bpf: add support for sockmap detach programs

The bpf map sockmap supports adding programs via attach commands. This
patch adds the detach command to keep the API symmetric and allow
users to remove previously added programs. Otherwise the user would
have to delete the map and re-add it to get in this state.

This also adds a series of additional tests to capture detach operation
and also attaching/detaching invalid prog types.

API note: socks will run (or not run) programs depending on the state
of the map at the time the sock is added. We do not for example walk
the map and remove programs from previously attached socks.

Acked-by: Daniel Borkmann <[e-mail]>
Signed-off-by: John Fastabend <[e-mail]>
Acked-by: Alexei Starovoitov <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/linux/bpf.h

···
 
 #if defined(CONFIG_STREAM_PARSER) && defined(CONFIG_BPF_SYSCALL)
 struct sock  *__sock_map_lookup_elem(struct bpf_map *map, u32 key);
-int sock_map_attach_prog(struct bpf_map *map, struct bpf_prog *prog, u32 type);
+int sock_map_prog(struct bpf_map *map, struct bpf_prog *prog, u32 type);
 #else
 static inline struct sock  *__sock_map_lookup_elem(struct bpf_map *map, u32 key)
 {
 	return NULL;
 }
 
-static inline int sock_map_attach_prog(struct bpf_map *map,
-				       struct bpf_prog *prog,
-				       u32 type)
+static inline int sock_map_prog(struct bpf_map *map,
+				struct bpf_prog *prog,
+				u32 type)
 {
 	return -EOPNOTSUPP;
 }

kernel/bpf/sockmap.c

···
 	return err;
 }
 
-int sock_map_attach_prog(struct bpf_map *map, struct bpf_prog *prog, u32 type)
+int sock_map_prog(struct bpf_map *map, struct bpf_prog *prog, u32 type)
 {
 	struct bpf_stab *stab = container_of(map, struct bpf_stab, map);
 	struct bpf_prog *orig;

kernel/bpf/syscall.c

···
 
 #define BPF_PROG_ATTACH_LAST_FIELD attach_flags
 
-static int sockmap_get_from_fd(const union bpf_attr *attr)
+static int sockmap_get_from_fd(const union bpf_attr *attr, bool attach)
 {
+	struct bpf_prog *prog = NULL;
 	int ufd = attr->target_fd;
-	struct bpf_prog *prog;
 	struct bpf_map *map;
 	struct fd f;
 	int err;
···
 	if (IS_ERR(map))
 		return PTR_ERR(map);
 
-	prog = bpf_prog_get_type(attr->attach_bpf_fd, BPF_PROG_TYPE_SK_SKB);
-	if (IS_ERR(prog)) {
-		fdput(f);
-		return PTR_ERR(prog);
+	if (attach) {
+		prog = bpf_prog_get_type(attr->attach_bpf_fd,
+					 BPF_PROG_TYPE_SK_SKB);
+		if (IS_ERR(prog)) {
+			fdput(f);
+			return PTR_ERR(prog);
+		}
 	}
 
-	err = sock_map_attach_prog(map, prog, attr->attach_type);
+	err = sock_map_prog(map, prog, attr->attach_type);
 	if (err) {
 		fdput(f);
-		bpf_prog_put(prog);
+		if (prog)
+			bpf_prog_put(prog);
 		return err;
 	}
 
···
 		break;
 	case BPF_SK_SKB_STREAM_PARSER:
 	case BPF_SK_SKB_STREAM_VERDICT:
-		return sockmap_get_from_fd(attr);
+		return sockmap_get_from_fd(attr, true);
 	default:
 		return -EINVAL;
 	}
···
 		ret = cgroup_bpf_update(cgrp, NULL, attr->attach_type, false);
 		cgroup_put(cgrp);
 		break;
-
+	case BPF_SK_SKB_STREAM_PARSER:
+	case BPF_SK_SKB_STREAM_VERDICT:
+		ret = sockmap_get_from_fd(attr, false);
+		break;
 	default:
 		return -EINVAL;
 	}

tools/testing/selftests/bpf/test_maps.c

···
 		}
 	}
 
-	/* Test attaching bad fds */
+	/* Test attaching/detaching bad fds */
 	err = bpf_prog_attach(-1, fd, BPF_SK_SKB_STREAM_PARSER, 0);
 	if (!err) {
 		printf("Failed invalid parser prog attach\n");
···
 	err = bpf_prog_attach(-1, fd, BPF_SK_SKB_STREAM_VERDICT, 0);
 	if (!err) {
 		printf("Failed invalid verdict prog attach\n");
+		goto out_sockmap;
+	}
+
+	err = bpf_prog_attach(-1, fd, __MAX_BPF_ATTACH_TYPE, 0);
+	if (!err) {
+		printf("Failed unknown prog attach\n");
+		goto out_sockmap;
+	}
+
+	err = bpf_prog_detach(fd, BPF_SK_SKB_STREAM_PARSER);
+	if (err) {
+		printf("Failed empty parser prog detach\n");
+		goto out_sockmap;
+	}
+
+	err = bpf_prog_detach(fd, BPF_SK_SKB_STREAM_VERDICT);
+	if (err) {
+		printf("Failed empty verdict prog detach\n");
+		goto out_sockmap;
+	}
+
+	err = bpf_prog_detach(fd, __MAX_BPF_ATTACH_TYPE);
+	if (!err) {
+		printf("Detach invalid prog successful\n");
 		goto out_sockmap;
 	}
 
···
 			      BPF_SK_SKB_STREAM_VERDICT, 0);
 	if (err) {
 		printf("Failed stream verdict bpf prog attach\n");
+		goto out_sockmap;
+	}
+
+	err = bpf_prog_attach(verdict_prog, map_fd_rx,
+			      __MAX_BPF_ATTACH_TYPE, 0);
+	if (!err) {
+		printf("Attached unknown bpf prog\n");
 		goto out_sockmap;
 	}
 
···
 
 		assert(waitpid(pid[i], &status, 0) == pid[i]);
 		assert(status == 0);
+	}
+
+	err = bpf_prog_detach(map_fd_rx, __MAX_BPF_ATTACH_TYPE);
+	if (!err) {
+		printf("Detached an invalid prog type.\n");
+		goto out_sockmap;
+	}
+
+	err = bpf_prog_detach(map_fd_rx, BPF_SK_SKB_STREAM_PARSER);
+	if (err) {
+		printf("Failed parser prog detach\n");
+		goto out_sockmap;
+	}
+
+	err = bpf_prog_detach(map_fd_rx, BPF_SK_SKB_STREAM_VERDICT);
+	if (err) {
+		printf("Failed parser prog detach\n");
+		goto out_sockmap;
 	}
 
 	/* Test map close sockets */