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Subject[PATCH v2 3/3] kasan: fix krealloc handling for tag-based mode
Date
Right now tag-based KASAN can retag the memory that is reallocated via
krealloc and return a differently tagged pointer even if the same slab
object gets used and no reallocated technically happens.

There are a few issues with this approach. One is that krealloc callers
can't rely on comparing the return value with the passed argument to
check whether reallocation happened. Another is that if a caller knows
that no reallocation happened, that it can access object memory through
the old pointer, which leads to false positives. Look at nf_ct_ext_add()
to see an example.

Fix this by keeping the same tag if the memory don't actually gets
reallocated during krealloc.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
include/linux/kasan.h | 14 +++++---------
include/linux/slab.h | 4 ++--
mm/kasan/common.c | 20 ++++++++++++--------
mm/slab.c | 8 ++++----
mm/slab_common.c | 2 +-
mm/slub.c | 10 +++++-----
6 files changed, 29 insertions(+), 29 deletions(-)

diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index b40ea104dd36..7576fff90923 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -57,9 +57,8 @@ void * __must_check kasan_kmalloc_large(const void *ptr, size_t size,
void kasan_kfree_large(void *ptr, unsigned long ip);
void kasan_poison_kfree(void *ptr, unsigned long ip);
void * __must_check kasan_kmalloc(struct kmem_cache *s, const void *object,
- size_t size, gfp_t flags);
-void * __must_check kasan_krealloc(const void *object, size_t new_size,
- gfp_t flags);
+ size_t size, gfp_t flags, bool krealloc);
+void kasan_krealloc(const void *object, size_t new_size, gfp_t flags);

void * __must_check kasan_slab_alloc(struct kmem_cache *s, void *object,
gfp_t flags);
@@ -118,15 +117,12 @@ static inline void *kasan_kmalloc_large(void *ptr, size_t size, gfp_t flags)
static inline void kasan_kfree_large(void *ptr, unsigned long ip) {}
static inline void kasan_poison_kfree(void *ptr, unsigned long ip) {}
static inline void *kasan_kmalloc(struct kmem_cache *s, const void *object,
- size_t size, gfp_t flags)
-{
- return (void *)object;
-}
-static inline void *kasan_krealloc(const void *object, size_t new_size,
- gfp_t flags)
+ size_t size, gfp_t flags, bool krealloc)
{
return (void *)object;
}
+static inline void kasan_krealloc(const void *object, size_t new_size,
+ gfp_t flags) {}

static inline void *kasan_slab_alloc(struct kmem_cache *s, void *object,
gfp_t flags)
diff --git a/include/linux/slab.h b/include/linux/slab.h
index d87f913ab4e8..1cd168758c05 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -445,7 +445,7 @@ static __always_inline void *kmem_cache_alloc_trace(struct kmem_cache *s,
{
void *ret = kmem_cache_alloc(s, flags);

- ret = kasan_kmalloc(s, ret, size, flags);
+ ret = kasan_kmalloc(s, ret, size, flags, false);
return ret;
}

@@ -456,7 +456,7 @@ kmem_cache_alloc_node_trace(struct kmem_cache *s,
{
void *ret = kmem_cache_alloc_node(s, gfpflags, node);

- ret = kasan_kmalloc(s, ret, size, gfpflags);
+ ret = kasan_kmalloc(s, ret, size, gfpflags, false);
return ret;
}
#endif /* CONFIG_TRACING */
diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 44390392d4c9..b6633ab86160 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -392,7 +392,7 @@ void * __must_check kasan_init_slab_obj(struct kmem_cache *cache,
void * __must_check kasan_slab_alloc(struct kmem_cache *cache, void *object,
gfp_t flags)
{
- return kasan_kmalloc(cache, object, cache->object_size, flags);
+ return kasan_kmalloc(cache, object, cache->object_size, flags, false);
}

static inline bool shadow_invalid(u8 tag, s8 shadow_byte)
@@ -451,7 +451,7 @@ bool kasan_slab_free(struct kmem_cache *cache, void *object, unsigned long ip)
}

void * __must_check kasan_kmalloc(struct kmem_cache *cache, const void *object,
- size_t size, gfp_t flags)
+ size_t size, gfp_t flags, bool krealloc)
{
unsigned long redzone_start;
unsigned long redzone_end;
@@ -468,8 +468,12 @@ void * __must_check kasan_kmalloc(struct kmem_cache *cache, const void *object,
redzone_end = round_up((unsigned long)object + cache->object_size,
KASAN_SHADOW_SCALE_SIZE);

- if (IS_ENABLED(CONFIG_KASAN_SW_TAGS))
- tag = assign_tag(cache, object, false);
+ if (IS_ENABLED(CONFIG_KASAN_SW_TAGS)) {
+ if (krealloc)
+ tag = get_tag(object);
+ else
+ tag = assign_tag(cache, object, false);
+ }

/* Tag is ignored in set_tag without CONFIG_KASAN_SW_TAGS */
kasan_unpoison_shadow(set_tag(object, tag), size);
@@ -508,19 +512,19 @@ void * __must_check kasan_kmalloc_large(const void *ptr, size_t size,
return (void *)ptr;
}

-void * __must_check kasan_krealloc(const void *object, size_t size, gfp_t flags)
+void kasan_krealloc(const void *object, size_t size, gfp_t flags)
{
struct page *page;

if (unlikely(object == ZERO_SIZE_PTR))
- return (void *)object;
+ return;

page = virt_to_head_page(object);

if (unlikely(!PageSlab(page)))
- return kasan_kmalloc_large(object, size, flags);
+ kasan_kmalloc_large(object, size, flags);
else
- return kasan_kmalloc(page->slab_cache, object, size, flags);
+ kasan_kmalloc(page->slab_cache, object, size, flags, true);
}

void kasan_poison_kfree(void *ptr, unsigned long ip)
diff --git a/mm/slab.c b/mm/slab.c
index 73fe23e649c9..09b54386cf67 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -3604,7 +3604,7 @@ kmem_cache_alloc_trace(struct kmem_cache *cachep, gfp_t flags, size_t size)

ret = slab_alloc(cachep, flags, _RET_IP_);

- ret = kasan_kmalloc(cachep, ret, size, flags);
+ ret = kasan_kmalloc(cachep, ret, size, flags, false);
trace_kmalloc(_RET_IP_, ret,
size, cachep->size, flags);
return ret;
@@ -3647,7 +3647,7 @@ void *kmem_cache_alloc_node_trace(struct kmem_cache *cachep,

ret = slab_alloc_node(cachep, flags, nodeid, _RET_IP_);

- ret = kasan_kmalloc(cachep, ret, size, flags);
+ ret = kasan_kmalloc(cachep, ret, size, flags, false);
trace_kmalloc_node(_RET_IP_, ret,
size, cachep->size,
flags, nodeid);
@@ -3668,7 +3668,7 @@ __do_kmalloc_node(size_t size, gfp_t flags, int node, unsigned long caller)
if (unlikely(ZERO_OR_NULL_PTR(cachep)))
return cachep;
ret = kmem_cache_alloc_node_trace(cachep, flags, node, size);
- ret = kasan_kmalloc(cachep, ret, size, flags);
+ ret = kasan_kmalloc(cachep, ret, size, flags, false);

return ret;
}
@@ -3706,7 +3706,7 @@ static __always_inline void *__do_kmalloc(size_t size, gfp_t flags,
return cachep;
ret = slab_alloc(cachep, flags, caller);

- ret = kasan_kmalloc(cachep, ret, size, flags);
+ ret = kasan_kmalloc(cachep, ret, size, flags, false);
trace_kmalloc(caller, ret,
size, cachep->size, flags);

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 81732d05e74a..b55c58178f83 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1507,7 +1507,7 @@ static __always_inline void *__do_krealloc(const void *p, size_t new_size,
ks = ksize(p);

if (ks >= new_size) {
- p = kasan_krealloc((void *)p, new_size, flags);
+ kasan_krealloc((void *)p, new_size, flags);
return (void *)p;
}

diff --git a/mm/slub.c b/mm/slub.c
index 1e3d0ec4e200..20aa0547acbf 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2763,7 +2763,7 @@ void *kmem_cache_alloc_trace(struct kmem_cache *s, gfp_t gfpflags, size_t size)
{
void *ret = slab_alloc(s, gfpflags, _RET_IP_);
trace_kmalloc(_RET_IP_, ret, size, s->size, gfpflags);
- ret = kasan_kmalloc(s, ret, size, gfpflags);
+ ret = kasan_kmalloc(s, ret, size, gfpflags, false);
return ret;
}
EXPORT_SYMBOL(kmem_cache_alloc_trace);
@@ -2791,7 +2791,7 @@ void *kmem_cache_alloc_node_trace(struct kmem_cache *s,
trace_kmalloc_node(_RET_IP_, ret,
size, s->size, gfpflags, node);

- ret = kasan_kmalloc(s, ret, size, gfpflags);
+ ret = kasan_kmalloc(s, ret, size, gfpflags, false);
return ret;
}
EXPORT_SYMBOL(kmem_cache_alloc_node_trace);
@@ -3364,7 +3364,7 @@ static void early_kmem_cache_node_alloc(int node)
init_tracking(kmem_cache_node, n);
#endif
n = kasan_kmalloc(kmem_cache_node, n, sizeof(struct kmem_cache_node),
- GFP_KERNEL);
+ GFP_KERNEL, false);
page->freelist = get_freepointer(kmem_cache_node, n);
page->inuse = 1;
page->frozen = 0;
@@ -3779,7 +3779,7 @@ void *__kmalloc(size_t size, gfp_t flags)

trace_kmalloc(_RET_IP_, ret, size, s->size, flags);

- ret = kasan_kmalloc(s, ret, size, flags);
+ ret = kasan_kmalloc(s, ret, size, flags, false);

return ret;
}
@@ -3823,7 +3823,7 @@ void *__kmalloc_node(size_t size, gfp_t flags, int node)

trace_kmalloc_node(_RET_IP_, ret, size, s->size, flags, node);

- ret = kasan_kmalloc(s, ret, size, flags);
+ ret = kasan_kmalloc(s, ret, size, flags, false);

return ret;
}
--
2.20.1.415.g653613c723-goog
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