bpf: Add BPF_OBJ_GET_INFO_BY_FD

A single BPF_OBJ_GET_INFO_BY_FD cmd is used to obtain the info
for both bpf_prog and bpf_map.  The kernel can figure out the
fd is associated with a bpf_prog or bpf_map.

The suggested struct bpf_prog_info and struct bpf_map_info are
not meant to be a complete list and it is not the goal of this patch.
New fields can be added in the future patch.

The focus of this patch is to create the interface,
BPF_OBJ_GET_INFO_BY_FD cmd for exposing the bpf_prog's and
bpf_map's info.

The obj's info, which will be extended (and get bigger) over time, is
separated from the bpf_attr to avoid bloating the bpf_attr.

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Alexei Starovoitov <ast@fb.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 146 insertions, 17 deletions

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 1802bb9c47d9..8942c820d620 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -1239,6 +1239,145 @@ static int bpf_map_get_fd_by_id(const union bpf_attr *attr)
 	return fd;
 }
 
+static int check_uarg_tail_zero(void __user *uaddr,
+				size_t expected_size,
+				size_t actual_size)
+{
+	unsigned char __user *addr;
+	unsigned char __user *end;
+	unsigned char val;
+	int err;
+
+	if (actual_size <= expected_size)
+		return 0;
+
+	addr = uaddr + expected_size;
+	end  = uaddr + actual_size;
+
+	for (; addr < end; addr++) {
+		err = get_user(val, addr);
+		if (err)
+			return err;
+		if (val)
+			return -E2BIG;
+	}
+
+	return 0;
+}
+
+static int bpf_prog_get_info_by_fd(struct bpf_prog *prog,
+				   const union bpf_attr *attr,
+				   union bpf_attr __user *uattr)
+{
+	struct bpf_prog_info __user *uinfo = u64_to_user_ptr(attr->info.info);
+	struct bpf_prog_info info = {};
+	u32 info_len = attr->info.info_len;
+	char __user *uinsns;
+	u32 ulen;
+	int err;
+
+	err = check_uarg_tail_zero(uinfo, sizeof(info), info_len);
+	if (err)
+		return err;
+	info_len = min_t(u32, sizeof(info), info_len);
+
+	if (copy_from_user(&info, uinfo, info_len))
+		return err;
+
+	info.type = prog->type;
+	info.id = prog->aux->id;
+
+	memcpy(info.tag, prog->tag, sizeof(prog->tag));
+
+	if (!capable(CAP_SYS_ADMIN)) {
+		info.jited_prog_len = 0;
+		info.xlated_prog_len = 0;
+		goto done;
+	}
+
+	ulen = info.jited_prog_len;
+	info.jited_prog_len = prog->jited_len;
+	if (info.jited_prog_len && ulen) {
+		uinsns = u64_to_user_ptr(info.jited_prog_insns);
+		ulen = min_t(u32, info.jited_prog_len, ulen);
+		if (copy_to_user(uinsns, prog->bpf_func, ulen))
+			return -EFAULT;
+	}
+
+	ulen = info.xlated_prog_len;
+	info.xlated_prog_len = bpf_prog_size(prog->len);
+	if (info.xlated_prog_len && ulen) {
+		uinsns = u64_to_user_ptr(info.xlated_prog_insns);
+		ulen = min_t(u32, info.xlated_prog_len, ulen);
+		if (copy_to_user(uinsns, prog->insnsi, ulen))
+			return -EFAULT;
+	}
+
+done:
+	if (copy_to_user(uinfo, &info, info_len) ||
+	    put_user(info_len, &uattr->info.info_len))
+		return -EFAULT;
+
+	return 0;
+}
+
+static int bpf_map_get_info_by_fd(struct bpf_map *map,
+				  const union bpf_attr *attr,
+				  union bpf_attr __user *uattr)
+{
+	struct bpf_map_info __user *uinfo = u64_to_user_ptr(attr->info.info);
+	struct bpf_map_info info = {};
+	u32 info_len = attr->info.info_len;
+	int err;
+
+	err = check_uarg_tail_zero(uinfo, sizeof(info), info_len);
+	if (err)
+		return err;
+	info_len = min_t(u32, sizeof(info), info_len);
+
+	info.type = map->map_type;
+	info.id = map->id;
+	info.key_size = map->key_size;
+	info.value_size = map->value_size;
+	info.max_entries = map->max_entries;
+	info.map_flags = map->map_flags;
+
+	if (copy_to_user(uinfo, &info, info_len) ||
+	    put_user(info_len, &uattr->info.info_len))
+		return -EFAULT;
+
+	return 0;
+}
+
+#define BPF_OBJ_GET_INFO_BY_FD_LAST_FIELD info.info
+
+static int bpf_obj_get_info_by_fd(const union bpf_attr *attr,
+				  union bpf_attr __user *uattr)
+{
+	int ufd = attr->info.bpf_fd;
+	struct fd f;
+	int err;
+
+	if (CHECK_ATTR(BPF_OBJ_GET_INFO_BY_FD))
+		return -EINVAL;
+
+	f = fdget(ufd);
+	if (!f.file)
+		return -EBADFD;
+
+	if (f.file->f_op == &bpf_prog_fops)
+		err = bpf_prog_get_info_by_fd(f.file->private_data, attr,
+					      uattr);
+	else if (f.file->f_op == &bpf_map_fops)
+		err = bpf_map_get_info_by_fd(f.file->private_data, attr,
+					     uattr);
+	else
+		err = -EINVAL;
+
+	fdput(f);
+	return err;
+}
+
 SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, size)
 {
 	union bpf_attr attr = {};
@@ -1258,23 +1397,10 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, siz
 	 * user-space does not rely on any kernel feature
 	 * extensions we dont know about yet.
 	 */
-	if (size > sizeof(attr)) {
-		unsigned char __user *addr;
-		unsigned char __user *end;
-		unsigned char val;
-
-		addr = (void __user *)uattr + sizeof(attr);
-		end  = (void __user *)uattr + size;
-
-		for (; addr < end; addr++) {
-			err = get_user(val, addr);
-			if (err)
-				return err;
-			if (val)
-				return -E2BIG;
-		}
-		size = sizeof(attr);
-	}
+	err = check_uarg_tail_zero(uattr, sizeof(attr), size);
+	if (err)
+		return err;
+	size = min_t(u32, size, sizeof(attr));
 
 	/* copy attributes from user space, may be less than sizeof(bpf_attr) */
 	if (copy_from_user(&attr, uattr, size) != 0)
@@ -1330,6 +1456,9 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, siz
 	case BPF_MAP_GET_FD_BY_ID:
 		err = bpf_map_get_fd_by_id(&attr);
 		break;
+	case BPF_OBJ_GET_INFO_BY_FD:
+		err = bpf_obj_get_info_by_fd(&attr, uattr);
+		break;
 	default:
 		err = -EINVAL;
 		break;