Commit 4d176711 authored by Andrey Konovalov's avatar Andrey Konovalov Committed by Linus Torvalds
Browse files

kasan: preassign tags to objects with ctors or SLAB_TYPESAFE_BY_RCU

An object constructor can initialize pointers within this objects based on
the address of the object.  Since the object address might be tagged, we
need to assign a tag before calling constructor.

The implemented approach is to assign tags to objects with constructors
when a slab is allocated and call constructors once as usual.  The
downside is that such object would always have the same tag when it is
reallocated, so we won't catch use-after-frees on it.

Also pressign tags for objects from SLAB_TYPESAFE_BY_RCU caches, since
they can be validy accessed after having been freed.


Signed-off-by: default avatarAndrey Konovalov <>
Reviewed-by: default avatarAndrey Ryabinin <>
Reviewed-by: default avatarDmitry Vyukov <>
Cc: Christoph Lameter <>
Cc: Mark Rutland <>
Cc: Will Deacon <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent e71fe3f9
......@@ -2574,7 +2574,7 @@ static void cache_init_objs(struct kmem_cache *cachep,
for (i = 0; i < cachep->num; i++) {
objp = index_to_obj(cachep, page, i);
kasan_init_slab_obj(cachep, objp);
objp = kasan_init_slab_obj(cachep, objp);
/* constructor could break poison info */
if (DEBUG == 0 && cachep->ctor) {
......@@ -1451,16 +1451,17 @@ static inline bool slab_free_freelist_hook(struct kmem_cache *s,
static void setup_object(struct kmem_cache *s, struct page *page,
static void *setup_object(struct kmem_cache *s, struct page *page,
void *object)
setup_object_debug(s, page, object);
kasan_init_slab_obj(s, object);
object = kasan_init_slab_obj(s, object);
if (unlikely(s->ctor)) {
kasan_unpoison_object_data(s, object);
kasan_poison_object_data(s, object);
return object;
......@@ -1568,16 +1569,16 @@ static bool shuffle_freelist(struct kmem_cache *s, struct page *page)
/* First entry is used as the base of the freelist */
cur = next_freelist_entry(s, page, &pos, start, page_limit,
cur = setup_object(s, page, cur);
page->freelist = cur;
for (idx = 1; idx < page->objects; idx++) {
setup_object(s, page, cur);
next = next_freelist_entry(s, page, &pos, start, page_limit,
next = setup_object(s, page, next);
set_freepointer(s, cur, next);
cur = next;
setup_object(s, page, cur);
set_freepointer(s, cur, NULL);
return true;
......@@ -1599,7 +1600,7 @@ static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node)
struct page *page;
struct kmem_cache_order_objects oo = s->oo;
gfp_t alloc_gfp;
void *start, *p;
void *start, *p, *next;
int idx, order;
bool shuffle;
......@@ -1651,13 +1652,16 @@ static struct page *allocate_slab(struct kmem_cache *s, gfp_t flags, int node)
if (!shuffle) {
for_each_object_idx(p, idx, s, start, page->objects) {
setup_object(s, page, p);
if (likely(idx < page->objects))
set_freepointer(s, p, p + s->size);
if (likely(idx < page->objects)) {
next = p + s->size;
next = setup_object(s, page, next);
set_freepointer(s, p, next);
} else
set_freepointer(s, p, NULL);
page->freelist = fixup_red_left(s, start);
start = fixup_red_left(s, start);
start = setup_object(s, page, start);
page->freelist = start;
page->inuse = page->objects;
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