1 /*-
2 * SPDX-License-Identifier: BSD-2-Clause
3 *
4 * Copyright (c) 2023 Klara, Inc.
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 #include <sys/cdefs.h>
28
29 #include <err.h>
30 #include <errno.h>
31 #include <fcntl.h>
32 #include <limits.h>
33 #include <stdlib.h>
34 #include <string.h>
35 #include <stdio.h>
36 #include <unistd.h>
37
38 static int
exec_shortargs(char * argv[])39 exec_shortargs(char *argv[])
40 {
41 char *flag_arg = argv[2];
42 char *sentinel = argv[3];
43 char * nargv[] = { argv[0], __DECONST(char *, "--spin"), flag_arg,
44 sentinel, NULL };
45 char * const nenvp[] = { NULL };
46
47 execve(argv[0], nargv, nenvp);
48 err(1, "execve");
49 }
50
51 static int
exec_largeargs(char * argv[])52 exec_largeargs(char *argv[])
53 {
54 char *flag_arg = argv[2];
55 char *sentinel = argv[3];
56 /*
57 * Account for each argument and their NUL terminator, as well as an
58 * extra NUL terminator.
59 */
60 size_t bufsz = ARG_MAX -
61 ((strlen(argv[0]) + 1) + sizeof("--spin") + (strlen(flag_arg) + 1) +
62 (strlen(sentinel) + 1) + 1);
63 char *s = NULL;
64 char * nargv[] = { argv[0], __DECONST(char *, "--spin"), flag_arg, NULL,
65 sentinel, NULL };
66 char * const nenvp[] = { NULL };
67
68 /*
69 * Our heuristic may or may not be accurate, we'll keep trying with
70 * smaller argument sizes as needed until we stop getting E2BIG.
71 */
72 do {
73 if (s == NULL)
74 s = malloc(bufsz + 1);
75 else
76 s = realloc(s, bufsz + 1);
77 if (s == NULL)
78 abort();
79 memset(s, 'x', bufsz);
80 s[bufsz] = '\0';
81 nargv[3] = s;
82
83 execve(argv[0], nargv, nenvp);
84 bufsz--;
85 } while (errno == E2BIG);
86 err(1, "execve");
87 }
88
89 int
main(int argc,char * argv[])90 main(int argc, char *argv[])
91 {
92
93 if (argc > 1 && strcmp(argv[1], "--spin") == 0) {
94 int fd;
95
96 if (argc < 4) {
97 fprintf(stderr, "usage: %s --spin flagfile ...\n", argv[0]);
98 return (1);
99 }
100
101 fd = open(argv[2], O_RDWR | O_CREAT, 0755);
102 if (fd < 0)
103 err(1, "%s", argv[2]);
104 close(fd);
105
106 for (;;) {
107 sleep(1);
108 }
109
110 return (1);
111 }
112
113 if (argc != 4) {
114 fprintf(stderr, "usage: %s [--short | --long] flagfile sentinel\n",
115 argv[0]);
116 return (1);
117 }
118
119 if (strcmp(argv[1], "--short") == 0)
120 exec_shortargs(argv);
121 else
122 exec_largeargs(argv);
123 }
124