Re: [PATCH bpf-next v8 05/11] bpf: implement BPF_PROG_QUERY for BPF_LSM_CGROUP

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On Wed, Jun 01, 2022 at 12:02:12PM -0700, Stanislav Fomichev wrote:
> diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
> index a27a6a7bd852..cb3338ef01e0 100644
> --- a/kernel/bpf/cgroup.c
> +++ b/kernel/bpf/cgroup.c
> @@ -1035,6 +1035,7 @@ static int cgroup_bpf_detach(struct cgroup *cgrp, struct bpf_prog *prog,
>  static int __cgroup_bpf_query(struct cgroup *cgrp, const union bpf_attr *attr,
>  			      union bpf_attr __user *uattr)
>  {
> +	__u32 __user *prog_attach_flags = u64_to_user_ptr(attr->query.prog_attach_flags);
>  	__u32 __user *prog_ids = u64_to_user_ptr(attr->query.prog_ids);
>  	enum bpf_attach_type type = attr->query.attach_type;
>  	enum cgroup_bpf_attach_type atype;
> @@ -1042,50 +1043,92 @@ static int __cgroup_bpf_query(struct cgroup *cgrp, const union bpf_attr *attr,
>  	struct hlist_head *progs;
>  	struct bpf_prog *prog;
>  	int cnt, ret = 0, i;
> +	int total_cnt = 0;
>  	u32 flags;
>  
> -	atype = to_cgroup_bpf_attach_type(type);
> -	if (atype < 0)
> -		return -EINVAL;
> +	enum cgroup_bpf_attach_type from_atype, to_atype;
>  
> -	progs = &cgrp->bpf.progs[atype];
> -	flags = cgrp->bpf.flags[atype];
> +	if (type == BPF_LSM_CGROUP) {
> +		from_atype = CGROUP_LSM_START;
> +		to_atype = CGROUP_LSM_END;
Enforce prog_attach_flags for BPF_LSM_CGROUP:

		if (total_cnt && !prog_attach_flags)
			return -EINVAL;
			
> +	} else {
> +		from_atype = to_cgroup_bpf_attach_type(type);
> +		if (from_atype < 0)
> +			return -EINVAL;
> +		to_atype = from_atype;
> +	}
>  
> -	effective = rcu_dereference_protected(cgrp->bpf.effective[atype],
> -					      lockdep_is_held(&cgroup_mutex));
> +	for (atype = from_atype; atype <= to_atype; atype++) {
> +		progs = &cgrp->bpf.progs[atype];
> +		flags = cgrp->bpf.flags[atype];
>  
> -	if (attr->query.query_flags & BPF_F_QUERY_EFFECTIVE)
> -		cnt = bpf_prog_array_length(effective);
> -	else
> -		cnt = prog_list_length(progs);
> +		effective = rcu_dereference_protected(cgrp->bpf.effective[atype],
> +						      lockdep_is_held(&cgroup_mutex));
nit. This can be done under the BPF_F_QUERY_EFFECTIVE case below.

>  
> -	if (copy_to_user(&uattr->query.attach_flags, &flags, sizeof(flags)))
> -		return -EFAULT;
> -	if (copy_to_user(&uattr->query.prog_cnt, &cnt, sizeof(cnt)))
> +		if (attr->query.query_flags & BPF_F_QUERY_EFFECTIVE)
> +			total_cnt += bpf_prog_array_length(effective);
> +		else
> +			total_cnt += prog_list_length(progs);
> +	}
> +
> +	if (type != BPF_LSM_CGROUP)
> +		if (copy_to_user(&uattr->query.attach_flags, &flags, sizeof(flags)))
> +			return -EFAULT;
nit. Move this copy_to_user(&uattr->query.attach_flags,...) to the
'if (type == BPF_LSM_CGROUP) { from_atype = .... } else { ... }' above.
That will save a BPF_LSM_CGROUP test.

I think the '== BPF_LSM_CGROUP' case needs to copy a 0 to user also.

> +	if (copy_to_user(&uattr->query.prog_cnt, &total_cnt, sizeof(total_cnt)))
>  		return -EFAULT;
> -	if (attr->query.prog_cnt == 0 || !prog_ids || !cnt)
> +	if (attr->query.prog_cnt == 0 || !prog_ids || !total_cnt)
>  		/* return early if user requested only program count + flags */
>  		return 0;
> -	if (attr->query.prog_cnt < cnt) {
> -		cnt = attr->query.prog_cnt;
> +
> +	if (attr->query.prog_cnt < total_cnt) {
> +		total_cnt = attr->query.prog_cnt;
>  		ret = -ENOSPC;
>  	}
>  
> -	if (attr->query.query_flags & BPF_F_QUERY_EFFECTIVE) {
> -		return bpf_prog_array_copy_to_user(effective, prog_ids, cnt);
> -	} else {
> -		struct bpf_prog_list *pl;
> -		u32 id;
> +	for (atype = from_atype; atype <= to_atype; atype++) {
> +		if (total_cnt <= 0)
nit. total_cnt cannot be -ve ?
!total_cnt instead ?
and may be do it in the for-loop test.

> +			break;
>  
> -		i = 0;
> -		hlist_for_each_entry(pl, progs, node) {
> -			prog = prog_list_prog(pl);
> -			id = prog->aux->id;
> -			if (copy_to_user(prog_ids + i, &id, sizeof(id)))
> -				return -EFAULT;
> -			if (++i == cnt)
> -				break;
> +		progs = &cgrp->bpf.progs[atype];
> +		flags = cgrp->bpf.flags[atype];
> +
> +		effective = rcu_dereference_protected(cgrp->bpf.effective[atype],
> +						      lockdep_is_held(&cgroup_mutex));
nit. This can be done under the BPF_F_QUERY_EFFECTIVE case below.

> +
> +		if (attr->query.query_flags & BPF_F_QUERY_EFFECTIVE)
> +			cnt = bpf_prog_array_length(effective);
> +		else
> +			cnt = prog_list_length(progs);
> +
> +		if (cnt >= total_cnt)
> +			cnt = total_cnt;
nit. This seems to be the only reason that
the "if (attr->query.query_flags & BPF_F_QUERY_EFFECTIVE)"
need to be broken up into two halves.  One above and one below.
It does not save much code.  How about repeating this one line
'cnt = min_t(int, cnt, total_cnt);' instead ?

> +
> +		if (attr->query.query_flags & BPF_F_QUERY_EFFECTIVE) {
> +			ret = bpf_prog_array_copy_to_user(effective, prog_ids, cnt);
> +		} else {
> +			struct bpf_prog_list *pl;
> +			u32 id;
> +
> +			i = 0;
> +			hlist_for_each_entry(pl, progs, node) {
> +				prog = prog_list_prog(pl);
> +				id = prog->aux->id;
> +				if (copy_to_user(prog_ids + i, &id, sizeof(id)))
> +					return -EFAULT;
> +				if (++i == cnt)
> +					break;
> +			}
>  		}
> +
> +		if (prog_attach_flags)
> +			for (i = 0; i < cnt; i++)
> +				if (copy_to_user(prog_attach_flags + i, &flags, sizeof(flags)))
> +					return -EFAULT;
> +
> +		prog_ids += cnt;
> +		total_cnt -= cnt;
> +		if (prog_attach_flags)
> +			prog_attach_flags += cnt;
nit. Merge this into the above "if (prog_attach_flags)" case.

>  	}
>  	return ret;
>  }
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index a237be4f8bb3..27492d44133f 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -3520,7 +3520,7 @@ static int bpf_prog_detach(const union bpf_attr *attr)
>  	}
>  }
>  
> -#define BPF_PROG_QUERY_LAST_FIELD query.prog_cnt
> +#define BPF_PROG_QUERY_LAST_FIELD query.prog_attach_flags
>  
>  static int bpf_prog_query(const union bpf_attr *attr,
>  			  union bpf_attr __user *uattr)
> @@ -3556,6 +3556,7 @@ static int bpf_prog_query(const union bpf_attr *attr,
>  	case BPF_CGROUP_SYSCTL:
>  	case BPF_CGROUP_GETSOCKOPT:
>  	case BPF_CGROUP_SETSOCKOPT:
> +	case BPF_LSM_CGROUP:
>  		return cgroup_bpf_prog_query(attr, uattr);
>  	case BPF_LIRC_MODE2:
>  		return lirc_prog_query(attr, uattr);
> @@ -4066,6 +4067,9 @@ static int bpf_prog_get_info_by_fd(struct file *file,
>  
>  	if (prog->aux->btf)
>  		info.btf_id = btf_obj_id(prog->aux->btf);
> +	info.attach_btf_id = prog->aux->attach_btf_id;
> +	if (prog->aux->attach_btf)
> +		info.attach_btf_obj_id = btf_obj_id(prog->aux->attach_btf);
Need this also:

	else if (prog->aux->dst_prog)
		info.attach_btf_obj_id = btf_obj_id(prog->aux->dst_prog->aux->attach_btf);

>  
>  	ulen = info.nr_func_info;
>  	info.nr_func_info = prog->aux->func_info_cnt;
> -- 
> 2.36.1.255.ge46751e96f-goog
> 



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