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@xxxxxxxxxx> 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@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