bpf: Free special fields when update hash maps with BPF_F_LOCK

When updating hash maps with BPF_F_LOCK, the special fields were not
freed after being replaced. This could cause memory referenced by
BPF_KPTR_{REF,PERCPU} fields to be held until the map gets freed.

Fix this by calling 'check_and_free_fields()' after
'copy_map_value_locked()' to properly release the old fields.

Fixes: 14a324f ("bpf: Wire up freeing of referenced kptr")
Signed-off-by: Leon Hwang <[email protected]>

Author: Asphaltt

kernel/bpf/hashtab.c

@@ -1124,6 +1124,7 @@ static long htab_map_update_elem(struct bpf_map *map, void *key, void *value,
 			copy_map_value_locked(map,
 					      htab_elem_value(l_old, key_size),
 					      value, false);
+			check_and_free_fields(htab, l_old);
 			return 0;
 		}
 		/* fall through, grab the bucket lock and lookup again.
@@ -1152,6 +1153,7 @@ static long htab_map_update_elem(struct bpf_map *map, void *key, void *value,
 		copy_map_value_locked(map,
 				      htab_elem_value(l_old, key_size),
 				      value, false);
+		check_and_free_fields(htab, l_old);
 		ret = 0;
 		goto err;
 	}