linux-kernel - [patch] slob: fix memory corruption

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Message-ID: <20071115113204.GA24463@elte.hu>
Date:	Thu, 15 Nov 2007 12:32:04 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	David Miller <davem@...emloft.net>, mpm@...enic.com, rjw@...k.pl,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	torvalds@...ux-foundation.org, Thomas Gleixner <tglx@...utronix.de>
Subject: [patch] slob: fix memory corruption


* Ingo Molnar <mingo@...e.hu> wrote:

> > I had implemented SLOB in userspace, so I resynched and think I 
> > found your problem. Sorry for the attachment format -- this mailer 
> > isn't the best. I'm really computer illiterate when it comes to 
> > userspace...
> 
> thx, i'll try your fix in a minute.

that did the trick! Nick, find an updated patch below. (reference to the 
bugzilla added.)

	Ingo

-------------------->
Subject: slob: fix memory corruption
From: Nick Piggin <npiggin@...e.de>

Previously, it would be possible for prev->next to point to
&free_slob_pages, and thus we would try to move a list onto itself, and
bad things would happen.

It seems a bit hairy to be doing list operations with the list marker as
an entry, rather than a head, but...

this resolves the following crash:

  http://bugzilla.kernel.org/show_bug.cgi?id=9379

Signed-off-by: Nick Piggin <npiggin@...e.de>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 mm/slob.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Index: linux/mm/slob.c
===================================================================
--- linux.orig/mm/slob.c
+++ linux/mm/slob.c
@@ -321,7 +321,8 @@ static void *slob_alloc(size_t size, gfp
 		/* Improve fragment distribution and reduce our average
 		 * search time by starting our next search here. (see
 		 * Knuth vol 1, sec 2.5, pg 449) */
-		if (free_slob_pages.next != prev->next)
+		if (prev != free_slob_pages.prev &&
+				free_slob_pages.next != prev->next)
 			list_move_tail(&free_slob_pages, prev->next);
 		break;
 	}
-
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