linux-kernel - [052/116] tmpfs: fix oops on mounts with mpol=default

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Message-Id: <20100330225631.818500832@linux.site>
Date:	Tue, 30 Mar 2010 15:55:30 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Ravikiran Thirumalai <kiran@...lex86.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>,
	Lee Schermerhorn <lee.schermerhorn@...com>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Greg Kroah-Hartman <gregkh@...e.de>
Subject: [052/116] tmpfs: fix oops on mounts with mpol=default

2.6.32-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Ravikiran G Thirumalai <kiran@...lex86.org>

commit 413b43deab8377819aba1dbad2abf0c15d59b491 upstream.

Fix an 'oops' when a tmpfs mount point is mounted with the mpol=default
mempolicy.

Upon remounting a tmpfs mount point with 'mpol=default' option, the mount
code crashed with a null pointer dereference.  The initial problem report
was on 2.6.27, but the problem exists in mainline 2.6.34-rc as well.  On
examining the code, we see that mpol_new returns NULL if default mempolicy
was requested.  This 'NULL' mempolicy is accessed to store the node mask
resulting in oops.

The following patch fixes it.

Signed-off-by: Ravikiran Thirumalai <kiran@...lex86.org>
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc: Christoph Lameter <cl@...ux-foundation.org>
Cc: Mel Gorman <mel@....ul.ie>
Acked-by: Lee Schermerhorn <lee.schermerhorn@...com>
Cc: Hugh Dickins <hugh.dickins@...cali.co.uk>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 mm/mempolicy.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2142,10 +2142,15 @@ int mpol_parse_str(char *str, struct mem
 			goto out;
 		mode = MPOL_PREFERRED;
 		break;
-
+	case MPOL_DEFAULT:
+		/*
+		 * Insist on a empty nodelist
+		 */
+		if (!nodelist)
+			err = 0;
+		goto out;
 	/*
 	 * case MPOL_BIND:    mpol_new() enforces non-empty nodemask.
-	 * case MPOL_DEFAULT: mpol_new() enforces empty nodemask, ignores flags.
 	 */
 	}
 


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