mm: SLUB hardened usercopy support

Under CONFIG_HARDENED_USERCOPY, this adds object size checking to the
SLUB allocator to catch any copies that may span objects. Includes a
redzone handling fix discovered by Michael Ellerman.

Based on code from PaX and grsecurity.

Signed-off-by: Kees Cook <keescook@chromium.org>
Tested-by: Michael Ellerman <mpe@ellerman.id.au>
Reviwed-by: Laura Abbott <labbott@redhat.com>

diff --git a/init/Kconfig b/init/Kconfig
index 1312d7b..0c84706 100644 (file)
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1766,6 +1766,7 @@ config SLAB
 
 config SLUB
        bool "SLUB (Unqueued Allocator)"
+       select HAVE_HARDENED_USERCOPY_ALLOCATOR
        help
           SLUB is a slab allocator that minimizes cache line usage
           instead of managing queues of cached objects (SLAB approach).

diff --git a/mm/slub.c b/mm/slub.c
index 825ff45..256a8ef 100644 (file)
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3614,6 +3614,46 @@ void *__kmalloc_node(size_t size, gfp_t flags, int node)
 EXPORT_SYMBOL(__kmalloc_node);
 #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 *s;
+       unsigned long offset;
+       size_t object_size;
+
+       /* Find object and usable object size. */
+       s = page->slab_cache;
+       object_size = slab_ksize(s);
+
+       /* Reject impossible pointers. */
+       if (ptr < page_address(page))
+               return s->name;
+
+       /* Find offset within object. */
+       offset = (ptr - page_address(page)) % s->size;
+
+       /* Adjust for redzone and reject if within the redzone. */
+       if (kmem_cache_debug(s) && s->flags & SLAB_RED_ZONE) {
+               if (offset < s->red_left_pad)
+                       return s->name;
+               offset -= s->red_left_pad;
+       }
+
+       /* Allow address range falling entirely within object size. */
+       if (offset <= object_size && n <= object_size - offset)
+               return NULL;
+
+       return s->name;
+}
+#endif /* CONFIG_HARDENED_USERCOPY */
+
 static size_t __ksize(const void *object)
 {
        struct page *page;