Re: [PATCH bpf-next v7 6/6] selftests/bpf: tc_tunnel - validate decap GSO and encapsulation state

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Invalid pointer arithmetic `kskb->head + kskb->end` breaks 32-bit compilation and cross-architecture CO-RE portability.
--

--- Patch [6]: [PATCH bpf-next v7 6/6] selftests/bpf: tc_tunnel - validate decap GSO and encapsulation state ---
commit 51cad3ba4cd10bce6b9c9134b5e4188fc76f034c
Author: Nick Hudson <nhudson@akamai.com>
selftests/bpf: tc_tunnel - validate decap GSO and encapsulation state

This commit tightens tc_tunnel tests by verifying post-decap tunnel
state for both GSO and non-GSO packets. It enforces DECAP flags and
ensures proper clearing of gso_type bits and encapsulation state.

> diff --git a/tools/testing/selftests/bpf/progs/test_tc_tunnel.c b/tools/testing/selftests/bpf/progs/test_tc_tunnel.c
> --- a/tools/testing/selftests/bpf/progs/test_tc_tunnel.c
> +++ b/tools/testing/selftests/bpf/progs/test_tc_tunnel.c

[ ... ]

> @@ -655,6 +688,40 @@ static int decap_internal(struct __sk_buff *skb, int off, int len, char proto)
>  	if (bpf_skb_adjust_room(skb, -olen, BPF_ADJ_ROOM_MAC, flags))
>  		return TC_ACT_SHOT;
>  
> +	kskb = bpf_cast_to_kern_ctx(skb);
> +	shinfo = bpf_core_cast(kskb->head + kskb->end, struct skb_shared_info);
                                       ^^^^^^^^^^^^^^^^^^^^^

[Severity: Medium]
Does this pointer arithmetic break compilation on 32-bit architectures?

Since kskb->end is a pointer on 32-bit systems (rather than an integer offset
like it is on 64-bit), adding kskb->head and kskb->end together attempts to add
two pointers, which is invalid in C.

Additionally, CO-RE does not translate this pointer-integer addition to a single
pointer dereference when cross-compiled on 64-bit and run on 32-bit kernels,
which can lead to a garbage pointer dereference.

Is there a safer way to calculate the skb_shared_info offset in decap_internal
that is portable across both 32-bit and 64-bit architectures?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260812083115.73100-1-nhudson@akamai.com?part=6