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

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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>
This commit is contained in:
liqiong 2022-02-17 19:54:16 +08:00 committed by Greg Kroah-Hartman
parent aa44002e7d
commit deebce9df9
1 changed files with 8 additions and 0 deletions
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8
mm/migrate.c
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@ -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 ||