1 | #include <machine/rtems-bsd-kernel-space.h> |
---|
2 | |
---|
3 | |
---|
4 | /*- |
---|
5 | * Copyright (c) 2008 Michael J. Silbersack. |
---|
6 | * All rights reserved. |
---|
7 | * |
---|
8 | * Redistribution and use in source and binary forms, with or without |
---|
9 | * modification, are permitted provided that the following conditions |
---|
10 | * are met: |
---|
11 | * 1. Redistributions of source code must retain the above copyright |
---|
12 | * notice unmodified, this list of conditions, and the following |
---|
13 | * disclaimer. |
---|
14 | * 2. Redistributions in binary form must reproduce the above copyright |
---|
15 | * notice, this list of conditions and the following disclaimer in the |
---|
16 | * documentation and/or other materials provided with the distribution. |
---|
17 | * |
---|
18 | * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR |
---|
19 | * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES |
---|
20 | * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. |
---|
21 | * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, |
---|
22 | * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT |
---|
23 | * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
---|
24 | * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
---|
25 | * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
---|
26 | * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF |
---|
27 | * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
---|
28 | */ |
---|
29 | |
---|
30 | #include <sys/cdefs.h> |
---|
31 | __FBSDID("$FreeBSD$"); |
---|
32 | |
---|
33 | /* |
---|
34 | * IP ID generation is a fascinating topic. |
---|
35 | * |
---|
36 | * In order to avoid ID collisions during packet reassembly, common sense |
---|
37 | * dictates that the period between reuse of IDs be as large as possible. |
---|
38 | * This leads to the classic implementation of a system-wide counter, thereby |
---|
39 | * ensuring that IDs repeat only once every 2^16 packets. |
---|
40 | * |
---|
41 | * Subsequent security researchers have pointed out that using a global |
---|
42 | * counter makes ID values predictable. This predictability allows traffic |
---|
43 | * analysis, idle scanning, and even packet injection in specific cases. |
---|
44 | * These results suggest that IP IDs should be as random as possible. |
---|
45 | * |
---|
46 | * The "searchable queues" algorithm used in this IP ID implementation was |
---|
47 | * proposed by Amit Klein. It is a compromise between the above two |
---|
48 | * viewpoints that has provable behavior that can be tuned to the user's |
---|
49 | * requirements. |
---|
50 | * |
---|
51 | * The basic concept is that we supplement a standard random number generator |
---|
52 | * with a queue of the last L IDs that we have handed out to ensure that all |
---|
53 | * IDs have a period of at least L. |
---|
54 | * |
---|
55 | * To efficiently implement this idea, we keep two data structures: a |
---|
56 | * circular array of IDs of size L and a bitstring of 65536 bits. |
---|
57 | * |
---|
58 | * To start, we ask the RNG for a new ID. A quick index into the bitstring |
---|
59 | * is used to determine if this is a recently used value. The process is |
---|
60 | * repeated until a value is returned that is not in the bitstring. |
---|
61 | * |
---|
62 | * Having found a usable ID, we remove the ID stored at the current position |
---|
63 | * in the queue from the bitstring and replace it with our new ID. Our new |
---|
64 | * ID is then added to the bitstring and the queue pointer is incremented. |
---|
65 | * |
---|
66 | * The lower limit of 512 was chosen because there doesn't seem to be much |
---|
67 | * point to having a smaller value. The upper limit of 32768 was chosen for |
---|
68 | * two reasons. First, every step above 32768 decreases the entropy. Taken |
---|
69 | * to an extreme, 65533 would offer 1 bit of entropy. Second, the number of |
---|
70 | * attempts it takes the algorithm to find an unused ID drastically |
---|
71 | * increases, killing performance. The default value of 8192 was chosen |
---|
72 | * because it provides a good tradeoff between randomness and non-repetition. |
---|
73 | * |
---|
74 | * With L=8192, the queue will use 16K of memory. The bitstring always |
---|
75 | * uses 8K of memory. No memory is allocated until the use of random ids is |
---|
76 | * enabled. |
---|
77 | */ |
---|
78 | |
---|
79 | #include <sys/types.h> |
---|
80 | #include <sys/malloc.h> |
---|
81 | #include <rtems/bsd/sys/param.h> |
---|
82 | #include <sys/time.h> |
---|
83 | #include <sys/kernel.h> |
---|
84 | #include <sys/libkern.h> |
---|
85 | #include <rtems/bsd/sys/lock.h> |
---|
86 | #include <sys/mutex.h> |
---|
87 | #include <sys/random.h> |
---|
88 | #include <sys/systm.h> |
---|
89 | #include <sys/sysctl.h> |
---|
90 | #include <netinet/in.h> |
---|
91 | #include <netinet/ip_var.h> |
---|
92 | #include <sys/bitstring.h> |
---|
93 | |
---|
94 | static MALLOC_DEFINE(M_IPID, "ipid", "randomized ip id state"); |
---|
95 | |
---|
96 | static u_int16_t *id_array = NULL; |
---|
97 | static bitstr_t *id_bits = NULL; |
---|
98 | static int array_ptr = 0; |
---|
99 | static int array_size = 8192; |
---|
100 | static int random_id_collisions = 0; |
---|
101 | static int random_id_total = 0; |
---|
102 | static struct mtx ip_id_mtx; |
---|
103 | |
---|
104 | static void ip_initid(void); |
---|
105 | static int sysctl_ip_id_change(SYSCTL_HANDLER_ARGS); |
---|
106 | |
---|
107 | MTX_SYSINIT(ip_id_mtx, &ip_id_mtx, "ip_id_mtx", MTX_DEF); |
---|
108 | |
---|
109 | SYSCTL_DECL(_net_inet_ip); |
---|
110 | SYSCTL_PROC(_net_inet_ip, OID_AUTO, random_id_period, CTLTYPE_INT|CTLFLAG_RW, |
---|
111 | &array_size, 0, sysctl_ip_id_change, "IU", "IP ID Array size"); |
---|
112 | SYSCTL_INT(_net_inet_ip, OID_AUTO, random_id_collisions, CTLFLAG_RD, |
---|
113 | &random_id_collisions, 0, "Count of IP ID collisions"); |
---|
114 | SYSCTL_INT(_net_inet_ip, OID_AUTO, random_id_total, CTLFLAG_RD, |
---|
115 | &random_id_total, 0, "Count of IP IDs created"); |
---|
116 | |
---|
117 | static int |
---|
118 | sysctl_ip_id_change(SYSCTL_HANDLER_ARGS) |
---|
119 | { |
---|
120 | int error, new; |
---|
121 | |
---|
122 | new = array_size; |
---|
123 | error = sysctl_handle_int(oidp, &new, 0, req); |
---|
124 | if (error == 0 && req->newptr) { |
---|
125 | if (new >= 512 && new <= 32768) { |
---|
126 | mtx_lock(&ip_id_mtx); |
---|
127 | array_size = new; |
---|
128 | ip_initid(); |
---|
129 | mtx_unlock(&ip_id_mtx); |
---|
130 | } else |
---|
131 | error = EINVAL; |
---|
132 | } |
---|
133 | return (error); |
---|
134 | } |
---|
135 | |
---|
136 | /* |
---|
137 | * ip_initid() runs with a mutex held and may execute in a network context. |
---|
138 | * As a result, it uses M_NOWAIT. Ideally, we would always do this |
---|
139 | * allocation from the sysctl contact and have it be an invariant that if |
---|
140 | * this random ID allocation mode is selected, the buffers are present. This |
---|
141 | * would also avoid potential network context failures of IP ID generation. |
---|
142 | */ |
---|
143 | static void |
---|
144 | ip_initid(void) |
---|
145 | { |
---|
146 | |
---|
147 | mtx_assert(&ip_id_mtx, MA_OWNED); |
---|
148 | |
---|
149 | if (id_array != NULL) { |
---|
150 | free(id_array, M_IPID); |
---|
151 | free(id_bits, M_IPID); |
---|
152 | } |
---|
153 | random_id_collisions = 0; |
---|
154 | random_id_total = 0; |
---|
155 | array_ptr = 0; |
---|
156 | id_array = (u_int16_t *) malloc(array_size * sizeof(u_int16_t), |
---|
157 | M_IPID, M_NOWAIT | M_ZERO); |
---|
158 | id_bits = (bitstr_t *) malloc(bitstr_size(65536), M_IPID, |
---|
159 | M_NOWAIT | M_ZERO); |
---|
160 | if (id_array == NULL || id_bits == NULL) { |
---|
161 | /* Neither or both. */ |
---|
162 | if (id_array != NULL) { |
---|
163 | free(id_array, M_IPID); |
---|
164 | id_array = NULL; |
---|
165 | } |
---|
166 | if (id_bits != NULL) { |
---|
167 | free(id_bits, M_IPID); |
---|
168 | id_bits = NULL; |
---|
169 | } |
---|
170 | } |
---|
171 | } |
---|
172 | |
---|
173 | u_int16_t |
---|
174 | ip_randomid(void) |
---|
175 | { |
---|
176 | u_int16_t new_id; |
---|
177 | |
---|
178 | mtx_lock(&ip_id_mtx); |
---|
179 | if (id_array == NULL) |
---|
180 | ip_initid(); |
---|
181 | |
---|
182 | /* |
---|
183 | * Fail gracefully; return a fixed id if memory allocation failed; |
---|
184 | * ideally we wouldn't do allocation in this context in order to |
---|
185 | * avoid the possibility of this failure mode. |
---|
186 | */ |
---|
187 | if (id_array == NULL) { |
---|
188 | mtx_unlock(&ip_id_mtx); |
---|
189 | return (1); |
---|
190 | } |
---|
191 | |
---|
192 | /* |
---|
193 | * To avoid a conflict with the zeros that the array is initially |
---|
194 | * filled with, we never hand out an id of zero. |
---|
195 | */ |
---|
196 | new_id = 0; |
---|
197 | do { |
---|
198 | if (new_id != 0) |
---|
199 | random_id_collisions++; |
---|
200 | arc4rand(&new_id, sizeof(new_id), 0); |
---|
201 | } while (bit_test(id_bits, new_id) || new_id == 0); |
---|
202 | bit_clear(id_bits, id_array[array_ptr]); |
---|
203 | bit_set(id_bits, new_id); |
---|
204 | id_array[array_ptr] = new_id; |
---|
205 | array_ptr++; |
---|
206 | if (array_ptr == array_size) |
---|
207 | array_ptr = 0; |
---|
208 | random_id_total++; |
---|
209 | mtx_unlock(&ip_id_mtx); |
---|
210 | return (new_id); |
---|
211 | } |
---|