Re: [PATCH v6 bpf-next 2/2] bpf: add tests for direct packet access from CGROUP_SKB

[Eric Dumazet <eric.dumazet@gmail.com>]

On 10/18/2018 10:53 PM, Song Liu wrote:
> Tests are added to make sure CGROUP_SKB cannot access:
>   tc_classid, data_meta, flow_keys
> 
> and can read and write:
>   mark, prority, and cb[0-4]
> 
> and can read other fields.
> 
> To make selftest with skb->sk work, a dummy sk is added in
> bpf_prog_test_run_skb().
> 
> Signed-off-by: Song Liu <songliubraving@fb.com>
> ---
>  net/bpf/test_run.c                          |   7 +
>  tools/testing/selftests/bpf/test_verifier.c | 171 ++++++++++++++++++++
>  2 files changed, 178 insertions(+)
> 
> diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
> index 0c423b8cd75c..87ea279cb095 100644
> --- a/net/bpf/test_run.c
> +++ b/net/bpf/test_run.c
> @@ -10,6 +10,8 @@
>  #include <linux/etherdevice.h>
>  #include <linux/filter.h>
>  #include <linux/sched/signal.h>
> +#include <net/sock.h>
> +#include <net/tcp.h>
>  
>  static __always_inline u32 bpf_test_run_one(struct bpf_prog *prog, void *ctx,
>  		struct bpf_cgroup_storage *storage[MAX_BPF_CGROUP_STORAGE_TYPE])
> @@ -115,6 +117,7 @@ int bpf_prog_test_run_skb(struct bpf_prog *prog, const union bpf_attr *kattr,
>  	u32 retval, duration;
>  	int hh_len = ETH_HLEN;
>  	struct sk_buff *skb;
> +	struct sock sk = {0};
>  	void *data;
>  	int ret;
>

A dummy on stack, Nah forget it.

Please compile your test kernels with common debugging features,
I am sure some horrible thing will show up.
(Like debug_object_is_on_stack())