From f6920c5b45ad326f28666c8c90599128f19c9edf Mon Sep 17 00:00:00 2001 From: Sudip Mukherjee Date: Fri, 24 Jun 2016 14:50:24 -0700 Subject: [PATCH] mm/page_owner: avoid null pointer dereference We have dereferenced page_ext before checking it. Lets check it first and then used it. Fixes: 99bde03cf0c2 ("mm: check the return value of lookup_page_ext for all call sites") Link: http://lkml.kernel.org/r/1465249059-7883-1-git-send-email-sudipm.mukherjee@gmail.com Signed-off-by: Sudip Mukherjee Acked-by: Vlastimil Babka Cc: Joonsoo Kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/page_owner.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/mm/page_owner.c b/mm/page_owner.c index c6cda3e362128..fedeba88c9cb8 100644 --- a/mm/page_owner.c +++ b/mm/page_owner.c @@ -207,13 +207,15 @@ void __dump_page_owner(struct page *page) .nr_entries = page_ext->nr_entries, .entries = &page_ext->trace_entries[0], }; - gfp_t gfp_mask = page_ext->gfp_mask; - int mt = gfpflags_to_migratetype(gfp_mask); + gfp_t gfp_mask; + int mt; if (unlikely(!page_ext)) { pr_alert("There is not page extension available.\n"); return; } + gfp_mask = page_ext->gfp_mask; + mt = gfpflags_to_migratetype(gfp_mask); if (!test_bit(PAGE_EXT_OWNER, &page_ext->flags)) { pr_alert("page_owner info is not active (free page?)\n"); -- 2.39.5