Re: [PATCH bpf v2 1/2] bpf: Keep refcount_acquire nullable for borrowed RCU kptrs

[Greg KH <greg@kroah.com>]

On Sun, Jul 26, 2026 at 04:50:29PM -0700, Ning Ding wrote:
> bpf_refcount_acquire() returns NULL if the object's refcount has
> reached zero.  For an RCU-loaded map kptr, another thread can replace
> the map entry and drop the last owning reference before the acquire,
> which makes the ref count drop to 0.
> 
> However, the verifier incorrectly marks the input as owning solely because it
> lacks NON_OWN_REF, and therefore treats the return value as non-NULL.
> This allows an unchecked NULL return to be passed to bpf_obj_drop(),
> which can crash the kernel.
> 
> Only treat the input as owning when it is present in the verifier's
> acquired-reference state. Add tests for owning input, checked borrowed
> RCU input, and unchecked borrowed RCU input.
> 
> Fixes: 7793fc3babe9 ("bpf: Make bpf_refcount_acquire fallible for non-owning refs")
> Assisted-by: Codex:gpt-5.5
> Assisted-by: ChatGPT:GPT-5.6-Thinking
> Signed-off-by: Ning Ding <dingning04@gmail.com>
> ---
>  kernel/bpf/verifier.c                         |  2 +-
>  .../selftests/bpf/progs/refcounted_kptr.c     | 61 +++++++++++++++++++
>  .../bpf/progs/refcounted_kptr_fail.c          | 47 ++++++++++++++
>  3 files changed, 109 insertions(+), 1 deletion(-)
> 

Hi,

This is the friendly patch-bot of Greg Kroah-Hartman.  You have sent him
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