89 lines
2.1 KiB
C
89 lines
2.1 KiB
C
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/* This file is part of the sample code and exercises
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* used by the class "Advanced Programming in the UNIX
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* Environment" taught by Jan Schaumann
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* <jschauma@netmeister.org> at Stevens Institute of
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* Technology.
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*
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* This file is in the public domain.
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*
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* You don't have to, but if you feel like
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* acknowledging where you got this code, you may
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* reference me by name, email address, or point
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* people to the course website:
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* https://stevens.netmeister.org/631/
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*/
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/* This program illustrates the risk of calling non-re-entrant functions
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* in your signal handler. Depending on the platform, the results of
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* running this program may differ, but you will see a number of possible
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* results:
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* - user not found: you accidentally 'skipped' over the entry you were
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* looking for
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* - return value corrupted: you got back a different struct passwd then
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* the one you requested
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* - memory fault: FUBAR
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*/
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#include <err.h>
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#include <errno.h>
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#include <pwd.h>
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#include <signal.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <unistd.h>
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#ifndef USER
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#define USER "jschauma"
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#endif
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static void
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my_alarm(int signo)
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{
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struct passwd *rootptr;
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(void)signo;
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(void)write(STDOUT_FILENO, "SIGALRM\n", 8);
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for (int i=0; i<3; i++) {
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if ((rootptr = getpwnam("root")) == NULL) {
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(void)write(STDERR_FILENO, "no 'root' found!\n", 17);
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exit(EXIT_FAILURE);
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/* NOTREACHED */
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}
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}
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if (alarm(1) == (unsigned int)-1) {
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err(EXIT_FAILURE, "alarm");
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/* NOTREACHED */
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}
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}
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int
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main(void) {
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struct passwd *ptr;
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if (signal(SIGALRM, my_alarm) == SIG_ERR) {
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fprintf(stderr, "Unable to establish signal handler: %s\n", strerror(errno));
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exit(EXIT_FAILURE);
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/* NOTREACHED */
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}
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if (alarm(1) == (unsigned int)-1) {
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err(EXIT_FAILURE, "alarm");
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/* NOTREACHED */
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}
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for ( ; ; ) {
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if ((ptr = getpwnam(USER)) == NULL) {
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fprintf(stderr, "user %s not found!\n", USER);
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exit(EXIT_FAILURE);
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/* NOTREACHED */
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}
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if (strcmp(ptr->pw_name, USER) != 0) {
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fprintf(stderr, "return value corrupted: pw_name = %s\n",
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ptr->pw_name);
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abort();
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/* NOTREACHED */
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}
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}
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}
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