[PATCH v5] mm/slub: avoid accessing metadata when pointer is invalid in object_err()

[PATCH v5] mm/slub: avoid accessing metadata when pointer is invalid in object_err()

[Li Qiong]

object_err() reports details of an object for further debugging, such as
the freelist pointer, redzone, etc. However, if the pointer is invalid,
attempting to access object metadata can lead to a crash since it does
not point to a valid object.

In case check_valid_pointer() returns false for the pointer, only print
the pointer value and skip accessing metadata.

Fixes: 81819f0fc828 ("SLUB core")
Cc: <stable@vger.kernel.org>
Signed-off-by: Li Qiong <liqiong@nfschina.com>
---
v2:
- rephrase the commit message, add comment for object_err().
v3:
- check object pointer in object_err().
v4:
- restore changes in alloc_consistency_checks().
v5:
- rephrase message, fix code style.
---
 mm/slub.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/mm/slub.c b/mm/slub.c
index 31e11ef256f9..b3eff1476c85 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1104,7 +1104,12 @@ static void object_err(struct kmem_cache *s, struct slab *slab,
 		return;
 
 	slab_bug(s, reason);
-	print_trailer(s, slab, object);
+	if (!check_valid_pointer(s, slab, object)) {
+		print_slab_info(slab);
+		pr_err("Invalid pointer 0x%p\n", object);
+	} else {
+		print_trailer(s, slab, object);
+	}
 	add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
 
 	WARN_ON(1);
-- 
2.30.2

Re: [PATCH v5] mm/slub: avoid accessing metadata when pointer is invalid in object_err()

[Harry Yoo]

On Mon, Aug 04, 2025 at 09:46:25AM +0800, Li Qiong wrote:
> object_err() reports details of an object for further debugging, such as
> the freelist pointer, redzone, etc. However, if the pointer is invalid,
> attempting to access object metadata can lead to a crash since it does
> not point to a valid object.
> 
> In case check_valid_pointer() returns false for the pointer, only print
> the pointer value and skip accessing metadata.
> 
> Fixes: 81819f0fc828 ("SLUB core")
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Li Qiong <liqiong@nfschina.com>
> ---
> v2:
> - rephrase the commit message, add comment for object_err().
> v3:
> - check object pointer in object_err().
> v4:
> - restore changes in alloc_consistency_checks().
> v5:
> - rephrase message, fix code style.
> ---

Looks good to me,
Reviewed-by: Harry Yoo <harry.yoo@oracle.com>

-- 
Cheers,
Harry / Hyeonggon

>  mm/slub.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index 31e11ef256f9..b3eff1476c85 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -1104,7 +1104,12 @@ static void object_err(struct kmem_cache *s, struct slab *slab,
>  		return;
>  
>  	slab_bug(s, reason);
> -	print_trailer(s, slab, object);
> +	if (!check_valid_pointer(s, slab, object)) {
> +		print_slab_info(slab);
> +		pr_err("Invalid pointer 0x%p\n", object);
> +	} else {
> +		print_trailer(s, slab, object);
> +	}
>  	add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
>  
>  	WARN_ON(1);
> -- 
> 2.30.2

Re: [PATCH v5] mm/slub: avoid accessing metadata when pointer is invalid in object_err()

[Harry Yoo]

On Mon, Aug 04, 2025 at 11:25:23AM +0900, Harry Yoo wrote:
> On Mon, Aug 04, 2025 at 09:46:25AM +0800, Li Qiong wrote:
> > object_err() reports details of an object for further debugging, such as
> > the freelist pointer, redzone, etc. However, if the pointer is invalid,
> > attempting to access object metadata can lead to a crash since it does
> > not point to a valid object.
> > 
> > In case check_valid_pointer() returns false for the pointer, only print
> > the pointer value and skip accessing metadata.
> > 
> > Fixes: 81819f0fc828 ("SLUB core")
> > Cc: <stable@vger.kernel.org>
> > Signed-off-by: Li Qiong <liqiong@nfschina.com>
> > ---
> > v2:
> > - rephrase the commit message, add comment for object_err().
> > v3:
> > - check object pointer in object_err().
> > v4:
> > - restore changes in alloc_consistency_checks().
> > v5:
> > - rephrase message, fix code style.
> > ---
> 
> Looks good to me,
> Reviewed-by: Harry Yoo <harry.yoo@oracle.com>
> 
> -- 
> Cheers,
> Harry / Hyeonggon
> 
> >  mm/slub.c | 7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> > 
> > diff --git a/mm/slub.c b/mm/slub.c
> > index 31e11ef256f9..b3eff1476c85 100644
> > --- a/mm/slub.c
> > +++ b/mm/slub.c
> > @@ -1104,7 +1104,12 @@ static void object_err(struct kmem_cache *s, struct slab *slab,
> >  		return;
> >  
> >  	slab_bug(s, reason);
> > -	print_trailer(s, slab, object);
> > +	if (!check_valid_pointer(s, slab, object)) {

Wait, hold on. check_valid_pointer() returns true when object == NULL.
the condition should be (!object || !check_valid_pointer())?

> > +		print_slab_info(slab);
> > +		pr_err("Invalid pointer 0x%p\n", object);
> > +	} else {
> > +		print_trailer(s, slab, object);
> > +	}
> >  	add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
> >  
> >  	WARN_ON(1);
> > -- 
> > 2.30.2

-- 
Cheers,
Harry / Hyeonggon

Re: [PATCH v5] mm/slub: avoid accessing metadata when pointer is invalid in object_err()

[liqiong]

在 2025/8/4 10:35, Harry Yoo 写道:
> On Mon, Aug 04, 2025 at 11:25:23AM +0900, Harry Yoo wrote:
>> On Mon, Aug 04, 2025 at 09:46:25AM +0800, Li Qiong wrote:
>>> object_err() reports details of an object for further debugging, such as
>>> the freelist pointer, redzone, etc. However, if the pointer is invalid,
>>> attempting to access object metadata can lead to a crash since it does
>>> not point to a valid object.
>>>
>>> In case check_valid_pointer() returns false for the pointer, only print
>>> the pointer value and skip accessing metadata.
>>>
>>> Fixes: 81819f0fc828 ("SLUB core")
>>> Cc: <stable@vger.kernel.org>
>>> Signed-off-by: Li Qiong <liqiong@nfschina.com>
>>> ---
>>> v2:
>>> - rephrase the commit message, add comment for object_err().
>>> v3:
>>> - check object pointer in object_err().
>>> v4:
>>> - restore changes in alloc_consistency_checks().
>>> v5:
>>> - rephrase message, fix code style.
>>> ---
>> Looks good to me,
>> Reviewed-by: Harry Yoo <harry.yoo@oracle.com>
>>
>> -- 
>> Cheers,
>> Harry / Hyeonggon
>>
>>>  mm/slub.c | 7 ++++++-
>>>  1 file changed, 6 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/mm/slub.c b/mm/slub.c
>>> index 31e11ef256f9..b3eff1476c85 100644
>>> --- a/mm/slub.c
>>> +++ b/mm/slub.c
>>> @@ -1104,7 +1104,12 @@ static void object_err(struct kmem_cache *s, struct slab *slab,
>>>  		return;
>>>  
>>>  	slab_bug(s, reason);
>>> -	print_trailer(s, slab, object);
>>> +	if (!check_valid_pointer(s, slab, object)) {
> Wait, hold on. check_valid_pointer() returns true when object == NULL.
> the condition should be (!object || !check_valid_pointer())?

You're right, i ignored this situation.


>
>>> +		print_slab_info(slab);
>>> +		pr_err("Invalid pointer 0x%p\n", object);
>>> +	} else {
>>> +		print_trailer(s, slab, object);
>>> +	}
>>>  	add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
>>>  
>>>  	WARN_ON(1);
>>> -- 
>>> 2.30.2