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Commit f4324551 authored by Daniel Mack's avatar Daniel Mack Committed by David S. Miller
Browse files

bpf: add BPF_PROG_ATTACH and BPF_PROG_DETACH commands 



Extend the bpf(2) syscall by two new commands, BPF_PROG_ATTACH and
BPF_PROG_DETACH which allow attaching and detaching eBPF programs
to a target.

On the API level, the target could be anything that has an fd in
userspace, hence the name of the field in union bpf_attr is called
'target_fd'.

When called with BPF_ATTACH_TYPE_CGROUP_INET_{E,IN}GRESS, the target is
expected to be a valid file descriptor of a cgroup v2 directory which
has the bpf controller enabled. These are the only use-cases
implemented by this patch at this point, but more can be added.

If a program of the given type already exists in the given cgroup,
the program is swapped automically, so userspace does not have to drop
an existing program first before installing a new one, which would
otherwise leave a gap in which no program is attached.

For more information on the propagation logic to subcgroups, please
refer to the bpf cgroup controller implementation.

The API is guarded by CAP_NET_ADMIN.

Signed-off-by: default avatarDaniel Mack <daniel@zonque.org>
Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 30070984

include/uapi/linux/bpf.h

+8 −0
Original line number Diff line number Diff line
@@ -73,6 +73,8 @@ enum bpf_cmd { 
	BPF_PROG_LOAD,

	BPF_OBJ_PIN,

	BPF_OBJ_GET,

	BPF_PROG_ATTACH,

	BPF_PROG_DETACH,

};



enum bpf_map_type {
@@ -159,6 +161,12 @@ union bpf_attr { 
		__aligned_u64	pathname;

		__u32		bpf_fd;

	};



	struct { /* anonymous struct used by BPF_PROG_ATTACH/DETACH commands */

		__u32		target_fd;	/* container object to attach to */

		__u32		attach_bpf_fd;	/* eBPF program to attach */

		__u32		attach_type;

	};

} __attribute__((aligned(8)));



/* BPF helper function descriptions:

kernel/bpf/syscall.c

+81 −0
Original line number Diff line number Diff line
@@ -835,6 +835,77 @@ static int bpf_obj_get(const union bpf_attr *attr) 
	return bpf_obj_get_user(u64_to_user_ptr(attr->pathname));

}



#ifdef CONFIG_CGROUP_BPF



#define BPF_PROG_ATTACH_LAST_FIELD attach_type



static int bpf_prog_attach(const union bpf_attr *attr)

{

	struct bpf_prog *prog;

	struct cgroup *cgrp;



	if (!capable(CAP_NET_ADMIN))

		return -EPERM;



	if (CHECK_ATTR(BPF_PROG_ATTACH))

		return -EINVAL;



	switch (attr->attach_type) {

	case BPF_CGROUP_INET_INGRESS:

	case BPF_CGROUP_INET_EGRESS:

		prog = bpf_prog_get_type(attr->attach_bpf_fd,

					 BPF_PROG_TYPE_CGROUP_SKB);

		if (IS_ERR(prog))

			return PTR_ERR(prog);



		cgrp = cgroup_get_from_fd(attr->target_fd);

		if (IS_ERR(cgrp)) {

			bpf_prog_put(prog);

			return PTR_ERR(cgrp);

		}



		cgroup_bpf_update(cgrp, prog, attr->attach_type);

		cgroup_put(cgrp);

		break;



	default:

		return -EINVAL;

	}



	return 0;

}



#define BPF_PROG_DETACH_LAST_FIELD attach_type



static int bpf_prog_detach(const union bpf_attr *attr)

{

	struct cgroup *cgrp;



	if (!capable(CAP_NET_ADMIN))

		return -EPERM;



	if (CHECK_ATTR(BPF_PROG_DETACH))

		return -EINVAL;



	switch (attr->attach_type) {

	case BPF_CGROUP_INET_INGRESS:

	case BPF_CGROUP_INET_EGRESS:

		cgrp = cgroup_get_from_fd(attr->target_fd);

		if (IS_ERR(cgrp))

			return PTR_ERR(cgrp);



		cgroup_bpf_update(cgrp, NULL, attr->attach_type);

		cgroup_put(cgrp);

		break;



	default:

		return -EINVAL;

	}



	return 0;

}

#endif /* CONFIG_CGROUP_BPF */



SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, size)

{

	union bpf_attr attr = {};
@@ -901,6 +972,16 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, siz 
	case BPF_OBJ_GET:

		err = bpf_obj_get(&attr);

		break;



#ifdef CONFIG_CGROUP_BPF

	case BPF_PROG_ATTACH:

		err = bpf_prog_attach(&attr);

		break;

	case BPF_PROG_DETACH:

		err = bpf_prog_detach(&attr);

		break;

#endif



	default:

		err = -EINVAL;

		break;