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Date:   Wed, 3 Nov 2021 23:30:34 -0700
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Subject: Re: [PATCH bpf-next v5 1/2] bpf: support BPF_PROG_QUERY for progs
 attached to sockmap
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To:     "zhudi (E)" <zhudi2@huawei.com>,
        "davem@davemloft.net" <davem@davemloft.net>,
        "ast@kernel.org" <ast@kernel.org>,
        "daniel@iogearbox.net" <daniel@iogearbox.net>,
        "andrii@kernel.org" <andrii@kernel.org>,
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        "songliubraving@fb.com" <songliubraving@fb.com>,
        "john.fastabend@gmail.com" <john.fastabend@gmail.com>,
        "kpsingh@kernel.org" <kpsingh@kernel.org>,
        "jakub@cloudflare.com" <jakub@cloudflare.com>
CC:     "bpf@vger.kernel.org" <bpf@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
References: <a65e2f2b9aa441518000b4741bc29a90@huawei.com>
From:   Yonghong Song <yhs@fb.com>
In-Reply-To: <a65e2f2b9aa441518000b4741bc29a90@huawei.com>
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On 11/3/21 11:07 PM, zhudi (E) wrote:
>   > On 11/3/21 6:07 PM, Di Zhu wrote:
>>> Right now there is no way to query whether BPF programs are
>>> attached to a sockmap or not.
>>>
>>> we can use the standard interface in libbpf to query, such as:
>>> bpf_prog_query(mapFd, BPF_SK_SKB_STREAM_PARSER, 0, NULL, ...);
>>> the mapFd is the fd of sockmap.
>>>
>>> Signed-off-by: Di Zhu <zhudi2@huawei.com>
>>> ---
>>> /* v2 */
>>> - John Fastabend <john.fastabend@gmail.com>
>>>     - add selftest code
>>>
>>> /* v3 */
>>>    - avoid sleeping caused by copy_to_user() in rcu critical zone
>>>
>>> /* v4 */
>>>    - Alexei Starovoitov <alexei.starovoitov@gmail.com>
>>>     -split into two patches, one for core code and one for selftest.
>>>
>>> /* v5 */
>>>    - Yonghong Song <yhs@fb.com>
>>>     -Some naming and formatting changes
>>> ---
>>>    include/linux/bpf.h  |  9 ++++++
>>>    kernel/bpf/syscall.c |  5 +++
>>>    net/core/sock_map.c  | 74
>> +++++++++++++++++++++++++++++++++++++++-----
>>>    3 files changed, 81 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
>>> index d604c8251d88..235ea7fc5fd8 100644
>>> --- a/include/linux/bpf.h
>>> +++ b/include/linux/bpf.h
>>> @@ -1961,6 +1961,9 @@ int bpf_prog_test_run_syscall(struct bpf_prog
>> *prog,
>>>    int sock_map_get_from_fd(const union bpf_attr *attr, struct bpf_prog
>> *prog);
>>>    int sock_map_prog_detach(const union bpf_attr *attr, enum bpf_prog_type
>> ptype);
>>>    int sock_map_update_elem_sys(struct bpf_map *map, void *key, void
>> *value, u64 flags);
>>> +int sock_map_bpf_prog_query(const union bpf_attr *attr,
>>> +			    union bpf_attr __user *uattr);
>>> +
>>>    void sock_map_unhash(struct sock *sk);
>>>    void sock_map_close(struct sock *sk, long timeout);
>>>    #else
>>> @@ -2014,6 +2017,12 @@ static inline int sock_map_update_elem_sys(struct
>> bpf_map *map, void *key, void
>>>    {
>>>    	return -EOPNOTSUPP;
>>>    }
>>> +
>>> +static inline int sock_map_bpf_prog_query(const union bpf_attr *attr,
>>> +					  union bpf_attr __user *uattr)
>>> +{
>>> +	return -EINVAL;
>>> +}
>>>    #endif /* CONFIG_BPF_SYSCALL */
>>>    #endif /* CONFIG_NET && CONFIG_BPF_SYSCALL */
>>>
>>> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
>>> index 4e50c0bfdb7d..748102c3e0c9 100644
>>> --- a/kernel/bpf/syscall.c
>>> +++ b/kernel/bpf/syscall.c
>>> @@ -3275,6 +3275,11 @@ static int bpf_prog_query(const union bpf_attr
>> *attr,
>>>    	case BPF_FLOW_DISSECTOR:
>>>    	case BPF_SK_LOOKUP:
>>>    		return netns_bpf_prog_query(attr, uattr);
>>> +	case BPF_SK_SKB_STREAM_PARSER:
>>> +	case BPF_SK_SKB_STREAM_VERDICT:
>>> +	case BPF_SK_MSG_VERDICT:
>>> +	case BPF_SK_SKB_VERDICT:
>>> +		return sock_map_bpf_prog_query(attr, uattr);
>>>    	default:
>>>    		return -EINVAL;
>>>    	}
>>> diff --git a/net/core/sock_map.c b/net/core/sock_map.c
>>> index e252b8ec2b85..0320d27550fe 100644
>>> --- a/net/core/sock_map.c
>>> +++ b/net/core/sock_map.c
>>> @@ -1412,38 +1412,50 @@ static struct sk_psock_progs
>> *sock_map_progs(struct bpf_map *map)
>>>    	return NULL;
>>>    }
>>>
>>> -static int sock_map_prog_update(struct bpf_map *map, struct bpf_prog
>> *prog,
>>> -				struct bpf_prog *old, u32 which)
>>> +static int sock_map_prog_lookup(struct bpf_map *map, struct bpf_prog
>> ***pprog,
>>> +				u32 which)
>>>    {
>>>    	struct sk_psock_progs *progs = sock_map_progs(map);
>>> -	struct bpf_prog **pprog;
>>>
>>>    	if (!progs)
>>>    		return -EOPNOTSUPP;
>>>
>>>    	switch (which) {
>>>    	case BPF_SK_MSG_VERDICT:
>>> -		pprog = &progs->msg_parser;
>>> +		*pprog = &progs->msg_parser;
>>>    		break;
>>>    #if IS_ENABLED(CONFIG_BPF_STREAM_PARSER)
>>>    	case BPF_SK_SKB_STREAM_PARSER:
>>> -		pprog = &progs->stream_parser;
>>> +		*pprog = &progs->stream_parser;
>>>    		break;
>>>    #endif
>>>    	case BPF_SK_SKB_STREAM_VERDICT:
>>>    		if (progs->skb_verdict)
>>>    			return -EBUSY;
>>> -		pprog = &progs->stream_verdict;
>>> +		*pprog = &progs->stream_verdict;
>>>    		break;
>>>    	case BPF_SK_SKB_VERDICT:
>>>    		if (progs->stream_verdict)
>>>    			return -EBUSY;
>>> -		pprog = &progs->skb_verdict;
>>> +		*pprog = &progs->skb_verdict;
>>>    		break;
>>>    	default:
>>>    		return -EOPNOTSUPP;
>>>    	}
>>>
>>> +	return 0;
>>> +}
>>> +
>>> +static int sock_map_prog_update(struct bpf_map *map, struct bpf_prog
>> *prog,
>>> +				struct bpf_prog *old, u32 which)
>>> +{
>>> +	struct bpf_prog **pprog;
>>> +	int ret;
>>> +
>>> +	ret = sock_map_prog_lookup(map, &pprog, which);
>>> +	if (ret)
>>> +		return ret;
>>> +
>>>    	if (old)
>>>    		return psock_replace_prog(pprog, prog, old);
>>>
>>> @@ -1451,6 +1463,54 @@ static int sock_map_prog_update(struct bpf_map
>> *map, struct bpf_prog *prog,
>>>    	return 0;
>>>    }
>>>
>>> +int sock_map_bpf_prog_query(const union bpf_attr *attr,
>>> +			    union bpf_attr __user *uattr)
>>> +{
>>> +	__u32 __user *prog_ids = u64_to_user_ptr(attr->query.prog_ids);
>>> +	u32 prog_cnt = 0, flags = 0, ufd = attr->target_fd;
>>> +	struct bpf_prog **pprog;
>>> +	struct bpf_prog *prog;
>>> +	struct bpf_map *map;
>>> +	struct fd f;
>>> +	u32 id = 0;
>>
>> There is no need to initialize 'id = 0'. id will be assigned later.
> 
> 
> if (!attr->query.prog_cnt || !prog_ids || !prog_cnt) is met, the id will not be assigned later.
> At the end of the function, we judge whether to copy the program ID by the value of the id.

Ya, that is true. id = 0 is indeed needed.

> 
> 
>>
>>> +	int ret;
>>> +
>>> +	if (attr->query.query_flags)
>>> +		return -EINVAL;
>>> +
>>> +	f = fdget(ufd);
>>> +	map = __bpf_map_get(f);
>>> +	if (IS_ERR(map))
>>> +		return PTR_ERR(map);
>>> +
>>> +	rcu_read_lock();
>>> +
>>> +	ret = sock_map_prog_lookup(map, &pprog, attr->query.attach_type);
>>> +	if (ret)
>>> +		goto end;
>>> +
>>> +	prog = *pprog;
>>> +	prog_cnt = (!prog) ? 0 : 1;
>>
>> (!prog) => !prog ?
> 
> Yes, It's just my habit
> 
>>
>>> +
>>> +	if (!attr->query.prog_cnt || !prog_ids || !prog_cnt)
>>> +		goto end;
>>> +
>>> +	id = prog->aux->id;
>>> +	if (id == 0)
>>> +		prog_cnt = 0;
>>
>>
>> id will never be 0, see function bpf_prog_alloc_id() is syscall.c.
>> So 'if (id == 0)' check is not needed.
> 
> 
> Because we do not hold the reference count, the program may be released synchronously

   synchronously => asynchronously

> and its ID will be set to 0 in bpf_prog_free_id().
> 
> Is that right?

Just checked the code again. You are right. Maybe add a comment here to
make it clear why we check id == 0 here?

> 
> 
>>
>>> +
>>> +end:
>>> +	rcu_read_unlock();
>>> +
>>> +	if (copy_to_user(&uattr->query.attach_flags, &flags, sizeof(flags)) ||
>>> +	    (id != 0 && copy_to_user(prog_ids, &id, sizeof(u32))) ||
>>> +	    copy_to_user(&uattr->query.prog_cnt, &prog_cnt, sizeof(prog_cnt)))
>>> +		ret = -EFAULT;
>>> +
>>> +	fdput(f);
>>> +	return ret;
>>> +}
>>> +
>>>    static void sock_map_unlink(struct sock *sk, struct sk_psock_link *link)
>>>    {
>>>    	switch (link->map->map_type) {
>>>