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@xxxxxxxxxx. 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@xxxxxxxxxx>
> > ---
> >    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