Commit deebce9d authored Feb 17, 2022 by liqiong Committed by Greg Kroah-Hartman Mar 23, 2022

mm: fix dereference a null pointer in migrate[_huge]_page_move_mapping()



Upstream doesn't use radix tree any more in migrate.c, no need this patch.

The two functions look up a slot and dereference the pointer,
If the pointer is null, the kernel would crash and dump.

The 'numad' service calls 'migrate_pages' periodically. If some slots
being replaced (Cache Eviction), the radix_tree_lookup_slot() returns
a null pointer that causes kernel crash.

"numad":  crash> bt
[exception RIP: migrate_page_move_mapping+337]

Introduce pointer checking to avoid dereference a null pointer.

Cc: <stable@vger.kernel.org> # linux-4.19.y
Signed-off-by: liqiong <liqiong@nfschina.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent aa44002e

mm/migrate.c

+8 −0

Original line number	Diff line number	Diff line
		@@ -472,6 +472,10 @@ int migrate_page_move_mapping(struct address_space *mapping,

		pslot = radix_tree_lookup_slot(&mapping->i_pages,
		page_index(page));
		if (pslot == NULL) {
		xa_unlock_irq(&mapping->i_pages);
		return -EAGAIN;
		}

		expected_count += hpage_nr_pages(page) + page_has_private(page);
		if (page_count(page) != expected_count \|\|
		@@ -590,6 +594,10 @@ int migrate_huge_page_move_mapping(struct address_space *mapping,
		xa_lock_irq(&mapping->i_pages);

		pslot = radix_tree_lookup_slot(&mapping->i_pages, page_index(page));
		if (pslot == NULL) {
		xa_unlock_irq(&mapping->i_pages);
		return -EAGAIN;
		}

		expected_count = 2 + page_has_private(page);
		if (page_count(page) != expected_count \|\|