bpf: Add map_name to bpf_map_info

This patch allows userspace to specify a name for a map
during BPF_MAP_CREATE.

The map's name can later be exported to user space
via BPF_OBJ_GET_INFO_BY_FD.
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>

include/linux/bpf.h

@@ -56,6 +56,7 @@ struct bpf_map {
 	struct work_struct work;
 	atomic_t usercnt;
 	struct bpf_map *inner_map_meta;
+	u8 name[BPF_OBJ_NAME_LEN];
 };
 
 /* function argument constraints */

include/uapi/linux/bpf.h

@@ -190,6 +190,7 @@ union bpf_attr {
 		__u32	numa_node;	/* numa node (effective only if
 					 * BPF_F_NUMA_NODE is set).
 					 */
+		__u8	map_name[BPF_OBJ_NAME_LEN];
 	};
 
 	struct { /* anonymous struct used by BPF_MAP_*_ELEM commands */
@@ -829,6 +830,7 @@ struct bpf_map_info {
 	__u32 value_size;
 	__u32 max_entries;
 	__u32 map_flags;
+	__u8  name[BPF_OBJ_NAME_LEN];
 } __attribute__((aligned(8)));
 
 /* User bpf_sock_ops struct to access socket values and specify request ops

kernel/bpf/syscall.c

@@ -339,7 +339,7 @@ static int bpf_obj_name_cpy(char *dst, const char *src)
 	return 0;
 }
 
-#define BPF_MAP_CREATE_LAST_FIELD numa_node
+#define BPF_MAP_CREATE_LAST_FIELD map_name
 /* called via syscall */
 static int map_create(union bpf_attr *attr)
 {
@@ -361,6 +361,10 @@ static int map_create(union bpf_attr *attr)
 	if (IS_ERR(map))
 		return PTR_ERR(map);
 
+	err = bpf_obj_name_cpy(map->name, attr->map_name);
+	if (err)
+		goto free_map_nouncharge;
+
 	atomic_set(&map->refcnt, 1);
 	atomic_set(&map->usercnt, 1);
 
@@ -1462,6 +1466,7 @@ static int bpf_map_get_info_by_fd(struct bpf_map *map,
 	info.value_size = map->value_size;
 	info.max_entries = map->max_entries;
 	info.map_flags = map->map_flags;
+	memcpy(info.name, map->name, sizeof(map->name));
 
 	if (copy_to_user(uinfo, &info, info_len) ||
 	    put_user(info_len, &uattr->info.info_len))