linux-kernel - [patch] mm: vmscan fix mapping use after free

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Message-ID: <20100615054343.GE6138@laptop>
Date:	Tue, 15 Jun 2010 15:43:44 +1000
From:	Nick Piggin <npiggin@...e.de>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Rik van Riel <riel@...hat.com>, Dave Chinner <david@...morbit.com>,
	Mel Gorman <mel@....ul.ie>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
	Chris Mason <chris.mason@...cle.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Christoph Hellwig <hch@...radead.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: [patch] mm: vmscan fix mapping use after free

On Tue, Jun 15, 2010 at 03:12:42PM +1000, Nick Piggin wrote:
> > Once that page is unlocked, we can't touch *mapping - its inode can be
> > concurrently reclaimed.  Although I guess the technique in
> > handle_write_error() can be reused.
> 
> Nasty. That guy needs to be using lock_page_nosync().
--

Need lock_page_nosync here because we have no reference to the mapping when
taking the page lock.

Signed-off-by: Nick Piggin <npiggin@...e.de>

---
 mm/vmscan.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-2.6/mm/vmscan.c
===================================================================
--- linux-2.6.orig/mm/vmscan.c
+++ linux-2.6/mm/vmscan.c
@@ -296,7 +296,7 @@ static int may_write_to_queue(struct bac
 static void handle_write_error(struct address_space *mapping,
 				struct page *page, int error)
 {
-	lock_page(page);
+	lock_page_nosync(page);
 	if (page_mapping(page) == mapping)
 		mapping_set_error(mapping, error);
 	unlock_page(page);
--
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