linux-kernel - Re: [PATCH] powerpc/mm: Fix null-pointer dereference in pgtable_cache

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Message-ID: <9d871364-7baa-4daf-8b0c-3fbfbede6fdb@kylinos.cn>
Date:   Mon, 27 Nov 2023 14:04:24 +0800
From:   Kunwu Chan <chentao@...inos.cn>
To:     Christophe Leroy <christophe.leroy@...roup.eu>,
        "mpe@...erman.id.au" <mpe@...erman.id.au>,
        "npiggin@...il.com" <npiggin@...il.com>
Cc:     "kunwu.chan@...mail.com" <kunwu.chan@...mail.com>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] powerpc/mm: Fix null-pointer dereference in
 pgtable_cache_add

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@...inos.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@...inos.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
>>