linux-kernel - Re: [PATCH v2] powerpc/mm: Fix null-pointer dereference in pgtable_cache

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Date:   Fri, 01 Dec 2023 21:17:28 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Kunwu Chan <chentao@...inos.cn>, npiggin@...il.com,
        christophe.leroy@...roup.eu
Cc:     kunwu.chan@...mail.com, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, Kunwu Chan <chentao@...inos.cn>
Subject: Re: [PATCH v2] powerpc/mm: Fix null-pointer dereference in
 pgtable_cache_add

Kunwu Chan <chentao@...inos.cn> writes:
> kasprintf() returns a pointer to dynamically allocated memory
> which can be NULL upon failure. Ensure the allocation was successful
> by checking the pointer validity.
>
> Suggested-by: Christophe Leroy <christophe.leroy@...roup.eu>
> Suggested-by: Michael Ellerman <mpe@...erman.id.au>
> Signed-off-by: Kunwu Chan <chentao@...inos.cn>
> ---
> v2: Use "panic" instead of "return"
> ---
>  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..9788950b33f5 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)
> +		panic("Failed to allocate memory for order %d", shift);
>  	new = kmem_cache_create(name, table_size, align, 0, ctor(shift));
>  	if (!new)
>  		panic("Could not allocate pgtable cache for order %d", shift);

It would be nice to avoid two calls to panic. Can you reorganise the
logic so that there's only one? Initialising new to NULL might help.

cheers