[PATCH] powerpc/mm: Fix null-pointer dereference in pgtable_cache_add

[PATCH] powerpc/mm: Fix null-pointer dereference in pgtable_cache_add

[Kunwu Chan]

kasprintf() returns a pointer to dynamically allocated memory
which can be NULL upon failure. Ensure the allocation was successful
by checking the pointer validity.

Signed-off-by: Kunwu Chan <chentao@kylinos.cn>
---
 arch/powerpc/mm/init-common.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/powerpc/mm/init-common.c b/arch/powerpc/mm/init-common.c
index 119ef491f797..0884fc601c46 100644
--- a/arch/powerpc/mm/init-common.c
+++ b/arch/powerpc/mm/init-common.c
@@ -139,6 +139,8 @@ void pgtable_cache_add(unsigned int shift)
 
 	align = max_t(unsigned long, align, minalign);
 	name = kasprintf(GFP_KERNEL, "pgtable-2^%d", shift);
+	if (!name)
+		return;
 	new = kmem_cache_create(name, table_size, align, 0, ctor(shift));
 	if (!new)
 		panic("Could not allocate pgtable cache for order %d", shift);
-- 
2.34.1

Re: [PATCH] powerpc/mm: Fix null-pointer dereference in pgtable_cache_add

[Christophe Leroy]

Le 22/11/2023 à 10:00, Kunwu Chan a écrit :
> [Vous ne recevez pas souvent de courriers de chentao@kylinos.cn. Découvrez pourquoi ceci est important à https://aka.ms/LearnAboutSenderIdentification ]
> 
> kasprintf() returns a pointer to dynamically allocated memory
> which can be NULL upon failure. Ensure the allocation was successful
> by checking the pointer validity.

Are you sure this is needed ? Did you check what happens what name is NULL ?

If I followed stuff correctly, I end up in function 
sysfs_do_create_link_sd() which already handles the NULL name case which 
a big hammer warning.

> 
> Signed-off-by: Kunwu Chan <chentao@kylinos.cn>
> ---
>   arch/powerpc/mm/init-common.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/arch/powerpc/mm/init-common.c b/arch/powerpc/mm/init-common.c
> index 119ef491f797..0884fc601c46 100644
> --- a/arch/powerpc/mm/init-common.c
> +++ b/arch/powerpc/mm/init-common.c
> @@ -139,6 +139,8 @@ void pgtable_cache_add(unsigned int shift)
> 
>          align = max_t(unsigned long, align, minalign);
>          name = kasprintf(GFP_KERNEL, "pgtable-2^%d", shift);
> +       if (!name)
> +               return;
>          new = kmem_cache_create(name, table_size, align, 0, ctor(shift));
>          if (!new)
>                  panic("Could not allocate pgtable cache for order %d", shift);
> --
> 2.34.1
> 

Re: [PATCH] powerpc/mm: Fix null-pointer dereference in pgtable_cache_add

[Kunwu Chan]

Hi Christophe,

Thanks for your reply.
It's my bad. According your reply, i read the code in 
sysfs_do_create_link_sd.There is a null pointer check indeed.

My intention was to check null pointer after memory allocation.
Whether we can add a comment here for someone like me, the null pointer 
check is no need here?

Thanks,
Kunwu

On 2023/11/24 23:17, Christophe Leroy wrote:
> 
> 
> Le 22/11/2023 à 10:00, Kunwu Chan a écrit :
>> [Vous ne recevez pas souvent de courriers de chentao@kylinos.cn. Découvrez pourquoi ceci est important à https://aka.ms/LearnAboutSenderIdentification ]
>>
>> kasprintf() returns a pointer to dynamically allocated memory
>> which can be NULL upon failure. Ensure the allocation was successful
>> by checking the pointer validity.
> 
> Are you sure this is needed ? Did you check what happens what name is NULL ?
> 
> If I followed stuff correctly, I end up in function
> sysfs_do_create_link_sd() which already handles the NULL name case which
> a big hammer warning.
> 
>>
>> Signed-off-by: Kunwu Chan <chentao@kylinos.cn>
>> ---
>>    arch/powerpc/mm/init-common.c | 2 ++
>>    1 file changed, 2 insertions(+)
>>
>> diff --git a/arch/powerpc/mm/init-common.c b/arch/powerpc/mm/init-common.c
>> index 119ef491f797..0884fc601c46 100644
>> --- a/arch/powerpc/mm/init-common.c
>> +++ b/arch/powerpc/mm/init-common.c
>> @@ -139,6 +139,8 @@ void pgtable_cache_add(unsigned int shift)
>>
>>           align = max_t(unsigned long, align, minalign);
>>           name = kasprintf(GFP_KERNEL, "pgtable-2^%d", shift);
>> +       if (!name)
>> +               return;
>>           new = kmem_cache_create(name, table_size, align, 0, ctor(shift));
>>           if (!new)
>>                   panic("Could not allocate pgtable cache for order %d", shift);
>> --
>> 2.34.1
>>

Re: [PATCH] powerpc/mm: Fix null-pointer dereference in pgtable_cache_add

[Michael Ellerman]

Kunwu Chan <chentao@kylinos.cn> writes:
> Hi Christophe,
>
> Thanks for your reply.
> It's my bad. According your reply, i read the code in 
> sysfs_do_create_link_sd.There is a null pointer check indeed.
>
> My intention was to check null pointer after memory allocation.
> Whether we can add a comment here for someone like me, the null pointer 
> check is no need here?

I don't mind there being a NULL check for name.

But the code shouldn't silently return if name can't be allocated.
Notice that if we can't create the cache we *panic*. A failure to
allocate name, which causes us to skip the cache creation, needs to also
panic.

cheers

> On 2023/11/24 23:17, Christophe Leroy wrote:
>> 
>> 
>> Le 22/11/2023 à 10:00, Kunwu Chan a écrit :
>>> [Vous ne recevez pas souvent de courriers de chentao@kylinos.cn. Découvrez pourquoi ceci est important à https://aka.ms/LearnAboutSenderIdentification ]
>>>
>>> kasprintf() returns a pointer to dynamically allocated memory
>>> which can be NULL upon failure. Ensure the allocation was successful
>>> by checking the pointer validity.
>> 
>> Are you sure this is needed ? Did you check what happens what name is NULL ?
>> 
>> If I followed stuff correctly, I end up in function
>> sysfs_do_create_link_sd() which already handles the NULL name case which
>> a big hammer warning.
>> 
>>>
>>> Signed-off-by: Kunwu Chan <chentao@kylinos.cn>
>>> ---
>>>    arch/powerpc/mm/init-common.c | 2 ++
>>>    1 file changed, 2 insertions(+)
>>>
>>> diff --git a/arch/powerpc/mm/init-common.c b/arch/powerpc/mm/init-common.c
>>> index 119ef491f797..0884fc601c46 100644
>>> --- a/arch/powerpc/mm/init-common.c
>>> +++ b/arch/powerpc/mm/init-common.c
>>> @@ -139,6 +139,8 @@ void pgtable_cache_add(unsigned int shift)
>>>
>>>           align = max_t(unsigned long, align, minalign);
>>>           name = kasprintf(GFP_KERNEL, "pgtable-2^%d", shift);
>>> +       if (!name)
>>> +               return;
>>>           new = kmem_cache_create(name, table_size, align, 0, ctor(shift));
>>>           if (!new)
>>>                   panic("Could not allocate pgtable cache for order %d", shift);
>>> --
>>> 2.34.1
>>>

Re: [PATCH] powerpc/mm: Fix null-pointer dereference in pgtable_cache_add

[Kunwu Chan]

Thanks for your reply.

Ok, I know what you mean, when name is NULL. The process should be 
aborted and the specific reason for the error should be printed, not 
just return.

I will update v2 patch with "panic".

Thanks again,
Kunwu

On 2023/11/28 19:32, Michael Ellerman wrote:
> Kunwu Chan <chentao@kylinos.cn> writes:
>> Hi Christophe,
>>
>> Thanks for your reply.
>> It's my bad. According your reply, i read the code in
>> sysfs_do_create_link_sd.There is a null pointer check indeed.
>>
>> My intention was to check null pointer after memory allocation.
>> Whether we can add a comment here for someone like me, the null pointer
>> check is no need here?
> 
> I don't mind there being a NULL check for name.
> 
> But the code shouldn't silently return if name can't be allocated.
> Notice that if we can't create the cache we *panic*. A failure to
> allocate name, which causes us to skip the cache creation, needs to also
> panic.
> 
> cheers
> 
>> On 2023/11/24 23:17, Christophe Leroy wrote:
>>>
>>>
>>> Le 22/11/2023 à 10:00, Kunwu Chan a écrit :
>>>> [Vous ne recevez pas souvent de courriers de chentao@kylinos.cn. Découvrez pourquoi ceci est important à https://aka.ms/LearnAboutSenderIdentification ]
>>>>
>>>> kasprintf() returns a pointer to dynamically allocated memory
>>>> which can be NULL upon failure. Ensure the allocation was successful
>>>> by checking the pointer validity.
>>>
>>> Are you sure this is needed ? Did you check what happens what name is NULL ?
>>>
>>> If I followed stuff correctly, I end up in function
>>> sysfs_do_create_link_sd() which already handles the NULL name case which
>>> a big hammer warning.
>>>
>>>>
>>>> Signed-off-by: Kunwu Chan <chentao@kylinos.cn>
>>>> ---
>>>>     arch/powerpc/mm/init-common.c | 2 ++
>>>>     1 file changed, 2 insertions(+)
>>>>
>>>> diff --git a/arch/powerpc/mm/init-common.c b/arch/powerpc/mm/init-common.c
>>>> index 119ef491f797..0884fc601c46 100644
>>>> --- a/arch/powerpc/mm/init-common.c
>>>> +++ b/arch/powerpc/mm/init-common.c
>>>> @@ -139,6 +139,8 @@ void pgtable_cache_add(unsigned int shift)
>>>>
>>>>            align = max_t(unsigned long, align, minalign);
>>>>            name = kasprintf(GFP_KERNEL, "pgtable-2^%d", shift);
>>>> +       if (!name)
>>>> +               return;
>>>>            new = kmem_cache_create(name, table_size, align, 0, ctor(shift));
>>>>            if (!new)
>>>>                    panic("Could not allocate pgtable cache for order %d", shift);
>>>> --
>>>> 2.34.1
>>>>