This is a note to let you know that I've just added the patch titled
mm: prevent derefencing NULL ptr in pfn_section_valid()
to the 5.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
mm-prevent-derefencing-null-ptr-in-pfn_section_valid.patch
and it can be found in the queue-5.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit fc7839b7839f0656af821ccd35ae6423c906a00f
Author: Waiman Long <longman@xxxxxxxxxx>
Date: Tue Jun 25 20:16:39 2024 -0400
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@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>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 8b8349ffa1cd9..998f10249f136 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)
