[RFC PATCH bpf-next 11/16] bpf: implement query for target_proto and file dumper prog_id

[Yonghong Song <yhs@fb.com>]

Given a fd representing a bpfdump target, user
can retrieve the target_proto name which represents
the bpf program prototype.

Given a fd representing a file dumper, user can
retrieve the bpf_prog id associated with that dumper.

Signed-off-by: Yonghong Song <yhs@fb.com>
---
 include/linux/bpf.h            |  1 +
 include/uapi/linux/bpf.h       | 13 +++++++++
 kernel/bpf/dump.c              | 51 ++++++++++++++++++++++++++++++++++
 kernel/bpf/syscall.c           | 14 ++++++++++
 tools/include/uapi/linux/bpf.h | 13 +++++++++
 5 files changed, 92 insertions(+)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index f7d4269d77b8..c9aec3b02dfa 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1120,6 +1120,7 @@ int bpf_dump_create(u32 prog_fd, const char __user *dumper_name);
 struct bpf_prog *bpf_dump_get_prog(struct seq_file *seq, u32 priv_data_size,
 				   u64 *seq_num);
 int bpf_dump_run_prog(struct bpf_prog *prog, void *ctx);
+int bpf_dump_query(const union bpf_attr *attr, union bpf_attr __user *uattr);
 
 int bpf_percpu_hash_copy(struct bpf_map *map, void *key, void *value);
 int bpf_percpu_array_copy(struct bpf_map *map, void *key, void *value);
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index a245f0df53c4..fc2157e319f1 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -113,6 +113,7 @@ enum bpf_cmd {
 	BPF_MAP_DELETE_BATCH,
 	BPF_LINK_CREATE,
 	BPF_LINK_UPDATE,
+	BPF_DUMP_QUERY,
 };
 
 enum bpf_map_type {
@@ -594,6 +595,18 @@ union bpf_attr {
 		__u32		old_prog_fd;
 	} link_update;
 
+	struct {
+		__u32		query_fd;
+		__u32		flags;
+		union {
+			struct {
+				__aligned_u64	target_proto;
+				__u32		proto_buf_len;
+			};
+			__u32			prog_id;
+		};
+	} dump_query;
+
 } __attribute__((aligned(8)));
 
 /* The description below is an attempt at providing documentation to eBPF
diff --git a/kernel/bpf/dump.c b/kernel/bpf/dump.c
index 4e009b2612c2..f3041b362057 100644
--- a/kernel/bpf/dump.c
+++ b/kernel/bpf/dump.c
@@ -86,6 +86,57 @@ static void *get_extra_priv_dptr(void *old_ptr, u32 old_size)
 	return old_ptr + roundup(old_size, 8);
 }
 
+int bpf_dump_query(const union bpf_attr *attr, union bpf_attr __user *uattr)
+{
+	struct bpfdump_target_info *tinfo;
+	struct dumper_inode_info *i_info;
+	const char *target_proto;
+	void * __user proto_buf;
+	struct file *filp;
+	u32 proto_len;
+	struct fd qfd;
+	int err = 0;
+
+	if (attr->dump_query.flags != 0)
+		return -EINVAL;
+
+	qfd = fdget(attr->dump_query.query_fd);
+	filp = qfd.file;
+	if (!filp)
+		return -EBADF;
+
+	if (filp->f_op != &bpf_dumper_ops &&
+	    filp->f_inode->i_op != &bpf_dir_iops) {
+		err = -EINVAL;
+		goto done;
+	}
+
+	if (filp->f_op == &bpf_dumper_ops) {
+		i_info = filp->f_inode->i_private;
+		if (put_user(i_info->prog->aux->id, &uattr->dump_query.prog_id))
+			err = -EFAULT;
+
+		goto done;
+	}
+
+	tinfo = filp->f_inode->i_private;
+	target_proto = tinfo->target_proto;
+
+	proto_len = strlen(target_proto) + 1;
+	if (attr->dump_query.proto_buf_len < proto_len) {
+		err = -ENOSPC;
+		goto done;
+	}
+
+	proto_buf = u64_to_user_ptr(attr->dump_query.target_proto);
+	if (copy_to_user(proto_buf, target_proto, proto_len))
+		err = -EFAULT;
+
+done:
+	fdput(qfd);
+	return err;
+}
+
 #ifdef CONFIG_PROC_FS
 static void dumper_show_fdinfo(struct seq_file *m, struct file *filp)
 {
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 62a872a406ca..46b58f1f2d75 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -3673,6 +3673,17 @@ static int link_update(union bpf_attr *attr)
 	return ret;
 }
 
+#define BPF_DUMP_QUERY_LAST_FIELD dump_query.proto_buf_len
+
+static int bpf_dump_do_query(const union bpf_attr *attr,
+			     union bpf_attr __user *uattr)
+{
+	if (CHECK_ATTR(BPF_DUMP_QUERY))
+		return -EINVAL;
+
+	return bpf_dump_query(attr, uattr);
+}
+
 SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, size)
 {
 	union bpf_attr attr;
@@ -3790,6 +3801,9 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, siz
 	case BPF_LINK_UPDATE:
 		err = link_update(&attr);
 		break;
+	case BPF_DUMP_QUERY:
+		err = bpf_dump_do_query(&attr, uattr);
+		break;
 	default:
 		err = -EINVAL;
 		break;
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index a245f0df53c4..fc2157e319f1 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -113,6 +113,7 @@ enum bpf_cmd {
 	BPF_MAP_DELETE_BATCH,
 	BPF_LINK_CREATE,
 	BPF_LINK_UPDATE,
+	BPF_DUMP_QUERY,
 };
 
 enum bpf_map_type {
@@ -594,6 +595,18 @@ union bpf_attr {
 		__u32		old_prog_fd;
 	} link_update;
 
+	struct {
+		__u32		query_fd;
+		__u32		flags;
+		union {
+			struct {
+				__aligned_u64	target_proto;
+				__u32		proto_buf_len;
+			};
+			__u32			prog_id;
+		};
+	} dump_query;
+
 } __attribute__((aligned(8)));
 
 /* The description below is an attempt at providing documentation to eBPF
-- 
2.24.1