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Subject[PATCH] slab: Add POISON_POINTER_DELTA to ZERO_SIZE_PTR
Date
POISON_POINTER_DELTA is defined in poison.h, and is intended to be used
to shift poison values so that they don't alias userspace.

We should add it to ZERO_SIZE_PTR so that attackers can't use
ZERO_SIZE_PTR as a way to get a pointer to userspace.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
---
include/linux/slab.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/slab.h b/include/linux/slab.h
index 084b12bad198..17ddd7aea2dd 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -12,6 +12,7 @@
#define _LINUX_SLAB_H

#include <linux/gfp.h>
+#include <linux/poison.h>
#include <linux/types.h>
#include <linux/workqueue.h>

@@ -109,7 +110,7 @@
* ZERO_SIZE_PTR can be passed to kfree though in the same way that NULL can.
* Both make kfree a no-op.
*/
-#define ZERO_SIZE_PTR ((void *)16)
+#define ZERO_SIZE_PTR ((void *)(16 + POISON_POINTER_DELTA))

#define ZERO_OR_NULL_PTR(x) ((unsigned long)(x) <= \
(unsigned long)ZERO_SIZE_PTR)
--
2.7.4
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