Re: [PATCH v2] powerpc/mm: Fix null-pointer dereference in pgtable_cache_add

[Kunwu Chan]

Sure,i'll follow your suggestion in v3 patch:
1. set new to NULL
2. add a 'if' judgment before 'kmem_cache_create'

Thanks,
Kunwu

On 2023/12/1 18:17, Michael Ellerman wrote:

avoid two calls to panic

Re: [PATCH v2] powerpc/mm: Fix null-pointer dereference in pgtable_cache_add

[Michael Ellerman]

Kunwu Chan  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 
> Suggested-by: Michael Ellerman 
> Signed-off-by: Kunwu Chan 
> ---
> 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

[PATCH v2] 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.

Suggested-by: Christophe Leroy 
Suggested-by: Michael Ellerman 
Signed-off-by: Kunwu Chan 
---
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);
-- 
2.34.1