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Date:   Wed, 17 Oct 2018 23:25:58 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Song Liu <songliubraving@...com>
Cc:     netdev@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
        kernel-team@...com
Subject: Re: [PATCH v3 bpf-next 2/2] bpf: add tests for direct packet access
 from CGROUP_SKB

On Wed, Oct 17, 2018 at 10:39:49PM -0700, 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@...com>
> ---
>  net/bpf/test_run.c                          |   4 +
>  tools/testing/selftests/bpf/test_verifier.c | 170 ++++++++++++++++++++
>  2 files changed, 174 insertions(+)
> 
> diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
> index 0c423b8cd75c..c7210e2f1ae9 100644
> --- a/net/bpf/test_run.c
> +++ b/net/bpf/test_run.c
> @@ -10,6 +10,7 @@
>  #include <linux/etherdevice.h>
>  #include <linux/filter.h>
>  #include <linux/sched/signal.h>
> +#include <net/sock.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 +116,7 @@ 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;
>  	void *data;
>  	int ret;
>  
> @@ -142,6 +144,8 @@ int bpf_prog_test_run_skb(struct bpf_prog *prog, const union bpf_attr *kattr,
>  		kfree(data);
>  		return -ENOMEM;
>  	}
> +	sock_init_data(NULL, &sk);
> +	skb->sk = &sk;

I was about to apply it, but it crashes as:
[   16.830822] BUG: unable to handle kernel paging request at 000000014427b974
[   16.831363] PGD 8000000135ecf067 P4D 8000000135ecf067 PUD 0
[   16.831792] Oops: 0000 [#1] SMP PTI
[   16.832061] CPU: 1 PID: 1965 Comm: test_verifier Not tainted 4.19.0-rc7-02550-ga76dee97ff12 #1153
[   16.832712] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.0-2.el7 04/01/2014
[   16.833358] RIP: 0010:cmp_map_id+0x10/0x50
[   16.835036] RSP: 0018:ffffc9000080faf8 EFLAGS: 00010246
[   16.835429] RAX: 00000000ffffffff RBX: 0000000036069ee8 RCX: 0000000000000000
[   16.835958] RDX: 000000014427b970 RSI: 000000014427b970 RDI: ffffc9000080fb44
[   16.836496] RBP: 000000000000000c R08: ffffffff810f7330 R09: 0000000036069ee8
[   16.837026] R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000000
[   16.837554] R13: ffffffff810f7330 R14: 000000014427b970 R15: 000000001b034f74
[   16.838083] FS:  00007fae50663700(0000) GS:ffff88013ba80000(0000) knlGS:0000000000000000
[   16.838677] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   16.839105] CR2: 000000014427b974 CR3: 0000000135934005 CR4: 00000000003606e0
[   16.839632] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   16.840157] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   16.840682] Call Trace:
[   16.840897]  bsearch+0x50/0x90
[   16.841144]  map_id_range_down+0x81/0xa0
[   16.841438]  make_kuid+0xf/0x10
[   16.841677]  sock_init_data+0x24f/0x260
[   16.841979]  bpf_prog_test_run_skb+0x9e/0x270

I suspect sock_net_set(sk, &init_net) is necessary before sock_init_data() call.

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