From 8285027fc479949a7a166bc1b26ce57e894878a7 Mon Sep 17 00:00:00 2001
From: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
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: f86e4271978b ("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 <sudip.mukherjee@codethink.co.uk>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
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 c6cda3e36212..fedeba88c9cb 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");
--
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