Re: [PATCH bpf 1/2] bpf: Mark bpf_get_kmem_cache() as nullable

["Alexei Starovoitov" <alexei.starovoitov@gmail.com>]

On Sat Jun 20, 2026 at 8:47 AM PDT, Nuoqi Gui wrote:
> bpf_get_kmem_cache() returns NULL when virt_addr_valid() rejects the
> address or when virt_to_slab() does not find a slab. The verifier uses
> KF_RET_NULL to add PTR_MAYBE_NULL to kfunc return registers, but the
> registration currently lacks that flag.
>
> Add KF_RET_NULL so callers have to prove that the returned kmem_cache
> pointer is non-NULL before dereferencing fields.
>
> Fixes: a992d7a397912 ("mm/bpf: Add bpf_get_kmem_cache() kfunc")
> Signed-off-by: Nuoqi Gui <gnq25@mails.tsinghua.edu.cn>
> ---
>  kernel/bpf/helpers.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index b5314c9fed3cf..57a6ab72ae3cc 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -4817,7 +4817,7 @@ BTF_ID_FLAGS(func, bpf_iter_bits_next, KF_ITER_NEXT | KF_RET_NULL)
>  BTF_ID_FLAGS(func, bpf_iter_bits_destroy, KF_ITER_DESTROY)
>  BTF_ID_FLAGS(func, bpf_copy_from_user_str, KF_SLEEPABLE)
>  BTF_ID_FLAGS(func, bpf_copy_from_user_task_str, KF_SLEEPABLE)
> -BTF_ID_FLAGS(func, bpf_get_kmem_cache)
> +BTF_ID_FLAGS(func, bpf_get_kmem_cache, KF_RET_NULL)

This is wrong. Nothing to fix.
It works as designed.
Instead of sending broken patches do your home work.
You're saying commit a992d7a397912 is buggy. Read its commit log, selftest
and the email thread and see why this patch is wrong.

Such poor quality patches undermine your other legitimate fixes.
You have to step up in quality.

pw-bot: cr