Add bpf_lua_tostring function

Author: VictorNogueiraRio

include/uapi/linux/bpf.h

@@ -2967,6 +2967,15 @@ union bpf_attr {
  *		The converted Lua value at the given index, if the value is
  *		convertible to an integer(see the Lua manual for more details
  *		on type conversion); otherwise returns 0
+ *
+ * void bpf_lua_tostring(void *ctx, const char *str, u32 size, int index)
+ *	Description
+ *		Converts the Lua value at the given index of the Lua
+ *		stack to a C string and copies size bytes of it to
+ *		value pointed by str
+ *	Return
+ *		1 if the value at the given index of the Lua stack is a
+ *		string; otherwise it returns 0
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -3101,7 +3110,8 @@ union bpf_attr {
 	FN(lua_pushstring),		\
 	FN(lua_toboolean),		\
 	FN(lua_tointeger),		\
-	FN(lua_newpacket),
+	FN(lua_newpacket),		\
+	FN(lua_tostring),
 	/* #endif CONFIG_XDP_LUA */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper

net/core/filter.c

@@ -6092,6 +6092,26 @@ static const struct bpf_func_proto bpf_lua_newpacket_proto = {
 	.arg1_type	= ARG_PTR_TO_CTX,
 	.arg2_type	= ARG_ANYTHING,
 };
+
+BPF_CALL_4(bpf_lua_tostring, struct xdp_buff *, ctx, char *, str, u32, size, int, index) {
+	if (lua_isstring(ctx->L, index)) {
+		strncpy(str, lua_tostring(ctx->L, index), size);
+		return 1;
+	}
+
+	return 0;
+}
+
+static const struct bpf_func_proto bpf_lua_tostring_proto = {
+	.func		= bpf_lua_tostring,
+	.gpl_only	= false,
+	.pkt_access	= false,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_PTR_TO_CTX,
+	.arg2_type	= ARG_PTR_TO_UNINIT_MEM,
+	.arg3_type	= ARG_CONST_SIZE,
+	.arg4_type	= ARG_ANYTHING,
+};
 #endif /* CONFIG_XDP_LUA */
 
 bool bpf_helper_changes_pkt_data(void *func)
@@ -6197,6 +6217,8 @@ bpf_base_func_proto(enum bpf_func_id func_id)
 		return &bpf_lua_tointeger_proto;
 	case BPF_FUNC_lua_newpacket:
 		return &bpf_lua_newpacket_proto;
+	case BPF_FUNC_lua_tostring:
+		return &bpf_lua_tostring_proto;
 #endif /* CONFIG_XDP_LUA */
 	default:
 		return NULL;

tools/include/uapi/linux/bpf.h

@@ -2972,6 +2972,15 @@ union bpf_attr {
  *	Description
  *		Create new luaunpack user data buffer pointing to
  *		the captured packet at the specified offset
+ *
+ * void bpf_lua_tostring(void *ctx, const char *str, u32 size, int index)
+ *	Description
+ *		Converts the Lua value at the given index of the Lua
+ *		stack to a C string and copies size bytes of it to
+ *		value pointed by str
+ *	Return
+ *		1 if the value at the given index of the Lua stack is a
+ *		string; otherwise it returns 0
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -3106,7 +3115,8 @@ union bpf_attr {
 	FN(lua_pushstring),		\
 	FN(lua_toboolean),		\
 	FN(lua_tointeger),		\
-	FN(lua_newpacket),
+	FN(lua_newpacket),		\
+	FN(lua_tostring),
 	/* #endif CONFIG_XDP_LUA */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper