1 /* $NetBSD: panic_string.c,v 1.3 2021/10/21 13:21:55 andvar Exp $ */
2
3 /*-
4 * Copyright (c) 2018 The NetBSD Foundation, Inc.
5 * All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
17 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
18 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
19 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
20 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
21 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
22 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
23 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
24 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
25 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
26 * POSSIBILITY OF SUCH DAMAGE.
27 */
28
29
30 #include <sys/cdefs.h>
31 __KERNEL_RCSID(0, "$NetBSD: panic_string.c,v 1.3 2021/10/21 13:21:55 andvar Exp $");
32
33 #include <sys/param.h>
34 #include <sys/types.h>
35 #include <sys/conf.h>
36 #include <sys/device.h>
37 #include <sys/filedesc.h>
38 #include <sys/kernel.h>
39 #include <sys/kmem.h>
40 #include <sys/lwp.h>
41 #include <sys/module.h>
42 #include <sys/vfs_syscalls.h>
43
44 /*
45 * Create a device /dev/panic from which you can read sequential
46 * user input.
47 *
48 * To use this device you need to do:
49 * mknod /dev/panic c 351 0
50 *
51 * To write to the device you might need:
52 * chmod 666 /dev/panic
53 *
54 * Commentary:
55 * This module manages the device /dev/panic,
56 * transfers a string from userspace to kernel space
57 * and calls kernel panic with the passed string.
58 *
59 * echo 'string' > /dev/panic
60 * will do the trick after loading the module.
61 */
62
63 dev_type_open(panic_string_open);
64 dev_type_close(panic_string_close);
65 dev_type_write(panic_string_write);
66
67 static struct cdevsw panic_string_cdevsw = {
68 .d_open = panic_string_open,
69 .d_close = panic_string_close,
70 .d_read = noread,
71 .d_write = panic_string_write,
72 .d_ioctl = noioctl,
73 .d_stop = nostop,
74 .d_tty = notty,
75 .d_poll = nopoll,
76 .d_mmap = nommap,
77 .d_kqfilter = nokqfilter,
78 .d_discard = nodiscard,
79 .d_flag = D_OTHER
80 };
81
82 static struct panic_string_softc {
83 int refcnt;
84 } sc;
85
86 /*
87 * A function similar to strnlen + isprint
88 *
89 * Detect length of the printable and non-whitespace string in the buffer.
90 * A string is accepted if it contains any non-space character.
91 */
92
93 static size_t
printable_length(const char * str,size_t len)94 printable_length(const char *str, size_t len)
95 {
96 size_t n;
97 bool accepted;
98
99 n = 0;
100 accepted = false;
101
102 while (len > n) {
103 if (str[n] >= 0x20 && str[n] <= 0x7e) {
104 if (str[n] != 0x20 /* space */)
105 accepted = true;
106 n++;
107 } else
108 break;
109 }
110
111 if (accepted)
112 return n;
113 else
114 return 0;
115 }
116
117 int
panic_string_open(dev_t self __unused,int flag __unused,int mod __unused,struct lwp * l)118 panic_string_open(dev_t self __unused, int flag __unused, int mod __unused, struct lwp *l)
119 {
120
121 /* Make sure the device is opened once at a time */
122 if (sc.refcnt > 0)
123 return EBUSY;
124
125 ++sc.refcnt;
126
127 return 0;
128 }
129
130 int
panic_string_close(dev_t self __unused,int flag __unused,int mod __unused,struct lwp * l __unused)131 panic_string_close(dev_t self __unused, int flag __unused, int mod __unused, struct lwp *l __unused)
132 {
133
134 --sc.refcnt;
135 return 0;
136 }
137
138 int
panic_string_write(dev_t self,struct uio * uio,int flags)139 panic_string_write(dev_t self, struct uio *uio, int flags)
140 {
141 size_t len, printlen;
142 char *buffer;
143
144 /* Buffer length */
145 len = uio->uio_iov->iov_len;
146
147 /* Allocate a local buffer to store the string */
148 buffer = (char *)kmem_alloc(len, KM_SLEEP);
149
150 /* Move the string from user to kernel space and store it locally */
151 uiomove(buffer, len, uio);
152
153 printlen = printable_length(buffer, len);
154
155 if (printlen > 0) {
156 /* Flushing disk changes */
157 do_sys_sync(curlwp);
158
159 panic("panic string: %.*s\n", (int)printlen, buffer);
160 // printf("panic string: %.*s\n", (int)printlen, buffer);
161
162 /* NOTREACHED */
163 }
164
165 kmem_free(buffer, len);
166 return 0;
167 }
168
169 MODULE(MODULE_CLASS_MISC, panic_string, NULL);
170
171 static int
panic_string_modcmd(modcmd_t cmd,void * arg __unused)172 panic_string_modcmd(modcmd_t cmd, void *arg __unused)
173 {
174 /* The major should be verified and changed if needed to avoid
175 * conflicts with other devices. */
176 int cmajor = 351, bmajor = -1;
177
178 switch (cmd) {
179 case MODULE_CMD_INIT:
180 printf("Panic String module loaded.\n");
181 if (devsw_attach("panic", NULL, &bmajor, &panic_string_cdevsw,
182 &cmajor))
183 return ENXIO;
184 return 0;
185
186 case MODULE_CMD_FINI:
187 printf("Panic String module unloaded.\n");
188 if (sc.refcnt > 0)
189 return EBUSY;
190
191 devsw_detach(NULL, &panic_string_cdevsw);
192 return 0;
193 default:
194 return ENOTTY;
195 }
196 }
197