Re: [PATCH] kernel buffer overflow kmalloc_slab() fix

[Christoph Lameter <cl@linux.com>]

Subject: slub: Deal with hyperthetical case of PAGE_SIZE > 2M

kmalloc_index() currently returns -1 if the PAGE_SIZE is larger than 2M
which seems to cause some concern since the callers do not check for -1.

Insert a BUG() and add a comment to the -1 explaining that the code
cannot be reached.

Signed-off-by: Christoph Lameter <cl@linux.com>

---
 include/linux/slub_def.h |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

Index: linux-2.6/include/linux/slub_def.h
===================================================================
--- linux-2.6.orig/include/linux/slub_def.h	2011-05-20 09:37:02.000000000 -0500
+++ linux-2.6/include/linux/slub_def.h	2011-05-20 09:39:07.000000000 -0500
@@ -179,7 +179,8 @@ static __always_inline int kmalloc_index
 	if (size <=   4 * 1024) return 12;
 /*
  * The following is only needed to support architectures with a larger page
- * size than 4k.
+ * size than 4k. We need to support 2 * PAGE_SIZE here. So for a 64k page
+ * size we would have to go up to 128k.
  */
 	if (size <=   8 * 1024) return 13;
 	if (size <=  16 * 1024) return 14;
@@ -190,7 +191,8 @@ static __always_inline int kmalloc_index
 	if (size <= 512 * 1024) return 19;
 	if (size <= 1024 * 1024) return 20;
 	if (size <=  2 * 1024 * 1024) return 21;
-	return -1;
+	BUG();
+	return -1; /* Will never be reached */

 /*
  * What we really wanted to do and cannot do because of compiler issues is:

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