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Commit 0f181f9f authored by Alexander Potapenko's avatar Alexander Potapenko Committed by Linus Torvalds
Browse files

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: 6471384a ("mm: security: introduce init_on_alloc=1 and init_on_free=1 boot options")
Signed-off-by: default avatarAlexander Potapenko <glider@google.com>
Reported-by: default avatarThibaut Sautereau <thibaut@sautereau.fr>
Reported-by: default avatarKees Cook <keescook@chromium.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Laura Abbott <labbott@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 3c52b0af

mm/slub.c

+16 −6
Original line number Diff line number Diff line
@@ -2671,6 +2671,17 @@ 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
@@ -2759,12 +2770,8 @@ 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);
@@ -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();