linux-kernel - [PATCH] cache_k8_northbridges() overflows beyond allocation (Was: 2.6.21-rc5-mm4 (SLUB))

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Date:	Fri, 13 Apr 2007 08:13:42 -0700
From:	Badari Pulavarty <pbadari@...il.com>
To:	Christoph Lameter <clameter@....com>, ak@...e.de
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	lkml <linux-kernel@...r.kernel.org>
Subject: [PATCH] cache_k8_northbridges() overflows beyond allocation (Was:
	2.6.21-rc5-mm4 (SLUB))

On Wed, 2007-04-04 at 11:04 -0700, Christoph Lameter wrote:
> On Wed, 4 Apr 2007, Badari Pulavarty wrote:
...
> 
> > *** SLUB: Freepointer corrupt in kmalloc-16@...fff810173f172a0 Slab
> > 0xffff81017f9f8b80
> >     offset=672 flags=0x2000000000000c7 inuse=42
> > freelist=0xffff810173f172a0
> >   Bytes b4 0xffff810173f17290:  a0 72 f1 73 00 00 00 00 00 00 00 00 00
> > 00 00 00 .r\uffffs............
> >     Object 0xffff810173f172a0:  00 00 00 00 01 81 ff ff 00 00 00 00 00
> > 00 00 00 ......\uffff\uffff........
> > FreePointer 0xffff810173f172a0 -> 0xffff810100000000
> 

Found it !! After a painful capture of all the kmalloc-16 slab
allocations (400+) so far and auditing some of them, found the
culprit - who writes beyond its allocation, causing the slab
corruption.

Thanks,
Badari

cache_k8_northbridges() is storing config values to incorrect locations
(in flush_words) and also its overflowing beyond the allocation, causing
slab verification failures.

Signed-off-by: Badari Pulavarty <pbadari@...ibm.com>
---
 arch/x86_64/kernel/k8.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Index: linux-2.6.21-rc6/arch/x86_64/kernel/k8.c
===================================================================
--- linux-2.6.21-rc6.orig/arch/x86_64/kernel/k8.c	2007-04-05 19:36:56.000000000 -0700
+++ linux-2.6.21-rc6/arch/x86_64/kernel/k8.c	2007-04-13 07:51:57.000000000 -0700
@@ -61,8 +61,8 @@ int cache_k8_northbridges(void)
 	dev = NULL;
 	i = 0;
 	while ((dev = next_k8_northbridge(dev)) != NULL) {
-		k8_northbridges[i++] = dev;
-		pci_read_config_dword(dev, 0x9c, &flush_words[i]);
+		k8_northbridges[i] = dev;
+		pci_read_config_dword(dev, 0x9c, &flush_words[i++]);
 	}
 	k8_northbridges[i] = NULL;
 	return 0;


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