mm: SLAB hardened usercopy support

Under CONFIG_HARDENED_USERCOPY, this adds object size checking to the
SLAB allocator to catch any copies that may span objects.

Based on code from PaX and grsecurity.

Signed-off-by: Kees Cook <keescook@chromium.org>
Tested-by: Valdis Kletnieks <valdis.kletnieks@vt.edu>

diff --git a/init/Kconfig b/init/Kconfig
index c02d89777713b8772e47c2759570f4a838cb18e7..1312d7b5a5fb7e24387df24d557fe348b3946562 100644 (file)
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1758,6 +1758,7 @@ choice
 
 config SLAB
        bool "SLAB"
+       select HAVE_HARDENED_USERCOPY_ALLOCATOR
        help
          The regular slab allocator that is established and known to work
          well in all environments. It organizes cache hot objects in

diff --git a/mm/slab.c b/mm/slab.c
index cc8bbc1e6bc9b6fe5d980ffe3837d7b4c8843d84..5e2d5f349aca1142999e8bf22fea48a4ffde8b69 100644 (file)
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -4477,6 +4477,36 @@ static int __init slab_proc_init(void)
 module_init(slab_proc_init);
 #endif
 
+#ifdef CONFIG_HARDENED_USERCOPY
+/*
+ * Rejects objects that are incorrectly sized.
+ *
+ * Returns NULL if check passes, otherwise const char * to name of cache
+ * to indicate an error.
+ */
+const char *__check_heap_object(const void *ptr, unsigned long n,
+                               struct page *page)
+{
+       struct kmem_cache *cachep;
+       unsigned int objnr;
+       unsigned long offset;
+
+       /* Find and validate object. */
+       cachep = page->slab_cache;
+       objnr = obj_to_index(cachep, page, (void *)ptr);
+       BUG_ON(objnr >= cachep->num);
+
+       /* Find offset within object. */
+       offset = ptr - index_to_obj(cachep, page, objnr) - obj_offset(cachep);
+
+       /* Allow address range falling entirely within object size. */
+       if (offset <= cachep->object_size && n <= cachep->object_size - offset)
+               return NULL;
+
+       return cachep->name;
+}
+#endif /* CONFIG_HARDENED_USERCOPY */
+
 /**
  * ksize - get the actual amount of memory allocated for a given object
  * @objp: Pointer to the object