[PATCH] include/linux/kasan.h: Notice about 0 for kasan_[dis/en]able_current()

[PATCH] include/linux/kasan.h: Notice about 0 for kasan_[dis/en]able_current()

[chengang]

From: Chen Gang <chengang@emindsoft.com.cn>

According to their comments and the kasan_depth's initialization, if
kasan_depth is zero, it means disable. So kasan_depth need consider
about the 0 overflow.

Also remove useless comments for dummy kasan_slab_free().

Signed-off-by: Chen Gang <gang.chen.5i5j@gmail.com>
---
 include/linux/kasan.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/include/linux/kasan.h b/include/linux/kasan.h
index 645c280..37fab04 100644
--- a/include/linux/kasan.h
+++ b/include/linux/kasan.h
@@ -32,13 +32,15 @@ static inline void *kasan_mem_to_shadow(const void *addr)
 /* Enable reporting bugs after kasan_disable_current() */
 static inline void kasan_enable_current(void)
 {
-	current->kasan_depth++;
+	if (current->kasan_depth + 1)
+		current->kasan_depth++;
 }
 
 /* Disable reporting bugs for current task */
 static inline void kasan_disable_current(void)
 {
-	current->kasan_depth--;
+	if (current->kasan_depth)
+		current->kasan_depth--;
 }
 
 void kasan_unpoison_shadow(const void *address, size_t size);
@@ -113,8 +115,6 @@ static inline void kasan_krealloc(const void *object, size_t new_size,
 
 static inline void kasan_slab_alloc(struct kmem_cache *s, void *object,
 				   gfp_t flags) {}
-/* kasan_slab_free() returns true if the object has been put into quarantine.
- */
 static inline bool kasan_slab_free(struct kmem_cache *s, void *object)
 {
 	return false;
-- 
1.9.3

Re: [PATCH] include/linux/kasan.h: Notice about 0 for kasan_[dis/en]able_current()

[Alexander Potapenko]

On Mon, May 2, 2016 at 7:35 AM,  <chengang@emindsoft.com.cn> wrote:
> From: Chen Gang <chengang@emindsoft.com.cn>
>
> According to their comments and the kasan_depth's initialization, if
> kasan_depth is zero, it means disable. So kasan_depth need consider
> about the 0 overflow.
>
> Also remove useless comments for dummy kasan_slab_free().
>
> Signed-off-by: Chen Gang <gang.chen.5i5j@gmail.com>
> ---
>  include/linux/kasan.h | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index 645c280..37fab04 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -32,13 +32,15 @@ static inline void *kasan_mem_to_shadow(const void *addr)
>  /* Enable reporting bugs after kasan_disable_current() */
>  static inline void kasan_enable_current(void)
>  {
> -       current->kasan_depth++;
> +       if (current->kasan_depth + 1)
> +               current->kasan_depth++;
>  }
>
>  /* Disable reporting bugs for current task */
>  static inline void kasan_disable_current(void)
>  {
> -       current->kasan_depth--;
> +       if (current->kasan_depth)
> +               current->kasan_depth--;
>  }
>
>  void kasan_unpoison_shadow(const void *address, size_t size);
> @@ -113,8 +115,6 @@ static inline void kasan_krealloc(const void *object, size_t new_size,
>
>  static inline void kasan_slab_alloc(struct kmem_cache *s, void *object,
>                                    gfp_t flags) {}
> -/* kasan_slab_free() returns true if the object has been put into quarantine.
> - */
>  static inline bool kasan_slab_free(struct kmem_cache *s, void *object)
>  {
>         return false;
> --
> 1.9.3
>

Acked-by: Alexander Potapenko <glider@google.com>

-- 
Alexander Potapenko
Software Engineer

Google Germany GmbH
Erika-Mann-Straße, 33
80636 München

Geschäftsführer: Matthew Scott Sucherman, Paul Terence Manicle
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg

Re: [PATCH] include/linux/kasan.h: Notice about 0 for kasan_[dis/en]able_current()

[Chen Gang]

On 5/2/16 18:49, Alexander Potapenko wrote:
> On Mon, May 2, 2016 at 7:35 AM,  <chengang@emindsoft.com.cn> wrote:
>>
>> According to their comments and the kasan_depth's initialization, if
>> kasan_depth is zero, it means disable. So kasan_depth need consider
>> about the 0 overflow.
>>
>> Also remove useless comments for dummy kasan_slab_free().
>>
>> Signed-off-by: Chen Gang <gang.chen.5i5j@gmail.com>
> 
> Acked-by: Alexander Potapenko <glider@google.com>
> 

OK, thanks.

Another patch thread is also related with this patch thread, please help
check.

And sorry, originally, I did not let the 2 patches in one patches set.

Thanks.
-- 
Chen Gang (陈刚)

Managing Natural Environments is the Duty of Human Beings.

Re: [PATCH] include/linux/kasan.h: Notice about 0 for kasan_[dis/en]able_current()

[Alexander Potapenko]

On Mon, May 2, 2016 at 1:20 PM, Chen Gang <chengang@emindsoft.com.cn> wrote:
> On 5/2/16 18:49, Alexander Potapenko wrote:
>> On Mon, May 2, 2016 at 7:35 AM,  <chengang@emindsoft.com.cn> wrote:
>>>
>>> According to their comments and the kasan_depth's initialization, if
>>> kasan_depth is zero, it means disable. So kasan_depth need consider
>>> about the 0 overflow.
>>>
>>> Also remove useless comments for dummy kasan_slab_free().
>>>
>>> Signed-off-by: Chen Gang <gang.chen.5i5j@gmail.com>
>>
>> Acked-by: Alexander Potapenko <glider@google.com>
Nacked-by: Alexander Potapenko <glider@google.com>
>>
>
> OK, thanks.
Well, on a second thought I take that back, there still might be problems.
I haven't noticed the other CL, and was too hasty reviewing this one.

As kasan_disable_current() and kasan_enable_current() always go
together, we need to prevent nested calls to them from breaking
everything.
If we ignore some calls to kasan_disable_current() to prevent
overflows, the pairing calls to kasan_enable_current() will bring
|current->kasan_depth| to an invalid state.

E.g. if I'm understanding your idea correctly, after the following
sequence of calls:
  kasan_disable_current();  // #1
  kasan_disable_current();  // #2
  kasan_enable_current();  // #3
  kasan_enable_current();  // #4

the value of |current->kasan_depth| will be 2, so a single subsequent
call to kasan_disable_current() won't disable KASAN.

I think we'd better add BUG checks to bail out if the value of
|current->kasan_depth| is too big or too small.

> Another patch thread is also related with this patch thread, please help
> check.
>
> And sorry, originally, I did not let the 2 patches in one patches set.
>
> Thanks.
> --
> Chen Gang (陈刚)
>
> Managing Natural Environments is the Duty of Human Beings.



-- 
Alexander Potapenko
Software Engineer

Google Germany GmbH
Erika-Mann-Straße, 33
80636 München

Geschäftsführer: Matthew Scott Sucherman, Paul Terence Manicle
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg

Re: [PATCH] include/linux/kasan.h: Notice about 0 for kasan_[dis/en]able_current()

[Chen Gang]

On 5/2/16 19:23, Alexander Potapenko wrote:
> On Mon, May 2, 2016 at 1:20 PM, Chen Gang <chengang@emindsoft.com.cn> wrote:
>> On 5/2/16 18:49, Alexander Potapenko wrote:
>>> On Mon, May 2, 2016 at 7:35 AM,  <chengang@emindsoft.com.cn> wrote:
>>>>
>>>> According to their comments and the kasan_depth's initialization, if
>>>> kasan_depth is zero, it means disable. So kasan_depth need consider
>>>> about the 0 overflow.
>>>>
>>>> Also remove useless comments for dummy kasan_slab_free().
>>>>
>>>> Signed-off-by: Chen Gang <gang.chen.5i5j@gmail.com>
>>>
>>> Acked-by: Alexander Potapenko <glider@google.com>
> Nacked-by: Alexander Potapenko <glider@google.com>
>>>
>>
>> OK, thanks.
> Well, on a second thought I take that back, there still might be problems.
> I haven't noticed the other CL, and was too hasty reviewing this one.
> 
> As kasan_disable_current() and kasan_enable_current() always go
> together, we need to prevent nested calls to them from breaking
> everything.
> If we ignore some calls to kasan_disable_current() to prevent
> overflows, the pairing calls to kasan_enable_current() will bring
> |current->kasan_depth| to an invalid state.
> 
> E.g. if I'm understanding your idea correctly, after the following
> sequence of calls:
>   kasan_disable_current();  // #1
>   kasan_disable_current();  // #2
>   kasan_enable_current();  // #3
>   kasan_enable_current();  // #4
> 
> the value of |current->kasan_depth| will be 2, so a single subsequent
> call to kasan_disable_current() won't disable KASAN.
> 
> I think we'd better add BUG checks to bail out if the value of
> |current->kasan_depth| is too big or too small.
> 

For me, BUG_ON is OK. e.g.

 - BUG_ON(!kasan_depth) as soon as be in kasan_enable_current().

 - BUG_ON(!(kasan_depth - 1)) as soon as be in kasan_disable_current().

Welcome another members ideas, if no any additional reply within 3 days,
I shall send patch v2 for it.


Thanks.
-- 
Chen Gang (陈刚)

Managing Natural Environments is the Duty of Human Beings.