Re: [PATCH bpf-next v4 1/2] bpf: support BPF_PROG_QUERY for progs attached to sockmap

[Yonghong Song <yhs@fb.com>]

On 11/2/21 1:48 AM, 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>
> ---
>   include/linux/bpf.h  |  9 +++++
>   kernel/bpf/syscall.c |  5 +++
>   net/core/sock_map.c  | 88 ++++++++++++++++++++++++++++++++++++++++----
>   3 files changed, 95 insertions(+), 7 deletions(-)
> 
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index d604c8251d88..594ca91992db 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 sockmap_bpf_prog_query(const union bpf_attr *attr,
> +			   union bpf_attr __user *uattr);

All previous functions are with prefix "sock_map". Why you choose
a different prefix "sockmap"?

> +
>   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 sockmap_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..17faeff8f85f 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 sockmap_bpf_prog_query(attr, uattr);
>   	default:
>   		return -EINVAL;
>   	}
> diff --git a/net/core/sock_map.c b/net/core/sock_map.c
> index e252b8ec2b85..ca65ed0004d3 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[],

Can we just change "**pprog[]" to "***pprog"? In the code, you really 
just pass the address of the decl "struct bpf_prog **pprog;" to the 
function.

> +				u32 which)

Some format issue here?

>   {
>   	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)

Some format issue here?

> +{
> +	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 +1463,68 @@ static int sock_map_prog_update(struct bpf_map *map, struct bpf_prog *prog,
>   	return 0;
>   }
>   
> +int sockmap_bpf_prog_query(const union bpf_attr *attr,
> +			   union bpf_attr __user *uattr)

Format issue here?

> +{
> +	__u32 __user *prog_ids = u64_to_user_ptr(attr->query.prog_ids);

Typically we use u32 in the kernel code. But I know there are __u32 
usage as well, esp. with __user attributes. I put a comment here just
in case that somebody else has a different opinion.

> +	u32 prog_cnt = 0, flags = 0;
> +	u32 ufd = attr->target_fd;

You can merge the above u32 together.

> +	struct bpf_prog **pprog;
> +	struct bpf_prog *prog;
> +	struct bpf_map *map;
> +	struct fd f;
> +	int ret;
> +	u32 id = 0;

to maintain reverse christmas tree?

> +
> +	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;
> +
> +	if (!attr->query.prog_cnt || !prog_ids || !prog_cnt)
> +		goto end;
> +
> +	prog = bpf_prog_inc_not_zero(prog);

Could you explain why we need bpf_prog_inc_not_zero here?
We are inside rcu_read_lock/unlock region. We got a program
from *pprog. If this program is not NULL, this program should
not disappear since we are in rcu read lock region, right?
Maybe I missed something, it would be good you can explain
the scenario you try to pretect here.

> +	if (IS_ERR(prog)) {
> +		ret = PTR_ERR(prog);
> +		goto end;
> +	}
> +	id = prog->aux->id;
> +	bpf_prog_put(prog);
> +
> +end:
> +	rcu_read_unlock();
> +
> +	if (copy_to_user(&uattr->query.attach_flags, &flags, sizeof(flags))) {
> +		ret = -EFAULT;
> +		goto err;
> +	}
> +	if (id != 0 && copy_to_user(prog_ids, &id, sizeof(u32))) {
> +		ret = -EFAULT;
> +		goto err;
> +	}
> +	if (copy_to_user(&uattr->query.prog_cnt, &prog_cnt, sizeof(prog_cnt))) {
> +		ret = -EFAULT;
> +		goto err;
> +	}

You can do

	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;

to make code a little bit concise.

> +
> +err:
> +	fdput(f);
> +	return ret;
> +}
> +
>   static void sock_map_unlink(struct sock *sk, struct sk_psock_link *link)
>   {
>   	switch (link->map->map_type) {
>