bpf: add MAP_LOOKUP_AND_DELETE_ELEM syscall

The previous patch implemented a bpf queue/stack maps that
provided the peek/pop/push functions.  There is not a direct
relationship between those functions and the current maps
syscalls, hence a new MAP_LOOKUP_AND_DELETE_ELEM syscall is added,
this is mapped to the pop operation in the queue/stack maps
and it is still to implement in other kind of maps.

Signed-off-by: Mauricio Vasquez B <mauricio.vasquez@polito.it>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

include/uapi/linux/bpf.h

@@ -103,6 +103,7 @@ enum bpf_cmd {
 	BPF_BTF_LOAD,
 	BPF_BTF_GET_FD_BY_ID,
 	BPF_TASK_FD_QUERY,
+	BPF_MAP_LOOKUP_AND_DELETE_ELEM,
 };
 
 enum bpf_map_type {

kernel/bpf/syscall.c

@@ -999,6 +999,69 @@ err_put:
 	return err;
 }
 
+#define BPF_MAP_LOOKUP_AND_DELETE_ELEM_LAST_FIELD value
+
+static int map_lookup_and_delete_elem(union bpf_attr *attr)
+{
+	void __user *ukey = u64_to_user_ptr(attr->key);
+	void __user *uvalue = u64_to_user_ptr(attr->value);
+	int ufd = attr->map_fd;
+	struct bpf_map *map;
+	void *key, *value, *ptr;
+	u32 value_size;
+	struct fd f;
+	int err;
+
+	if (CHECK_ATTR(BPF_MAP_LOOKUP_AND_DELETE_ELEM))
+		return -EINVAL;
+
+	f = fdget(ufd);
+	map = __bpf_map_get(f);
+	if (IS_ERR(map))
+		return PTR_ERR(map);
+
+	if (!(f.file->f_mode & FMODE_CAN_WRITE)) {
+		err = -EPERM;
+		goto err_put;
+	}
+
+	key = __bpf_copy_key(ukey, map->key_size);
+	if (IS_ERR(key)) {
+		err = PTR_ERR(key);
+		goto err_put;
+	}
+
+	value_size = map->value_size;
+
+	err = -ENOMEM;
+	value = kmalloc(value_size, GFP_USER | __GFP_NOWARN);
+	if (!value)
+		goto free_key;
+
+	if (map->map_type == BPF_MAP_TYPE_QUEUE ||
+	    map->map_type == BPF_MAP_TYPE_STACK) {
+		err = map->ops->map_pop_elem(map, value);
+	} else {
+		err = -ENOTSUPP;
+	}
+
+	if (err)
+		goto free_value;
+
+	if (copy_to_user(uvalue, value, value_size) != 0)
+		goto free_value;
+
+	err = 0;
+
+free_value:
+	kfree(value);
+free_key:
+	kfree(key);
+err_put:
+	fdput(f);
+	return err;
+}
+
 static const struct bpf_prog_ops * const bpf_prog_types[] = {
 #define BPF_PROG_TYPE(_id, _name) \
 	[_id] = & _name ## _prog_ops,
@@ -2472,6 +2535,9 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, siz
 	case BPF_TASK_FD_QUERY:
 		err = bpf_task_fd_query(&attr, uattr);
 		break;
+	case BPF_MAP_LOOKUP_AND_DELETE_ELEM:
+		err = map_lookup_and_delete_elem(&attr);
+		break;
 	default:
 		err = -EINVAL;
 		break;