mm/slub.c: init_on_free=1 should wipe freelist ptr for bulk allocations

slab_alloc_node() already zeroed out the freelist pointer if
init_on_free was on.  Thibaut Sautereau noticed that the same needs to
be done for kmem_cache_alloc_bulk(), which performs the allocations
separately.

kmem_cache_alloc_bulk() is currently used in two places in the kernel,
so this change is unlikely to have a major performance impact.

SLAB doesn't require a similar change, as auto-initialization makes the
allocator store the freelist pointers off-slab.

Link: http://lkml.kernel.org/r/20191007091605.30530-1-glider@google.com
Fixes: 6471384af2a6 ("mm: security: introduce init_on_alloc=1 and init_on_free=1 boot options")
Signed-off-by: Alexander Potapenko <glider@google.com>
Reported-by: Thibaut Sautereau <thibaut@sautereau.fr>
Reported-by: Kees Cook <keescook@chromium.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Laura Abbott <labbott@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 16 insertions, 6 deletions

diff --git a/mm/slub.c b/mm/slub.c
index 442f111d1e98..b25c807a111f 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2672,6 +2672,17 @@ static void *__slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
 }
 
 /*
+ * If the object has been wiped upon free, make sure it's fully initialized by
+ * zeroing out freelist pointer.
+ */
+static __always_inline void maybe_wipe_obj_freeptr(struct kmem_cache *s,
+                                                   void *obj)
+{
+        if (unlikely(slab_want_init_on_free(s)) && obj)
+                memset((void *)((char *)obj + s->offset), 0, sizeof(void *));
+}
+
+/*
  * Inlined fastpath so that allocation functions (kmalloc, kmem_cache_alloc)
  * have the fastpath folded into their functions. So no function call
  * overhead for requests that can be satisfied on the fastpath.
@@ -2759,12 +2770,8 @@ redo:
                 prefetch_freepointer(s, next_object);
                 stat(s, ALLOC_FASTPATH);
         }
-        /*
-         * If the object has been wiped upon free, make sure it's fully
-         * initialized by zeroing out freelist pointer.
-         */
-        if (unlikely(slab_want_init_on_free(s)) && object)
-                memset(object + s->offset, 0, sizeof(void *));
+
+        maybe_wipe_obj_freeptr(s, object);
 
         if (unlikely(slab_want_init_on_alloc(gfpflags, s)) && object)
                 memset(object, 0, s->object_size);
@@ -3178,10 +3185,13 @@ int kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t size,
                                 goto error;
 
                         c = this_cpu_ptr(s->cpu_slab);
+                        maybe_wipe_obj_freeptr(s, p[i]);
+
                         continue; /* goto for-loop */
                 }
                 c->freelist = get_freepointer(s, object);
                 p[i] = object;
+                maybe_wipe_obj_freeptr(s, p[i]);
         }
         c->tid = next_tid(c->tid);
         local_irq_enable();