netdev - Re: [PATCH bpf-next v4 02/21] bpf: allow loading of a bpf

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Message-ID: <c128a30f-af40-99c9-706e-4afe268ed38f@fb.com>
Date:   Tue, 12 May 2020 08:41:19 -0700
From:   Yonghong Song <yhs@...com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
CC:     Andrii Nakryiko <andriin@...com>, <bpf@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>, <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>, <kernel-team@...com>
Subject: Re: [PATCH bpf-next v4 02/21] bpf: allow loading of a bpf_iter
 program



On 5/9/20 5:41 PM, Alexei Starovoitov wrote:
> On Sat, May 09, 2020 at 10:59:00AM -0700, Yonghong Song wrote:
>> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
>> index 70ad009577f8..d725ff7d11db 100644
>> --- a/kernel/bpf/verifier.c
>> +++ b/kernel/bpf/verifier.c
>> @@ -7101,6 +7101,10 @@ static int check_return_code(struct bpf_verifier_env *env)
>>   			return 0;
>>   		range = tnum_const(0);
>>   		break;
>> +	case BPF_PROG_TYPE_TRACING:
>> +		if (env->prog->expected_attach_type != BPF_TRACE_ITER)
>> +			return 0;
>> +		break;
> 
> Not related to this set, but I just noticed that I managed to forget to
> add this check for fentry/fexit/freplace.
> While it's not too late let's enforce return 0 for them ?
> Could you follow up with a patch for bpf tree?

Just want to double check. In selftests, we have

SEC("fentry/__set_task_comm")
int BPF_PROG(prog4, struct task_struct *tsk, const char *buf, bool exec)
{
         return !tsk;
}

SEC("fexit/__set_task_comm")
int BPF_PROG(prog5, struct task_struct *tsk, const char *buf, bool exec)
{
         return !tsk;
}

fentry/fexit may returrn 1. What is the intention here? Does this mean
we should allow [0, 1] instead of [0, 0]?

For freplace, we have

__u64 test_get_skb_len = 0;
SEC("freplace/get_skb_len")
int new_get_skb_len(struct __sk_buff *skb)
{
         int len = skb->len;

         if (len != 74)
                 return 0;
         test_get_skb_len = 1;
         return 74; /* original get_skb_len() returns skb->len */
}

That means freplace may return arbitrary values depending on what
to replace?