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

From: Kunwu Chan
Date: Thu Nov 30 2023 - 03:45:53 EST


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