()
Date: Tue, 25 Jun 2024 20:16:39 -0400
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@xxxxxxxxxx
Fixes: 5ec8e8ea8b77 ("mm/sparsemem: fix race in accessing memory_section->usage")
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
Cc: Charan Teja Kalla <quic_charante@xxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/mmzone.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
--- a/include/linux/mmzone.h~mm-prevent-derefencing-null-ptr-in-pfn_section_valid
+++ a/include/linux/mmzone.h
@@ -1979,8 +1979,9 @@ static inline int subsection_map_index(u
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)
_
Patches currently in -mm which might be from longman@xxxxxxxxxx are
mm-prevent-derefencing-null-ptr-in-pfn_section_valid.patch
