[PATCH 1/2] slab: Generify kernel pointer validation

[Pekka Enberg]

As suggested by Linus, introduce a kern_ptr_validate() helper that does some
sanity checks to make sure a pointer is a valid kernel pointer.  This is a
preparational step for fixing SLUB kmem_ptr_validate().

Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxxxxxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Matt Mackall <mpm@xxxxxxxxxxx>
Cc: Nick Piggin <npiggin@xxxxxxx>
Signed-off-by: Pekka Enberg <penberg@xxxxxxxxxxxxxx>
---
 include/linux/slab.h |    1 +
 mm/slab.c            |   13 +------------
 mm/util.c            |   21 +++++++++++++++++++++
 3 files changed, 23 insertions(+), 12 deletions(-)

diff --git a/include/linux/slab.h b/include/linux/slab.h
index 4884462..49d1247 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -106,6 +106,7 @@ int kmem_cache_shrink(struct kmem_cache *);
 void kmem_cache_free(struct kmem_cache *, void *);
 unsigned int kmem_cache_size(struct kmem_cache *);
 const char *kmem_cache_name(struct kmem_cache *);
+int kern_ptr_validate(const void *ptr, unsigned long size);
 int kmem_ptr_validate(struct kmem_cache *cachep, const void *ptr);
 
 /*
diff --git a/mm/slab.c b/mm/slab.c
index a9f325b..bac0f4f 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -3602,21 +3602,10 @@ EXPORT_SYMBOL(kmem_cache_alloc_notrace);
  */
 int kmem_ptr_validate(struct kmem_cache *cachep, const void *ptr)
 {
-	unsigned long addr = (unsigned long)ptr;
-	unsigned long min_addr = PAGE_OFFSET;
-	unsigned long align_mask = BYTES_PER_WORD - 1;
 	unsigned long size = cachep->buffer_size;
 	struct page *page;
 
-	if (unlikely(addr < min_addr))
-		goto out;
-	if (unlikely(addr > (unsigned long)high_memory - size))
-		goto out;
-	if (unlikely(addr & align_mask))
-		goto out;
-	if (unlikely(!kern_addr_valid(addr)))
-		goto out;
-	if (unlikely(!kern_addr_valid(addr + size - 1)))
+	if (unlikely(!kern_ptr_validate(ptr, size)))
 		goto out;
 	page = virt_to_page(ptr);
 	if (unlikely(!PageSlab(page)))
diff --git a/mm/util.c b/mm/util.c
index 834db7b..f5712e8 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -186,6 +186,27 @@ void kzfree(const void *p)
 }
 EXPORT_SYMBOL(kzfree);
 
+int kern_ptr_validate(const void *ptr, unsigned long size)
+{
+	unsigned long addr = (unsigned long)ptr;
+	unsigned long min_addr = PAGE_OFFSET;
+	unsigned long align_mask = sizeof(void *) - 1;
+
+	if (unlikely(addr < min_addr))
+		goto out;
+	if (unlikely(addr > (unsigned long)high_memory - size))
+		goto out;
+	if (unlikely(addr & align_mask))
+		goto out;
+	if (unlikely(!kern_addr_valid(addr)))
+		goto out;
+	if (unlikely(!kern_addr_valid(addr + size - 1)))
+		goto out;
+	return 1;
+out:
+	return 0;
+}
+
 /*
  * strndup_user - duplicate an existing string from user space
  * @s: The string to duplicate
-- 
1.6.3.3

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