linux-kernel - [PATCH 2/2] mm: fix NULL ptr dereference in move

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Date:	Fri, 13 Apr 2012 08:58:22 -0400
From:	Sasha Levin <levinsasha928@...il.com>
To:	cl@...ux.com, akpm@...ux-foundation.org
Cc:	hughd@...gle.com, dave@...ux.vnet.ibm.com, ebiederm@...ssion.com,
	davej@...hat.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Sasha Levin <levinsasha928@...il.com>
Subject: [PATCH 2/2] mm: fix NULL ptr dereference in move_pages

Commit 3268c63 ("mm: fix move/migrate_pages() race on task struct") has added
an odd construct where 'mm' is checked for being NULL, and if it is, it would
get dereferenced anyways by mput()ing it.

Signed-off-by: Sasha Levin <levinsasha928@...il.com>
---
 mm/migrate.c |   16 ++++++++--------
 1 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 51c08a0..1107238 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1388,14 +1388,14 @@ SYSCALL_DEFINE6(move_pages, pid_t, pid, unsigned long, nr_pages,
 	mm = get_task_mm(task);
 	put_task_struct(task);
 
-	if (mm) {
-		if (nodes)
-			err = do_pages_move(mm, task_nodes, nr_pages, pages,
-					    nodes, status, flags);
-		else
-			err = do_pages_stat(mm, nr_pages, pages, status);
-	} else
-		err = -EINVAL;
+	if (!mm)
+		return -EINVAL;
+
+	if (nodes)
+		err = do_pages_move(mm, task_nodes, nr_pages, pages,
+				    nodes, status, flags);
+	else
+		err = do_pages_stat(mm, nr_pages, pages, status);
 
 	mmput(mm);
 	return err;
-- 
1.7.8.5

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