@@ -2669,6 +2669,17 @@ static void *__slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
return p;
}
+/*
+ * 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
@@ -2757,12 +2768,8 @@ static __always_inline void *slab_alloc_node(struct kmem_cache *s,
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);
@@ -3176,10 +3183,13 @@ 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();
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. Reported-by: Thibaut Sautereau <thibaut@sautereau.fr> Reported-by: Kees Cook <keescook@chromium.org> Signed-off-by: Alexander Potapenko <glider@google.com> Fixes: 6471384af2a6 ("mm: security: introduce init_on_alloc=1 and init_on_free=1 boot options") To: Andrew Morton <akpm@linux-foundation.org> To: Christoph Lameter <cl@linux.com> Cc: Laura Abbott <labbott@redhat.com> Cc: linux-mm@kvack.org Cc: kernel-hardening@lists.openwall.com --- v2: - added a missing return type to maybe_wipe_obj_freeptr() (spotted by kbuild test robot <lkp@intel.com>) --- mm/slub.c | 22 ++++++++++++++++------ 1 file changed, 16 insertions(+), 6 deletions(-)