add support for AF_PACKET

README.md

@@ -743,6 +743,20 @@ sudo lunatik run examples/keylocker            # runs keylocker
 <↑> <↑> <↓> <↓> <←> <→> <←> <→> <LCTRL> <LALT> # unlocks keyboard
 ```
 
+### tap
+
+[tap](examples/tap.lua)
+is a kernel script that implements a _sniffer_ using `AF_PACKET` socket.
+It prints destination and source MAC addresses followed by Ethernet type and the frame size.
+
+#### Usage
+
+```
+sudo make examples_install    # installs examples
+sudo lunatik run examples/tap # runs tap
+cat /dev/tap
+```
+
 ## References
 
 * [Scriptables Operating Systems with Lua](https://www.netbsd.org/~lneto/dls14.pdf)

examples/tap.lua

@@ -0,0 +1,48 @@
+--
+-- Copyright (c) 2023 ring-0 Ltda.
+--
+-- Permission is hereby granted, free of charge, to any person obtaining
+-- a copy of this software and associated documentation files (the
+-- "Software"), to deal in the Software without restriction, including
+-- without limitation the rights to use, copy, modify, merge, publish,
+-- distribute, sublicense, and/or sell copies of the Software, and to
+-- permit persons to whom the Software is furnished to do so, subject to
+-- the following conditions:
+--
+-- The above copyright notice and this permission notice shall be
+-- included in all copies or substantial portions of the Software.
+--
+-- THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+-- EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+-- MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+-- IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+-- CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+-- TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+-- SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+--
+
+local device = require("device")
+local socket = require("socket")
+local linux  = require("linux")
+
+local PACKET    = socket.af.PACKET
+local RAW       = socket.sock.RAW
+local ETH_P_ALL = 0x0003
+local MTU       = 1500
+
+local function nop() end
+
+local s = linux.stat
+local tap = {name = "tap", open = nop, release = nop, mode = s.IRUGO}
+
+local socket = socket.new(PACKET, RAW, ETH_P_ALL)
+socket:bind(string.pack(">I2", ETH_P_ALL))
+
+function tap:read()
+	local frame = socket:receive(MTU)
+	local dst, src, ethtype = string.unpack(">I6I6I2", frame)
+	return string.format("%X\t%X\t%X\t%d\n", dst, src, ethtype, #frame)
+end
+
+device.new(tap)
+

lib/luasocket.c

@@ -60,18 +60,27 @@ do {						\
 	msg.msg_name = &addr;			\
 } while(0)
 
-static void luasocket_checkaddr(lua_State *L, struct socket *socket, struct sockaddr *addr, int ix)
+#define LUASOCKET_SOCKADDR(addr)	(struct sockaddr *)&addr, sizeof(addr)
+
+#define LUASOCKET_ADDRMAX		(sizeof(struct sockaddr_ll)) /* AF_PACKET */
+#define LUASOCKET_ADDRLEN		(LUASOCKET_ADDRMAX - sizeof(unsigned short))
+typedef struct luasocket_addr_s {
+	unsigned short family;
+	unsigned char data[LUASOCKET_ADDRLEN];
+} luasocket_addr_t;
+
+static void luasocket_checkaddr(lua_State *L, struct socket *socket, luasocket_addr_t *addr, int ix)
 {
-	addr->sa_family = socket->sk->sk_family;
-	if (addr->sa_family == AF_INET) {
+	addr->family = socket->sk->sk_family;
+	if (addr->family == AF_INET) {
 		struct sockaddr_in *addr_in = (struct sockaddr_in *)addr;
 		addr_in->sin_addr.s_addr = htonl((u32)luaL_checkinteger(L, ix));
 		addr_in->sin_port = htons((u16)luaL_checkinteger(L, ix + 1));
 	}
 	else {
 		size_t len;
 		const char *addr_data = luaL_checklstring(L, ix, &len);
-		memcpy(addr->sa_data, addr_data, min(sizeof(addr->sa_data), len));
+		memcpy(addr->data, addr_data, min(LUASOCKET_ADDRLEN, len));
 	}
 }
 
@@ -131,7 +140,7 @@ static int luasocket_send(lua_State *L)
 	vec.iov_len = len;
 
 	if (unlikely(nargs >= 3)) {
-		struct sockaddr addr;
+		luasocket_addr_t addr;
 		luasocket_checkaddr(L, socket, &addr, 3);
 		luasocket_msgaddr(msg, addr);
 	}
@@ -168,10 +177,10 @@ static int luasocket_receive(lua_State *L)
 static int luasocket_bind(lua_State *L)
 {
 	struct socket *socket = luasocket_checksocket(L, 1);
-	struct sockaddr addr;
+	luasocket_addr_t addr;
 
 	luasocket_checkaddr(L, socket, &addr, 2);
-	luasocket_try(L, kernel_bind, socket, &addr, sizeof(addr));
+	luasocket_try(L, kernel_bind, socket, LUASOCKET_SOCKADDR(addr));
 	return 0;
 }
 
@@ -200,14 +209,14 @@ static int luasocket_accept(lua_State *L)
 static int luasocket_connect(lua_State *L)
 {
 	struct socket *socket = luasocket_checksocket(L, 1);
-	struct sockaddr addr;
+	luasocket_addr_t addr;
 	int nargs = lua_gettop(L);
 	int flags;
 
 	luasocket_checkaddr(L, socket, &addr, 2);
 	flags = luaL_optinteger(L, nargs, 0);
 
-	luasocket_try(L, kernel_connect, socket, &addr, sizeof(addr), flags);
+	luasocket_try(L, kernel_connect, socket, LUASOCKET_SOCKADDR(addr), flags);
 	return 0;
 }