On 12/10/24 10:34, David Hildenbrand wrote:

In split_large_buddy(), we might call pfn_to_page() on a PFN that might not exist. In corner cases, such as when freeing the highest pageblock in the last memory section, this could result with CONFIG_SPARSEMEM && !CONFIG_SPARSEMEM_EXTREME in __pfn_to_section() returning NULL and and __section_mem_map_addr() dereferencing that NULL pointer.

Let's fix it, and avoid doing a pfn_to_page() call for the first iteration, where we already have the page.

So far this was found by code inspection, but let's just CC stable as the fix is easy.

Fixes: fd919a85cd55 ("mm: page_isolation: prepare for hygienic freelists") Reported-by: Vlastimil Babka vbabka@suse.cz Closes: https://lkml.kernel.org/r/e1a898ba-a717-4d20-9144-29df1a6c8813@suse.cz Cc: Andrew Morton akpm@linux-foundation.org Cc: Johannes Weiner hannes@cmpxchg.org Cc: Zi Yan ziy@nvidia.com Cc: Yu Zhao yuzhao@google.com Cc: stable@vger.kernel.org Signed-off-by: David Hildenbrand david@redhat.com

Reviewed-by: Vlastimil Babka vbabka@suse.cz

Thanks!

---

mm/page_alloc.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 48a291c485df4..a52c6022c65cb 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1238,13 +1238,15 @@ static void split_large_buddy(struct zone *zone, struct page *page, if (order > pageblock_order) order = pageblock_order;

• while (pfn != end) {

• do { int mt = get_pfnblock_migratetype(page, pfn);

__free_one_page(page, pfn, zone, order, mt, fpi); pfn += 1 << order;

• if (pfn == end)
  

• 	break;
  

  page = pfn_to_page(pfn);

• }

• } while (1);

} static void free_one_page(struct zone *zone, struct page *page,