1 /*
2 * a race in pid generation that causes pids to be reused immediately
3 *
4 * From the mainline commit 5fdee8c4a5e1800489ce61963208f8cc55e42ea1:
5 *
6 * A program that repeatedly forks and waits is susceptible to having
7 * the same pid repeated, especially when it competes with another
8 * instance of the same program. This is really bad for bash
9 * implementation. Furthermore, many shell scripts assume that pid
10 * numbers will not be used for some length of time.
11 *
12 * Race Description:
13 *
14 * A B
15 *
16 * // pid == offset == n // pid == offset == n + 1
17 * test_and_set_bit(offset, map->page)
18 * test_and_set_bit(offset, map->page);
19 * pid_ns->last_pid = pid;
20 * pid_ns->last_pid = pid;
21 * // pid == n + 1 is freed (wait())
22 *
23 * // Next fork()...
24 * last = pid_ns->last_pid; // == n
25 * pid = last + 1;
26 *
27 * Copyright (C) 2010 Red Hat, Inc.
28 * This program is free software; you can redistribute it and/or
29 * modify it under the terms of version 2 of the GNU General Public
30 * License as published by the Free Software Foundation.
31 *
32 * This program is distributed in the hope that it would be useful,
33 * but WITHOUT ANY WARRANTY; without even the implied warranty of
34 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
35 *
36 * Further, this software is distributed without any warranty that it
37 * is free of the rightful claim of any third person regarding
38 * infringement or the like. Any license provided herein, whether
39 * implied or otherwise, applies only to this software file. Patent
40 * licenses, if any, provided herein do not apply to combinations of
41 * this program with other software, or any other product whatsoever.
42 *
43 * You should have received a copy of the GNU General Public License
44 * along with this program; if not, write the Free Software
45 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
46 * 02110-1301, USA.
47 */
48
49 #include <sys/types.h>
50 #include <sys/stat.h>
51 #include <sys/wait.h>
52 #include <fcntl.h>
53 #include <errno.h>
54 #include <unistd.h>
55 #include <stdio.h>
56 #include <stdlib.h>
57 #include "test.h"
58
59 char *TCID = "fork13";
60 int TST_TOTAL = 1;
61
62 static unsigned long pid_max;
63
64 #define PID_MAX_PATH "/proc/sys/kernel/pid_max"
65 #define PID_MAX 32768
66 #define RETURN 256
67
68 static void setup(void);
69 static int pid_distance(pid_t first, pid_t second);
70 static void cleanup(void);
71 static void check(void);
72
main(int argc,char * argv[])73 int main(int argc, char *argv[])
74 {
75 tst_parse_opts(argc, argv, NULL, NULL);
76 setup();
77 check();
78 cleanup();
79 tst_exit();
80 }
81
check(void)82 static void check(void)
83 {
84 long lc;
85 pid_t last_pid = 0;
86 pid_t pid;
87 int child_exit_code, distance, reaped, status;
88
89 for (lc = 0; TEST_LOOPING(lc); lc++) {
90 tst_count = 0;
91 child_exit_code = lc % RETURN;
92 switch (pid = fork()) {
93 case -1:
94 tst_brkm(TBROK | TERRNO, cleanup, "fork");
95 case 0:
96 exit(child_exit_code);
97 default:
98 if (lc > 0) {
99 distance = pid_distance(last_pid, pid);
100 if (distance == 0) {
101 tst_resm(TFAIL,
102 "Unexpected pid sequence: "
103 "previous fork: pid=%d, "
104 "current fork: pid=%d for "
105 "iteration=%ld.", last_pid,
106 pid, lc);
107 return;
108 }
109 }
110 last_pid = pid;
111
112 reaped = waitpid(pid, &status, 0);
113 if (reaped != pid) {
114 tst_resm(TFAIL,
115 "Wait return value: expected pid=%d, "
116 "got %d, iteration %ld.", pid, reaped,
117 lc);
118 return;
119 } else if (WEXITSTATUS(status) != child_exit_code) {
120 tst_resm(TFAIL, "Unexpected exit status %x, "
121 "iteration %ld.", WEXITSTATUS(status),
122 lc);
123 return;
124 }
125 }
126 }
127 tst_resm(TPASS, "%ld pids forked, all passed", lc);
128 }
129
setup(void)130 static void setup(void)
131 {
132 tst_require_root();
133
134 tst_sig(FORK, DEF_HANDLER, cleanup);
135 TEST_PAUSE;
136
137 /* Backup pid_max value. */
138 SAFE_FILE_SCANF(NULL, PID_MAX_PATH, "%lu", &pid_max);
139
140 SAFE_FILE_PRINTF(NULL, PID_MAX_PATH, "%d", PID_MAX);
141 }
142
cleanup(void)143 static void cleanup(void)
144 {
145 /* Restore pid_max value. */
146 FILE_PRINTF(PID_MAX_PATH, "%lu", pid_max);
147 }
148
149 /* The distance mod PIDMAX between two pids, where the first pid is
150 expected to be smaller than the second. */
pid_distance(pid_t first,pid_t second)151 static int pid_distance(pid_t first, pid_t second)
152 {
153 return (second + PID_MAX - first) % PID_MAX;
154 }
155