From: liqiong Date: Thu, 17 Feb 2022 11:54:16 +0000 (+0800) Subject: mm: fix dereference a null pointer in migrate[_huge]_page_move_mapping() X-Git-Tag: v4.19.236~37 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=deebce9df9ffaa62613bfcd8351d0c43a9a66108;p=thirdparty%2Fkernel%2Fstable.git 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: # linux-4.19.y Signed-off-by: liqiong Signed-off-by: Greg Kroah-Hartman --- diff --git a/mm/migrate.c b/mm/migrate.c index a69b842f95daf..76f8dedc0e02b 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -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 ||