slab: Generify kernel pointer validation

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@linux-foundation.org>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Matt Mackall <mpm@selenic.com>
Cc: Nick Piggin <npiggin@suse.de>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 22 insertions, 12 deletions

diff --git a/mm/slab.c b/mm/slab.c
index a9f325b28bed..bac0f4fcc216 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 834db7be240f..f5712e8964be 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