Commit faeec8e2 authored by David Hildenbrand's avatar David Hildenbrand Committed by Andrew Morton
Browse files

mm/page_alloc: don't call pfn_to_page() on possibly non-existent PFN in split_large_buddy() 

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.

Link: https://lkml.kernel.org/r/20241210093437.174413-1-david@redhat.com


Fixes: fd919a85 ("mm: page_isolation: prepare for hygienic freelists")
Signed-off-by: default avatarDavid Hildenbrand <david@redhat.com>
Reported-by: default avatarVlastimil Babka <vbabka@suse.cz>
Closes: https://lkml.kernel.org/r/e1a898ba-a717-4d20-9144-29df1a6c8813@suse.cz


Reviewed-by: default avatarVlastimil Babka <vbabka@suse.cz>
Reviewed-by: default avatarZi Yan <ziy@nvidia.com>
Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Cc: Yu Zhao <yuzhao@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 8ac662f5

mm/page_alloc.c

+4 −2
Original line number Diff line number Diff line
@@ -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,