1.\" Copyright (c) 2010 Maxim Ignatenko <gelraen.ua@gmail.com> 2.\" Copyright (c) 2010 Vadim Goncharov <vadimnuclight@tpu.ru> 3.\" Copyright (c) 2015 Dmitry Vagin <daemon.hammer@ya.ru> 4.\" All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 15.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 16.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 17.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 18.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 19.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 20.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 21.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 22.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 23.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 24.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 25.\" SUCH DAMAGE. 26.\" 27.\" $FreeBSD$ 28.\" 29.Dd November 17, 2015 30.Dt NG_PATCH 4 31.Os 32.Sh NAME 33.Nm ng_patch 34.Nd "trivial mbuf data modifying netgraph node type" 35.Sh SYNOPSIS 36.In netgraph/ng_patch.h 37.Sh DESCRIPTION 38The 39.Nm patch 40node performs data modification of packets passing through it. 41Modifications are restricted to a subset of C language operations 42on unsigned integers of 8, 16, 32 or 64 bit size. 43These are: set to new value (=), addition (+=), subtraction (-=), 44multiplication (*=), division (/=), negation (= -), 45bitwise AND (&=), bitwise OR (|=), bitwise eXclusive OR (^=), 46shift left (<<=), shift right (>>=). 47A negation operation is the one exception: integer is treated as signed 48and second operand (the 49.Va value ) 50is not used. 51If there is more than one modification operation, they are applied 52to packets sequentially in the order they were specified by the user. 53The data payload of a packet is viewed as an array of bytes, with a zero offset 54corresponding to the very first byte of packet headers, and the 55.Va length 56bytes beginning from 57.Va offset 58as a single integer in network byte order. An additional offset can be optionally 59requested at configuration time to account for packet type. 60.Sh HOOKS 61This node type has two hooks: 62.Bl -tag -width ".Va out" 63.It Va in 64Packets received on this hook are modified according to rules specified 65in the configuration and then forwarded to the 66.Ar out 67hook, if it exists. 68Otherwise they are reflected back to the 69.Ar in 70hook. 71.It Va out 72Packets received on this hook are forwarded to the 73.Ar in 74hook without any changes. 75.El 76.Sh CONTROL MESSAGES 77This node type supports the generic control messages, plus the following: 78.Bl -tag -width foo 79.It Dv NGM_PATCH_SETDLT Pq Ic setdlt 80Sets the data link type on the 81.Va in 82hook (to help calculate relative offset). Currently, supported types are 83.Cm DLT_RAW 84(raw IP datagrams , no offset applied, the default) and 85.Cm DLT_EN10MB 86(Ethernet). DLT_ definitions can be found in 87.In net/bpf.h . 88If you want to work on the link layer header you must use no additional offset by specifying 89.Cm DLT_RAW . 90If 91.Cm EN10MB 92is specified, then the optional additional offset will take into account the Ethernet header and a QinQ header if present. 93.It Dv NGM_PATCH_GETDLT Pq Ic getdlt 94This control message returns the data link type of the 95.Va in 96hook. 97.It Dv NGM_PATCH_SETCONFIG Pq Ic setconfig 98This command sets the sequence of modify operations 99that will be applied to incoming data on a hook. 100The following 101.Vt "struct ng_patch_config" 102must be supplied as an argument: 103.Bd -literal -offset 4n 104struct ng_patch_op { 105 uint32_t offset; 106 uint16_t length; /* 1,2,4 or 8 bytes */ 107 uint16_t mode; 108 uint64_t value; 109}; 110/* Patching modes */ 111#define NG_PATCH_MODE_SET 1 112#define NG_PATCH_MODE_ADD 2 113#define NG_PATCH_MODE_SUB 3 114#define NG_PATCH_MODE_MUL 4 115#define NG_PATCH_MODE_DIV 5 116#define NG_PATCH_MODE_NEG 6 117#define NG_PATCH_MODE_AND 7 118#define NG_PATCH_MODE_OR 8 119#define NG_PATCH_MODE_XOR 9 120#define NG_PATCH_MODE_SHL 10 121#define NG_PATCH_MODE_SHR 11 122 123struct ng_patch_config { 124 uint32_t count; 125 uint32_t csum_flags; 126 uint32_t relative_offset; 127 struct ng_patch_op ops[]; 128}; 129.Ed 130.Pp 131The 132.Va csum_flags 133can be set to any combination of CSUM_IP, CSUM_TCP, CSUM_SCTP and CSUM_UDP 134(other values are ignored) for instructing the IP stack to recalculate the 135corresponding checksum before transmitting packet on output interface. 136The 137.Nm 138node does not do any checksum correction by itself. 139.It Dv NGM_PATCH_GETCONFIG Pq Ic getconfig 140This control message returns the current set of modify operations, 141in the form of a 142.Vt "struct ng_patch_config" . 143.It Dv NGM_PATCH_GET_STATS Pq Ic getstats 144Returns the node's statistics as a 145.Vt "struct ng_patch_stats" . 146.It Dv NGM_PATCH_CLR_STATS Pq Ic clrstats 147Clears the node's statistics. 148.It Dv NGM_PATCH_GETCLR_STATS Pq Ic getclrstats 149This command is identical to 150.Dv NGM_PATCH_GET_STATS , 151except that the statistics are also atomically cleared. 152.El 153.Sh SHUTDOWN 154This node shuts down upon receipt of a 155.Dv NGM_SHUTDOWN 156control message, or when all hooks have been disconnected. 157.Sh EXAMPLES 158This 159.Nm 160node was designed to modify TTL and TOS/DSCP fields in IP packets. 161As an example, 162suppose you have two adjacent simplex links to a remote network 163(e.g.\& satellite), so that the packets expiring in between 164will generate unwanted ICMP-replies which have to go forth, not back. 165Thus you need to raise TTL of every packet entering link by 2 166to ensure the TTL will not reach zero there. 167To achieve this you can set an 168.Xr ipfw 8 169rule to use the 170.Cm netgraph 171action to inject packets which are going to the simplex link into the patch node, by using the 172following 173.Xr ngctl 8 174script: 175.Bd -literal -offset 4n 176/usr/sbin/ngctl -f- <<-SEQ 177 mkpeer ipfw: patch 200 in 178 name ipfw:200 ttl_add 179 msg ttl_add: setconfig { count=1 csum_flags=1 ops=[ \e 180 { mode=2 value=3 length=1 offset=8 } ] } 181SEQ 182/sbin/ipfw add 150 netgraph 200 ip from any to simplex.remote.net 183.Ed 184.Pp 185Here the 186.Dq Li ttl_add 187node of type 188.Nm 189is configured to add (mode 190.Dv NG_PATCH_MODE_ADD ) 191a 192.Va value 193of 3 to a one-byte TTL field, which is 9th byte of IP packet header. 194.Pp 195Another example would be two consecutive modifications of packet TOS 196field: say, you need to clear the 197.Dv IPTOS_THROUGHPUT 198bit and set the 199.Dv IPTOS_MINCOST 200bit. 201So you do: 202.Bd -literal -offset 4n 203/usr/sbin/ngctl -f- <<-SEQ 204 mkpeer ipfw: patch 300 in 205 name ipfw:300 tos_chg 206 msg tos_chg: setconfig { count=2 csum_flags=1 ops=[ \e 207 { mode=7 value=0xf7 length=1 offset=1 } \e 208 { mode=8 value=0x02 length=1 offset=1 } ] } 209SEQ 210/sbin/ipfw add 160 netgraph 300 ip from any to any not dst-port 80 211.Ed 212.Pp 213This first does 214.Dv NG_PATCH_MODE_AND 215clearing the fourth bit and then 216.Dv NG_PATCH_MODE_OR 217setting the third bit. 218.Pp 219In both examples the 220.Va csum_flags 221field indicates that IP checksum (but not TCP or UDP checksum) should be 222recalculated before transmit. 223.Pp 224Note: one should ensure that packets are returned to ipfw after processing 225inside 226.Xr netgraph 4 , 227by setting appropriate 228.Xr sysctl 8 229variable: 230.Bd -literal -offset 4n 231sysctl net.inet.ip.fw.one_pass=0 232.Ed 233.Sh SEE ALSO 234.Xr netgraph 4 , 235.Xr ng_ipfw 4 , 236.Xr ngctl 8 237.Sh HISTORY 238The 239.Nm 240node type was implemented in 241.Fx 8.1 . 242.Sh AUTHORS 243.An "Maxim Ignatenko" Aq gelraen.ua@gmail.com . 244.Pp 245Relative offset code by 246.An "DMitry Vagin" 247.Pp 248This manual page was written by 249.An "Vadim Goncharov" Aq vadimnuclight@tpu.ru . 250.Sh BUGS 251The node blindly tries to apply every patching operation to each packet 252(except those which offset if greater than length of the packet), 253so be sure that you supply only the right packets to it (e.g. changing 254bytes in the ARP packets meant to be in IP header could corrupt 255them and make your machine unreachable from the network). 256.Pp 257.Em !!! WARNING !!! 258.Pp 259The output path of the IP stack assumes correct fields and lengths in the 260packets - changing them by to incorrect values can cause 261unpredictable results including kernel panics. 262