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We shouldn't fork off a utmp helper subprocess when we aren't setuid,

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because (a) under that circumstance we won't be writing to utmp
anyway, and (b) if we aren't setuid, then we won't have created the
pty at the point we fork, so even if our subprocess _could_ have
written to utmp it wouldn't have done it right!

Spotted by valgrind (triggering on the access beyond the end of the
ttyname string in setup_utmp, clueing me in to it having been empty).

[originally from svn r9309]
This commit is contained in:
Simon Tatham 2011-09-19 16:38:23 +00:00
parent 73444adc50
commit f69591412c
1 changed files with 79 additions and 79 deletions
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158
unix/uxpty.c
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@ -167,8 +167,8 @@ static tree234 *ptys_by_pid = NULL;
static Pty single_pty = NULL; static Pty single_pty = NULL;
#ifndef OMIT_UTMP #ifndef OMIT_UTMP
static pid_t pty_utmp_helper_pid; static pid_t pty_utmp_helper_pid = -1;
static int pty_utmp_helper_pipe; static int pty_utmp_helper_pipe = -1;
static int pty_stamped_utmp; static int pty_stamped_utmp;
static struct utmpx utmp_entry; static struct utmpx utmp_entry;
#endif #endif
@ -408,106 +408,106 @@ void pty_pre_init(void)
if (geteuid() != getuid() || getegid() != getgid()) { if (geteuid() != getuid() || getegid() != getgid()) {
pty_open_master(pty); pty_open_master(pty);
}
#ifndef OMIT_UTMP #ifndef OMIT_UTMP
/* /*
* Fork off the utmp helper. * Fork off the utmp helper.
*/ */
if (pipe(pipefd) < 0) { if (pipe(pipefd) < 0) {
perror("pterm: pipe"); perror("pterm: pipe");
exit(1); exit(1);
} }
cloexec(pipefd[0]); cloexec(pipefd[0]);
cloexec(pipefd[1]); cloexec(pipefd[1]);
pid = fork(); pid = fork();
if (pid < 0) { if (pid < 0) {
perror("pterm: fork"); perror("pterm: fork");
exit(1); exit(1);
} else if (pid == 0) { } else if (pid == 0) {
char display[128], buffer[128]; char display[128], buffer[128];
int dlen, ret; int dlen, ret;
close(pipefd[1]); close(pipefd[1]);
/* /*
* Now sit here until we receive a display name from the * Now sit here until we receive a display name from the
* other end of the pipe, and then stamp utmp. Unstamp utmp * other end of the pipe, and then stamp utmp. Unstamp utmp
* again, and exit, when the pipe closes. * again, and exit, when the pipe closes.
*/ */
dlen = 0; dlen = 0;
while (1) { while (1) {
ret = read(pipefd[0], buffer, lenof(buffer)); ret = read(pipefd[0], buffer, lenof(buffer));
if (ret <= 0) { if (ret <= 0) {
cleanup_utmp(); cleanup_utmp();
_exit(0); _exit(0);
} else if (!pty_stamped_utmp) { } else if (!pty_stamped_utmp) {
if (dlen < lenof(display)) if (dlen < lenof(display))
memcpy(display+dlen, buffer, memcpy(display+dlen, buffer,
min(ret, lenof(display)-dlen)); min(ret, lenof(display)-dlen));
if (buffer[ret-1] == '\0') { if (buffer[ret-1] == '\0') {
/* /*
* Now we have a display name. NUL-terminate * Now we have a display name. NUL-terminate
* it, and stamp utmp. * it, and stamp utmp.
*/ */
display[lenof(display)-1] = '\0'; display[lenof(display)-1] = '\0';
/* /*
* Trap as many fatal signals as we can in the * Trap as many fatal signals as we can in the
* hope of having the best possible chance to * hope of having the best possible chance to
* clean up utmp before termination. We are * clean up utmp before termination. We are
* unfortunately unprotected against SIGKILL, * unfortunately unprotected against SIGKILL,
* but that's life. * but that's life.
*/ */
putty_signal(SIGHUP, fatal_sig_handler); putty_signal(SIGHUP, fatal_sig_handler);
putty_signal(SIGINT, fatal_sig_handler); putty_signal(SIGINT, fatal_sig_handler);
putty_signal(SIGQUIT, fatal_sig_handler); putty_signal(SIGQUIT, fatal_sig_handler);
putty_signal(SIGILL, fatal_sig_handler); putty_signal(SIGILL, fatal_sig_handler);
putty_signal(SIGABRT, fatal_sig_handler); putty_signal(SIGABRT, fatal_sig_handler);
putty_signal(SIGFPE, fatal_sig_handler); putty_signal(SIGFPE, fatal_sig_handler);
putty_signal(SIGPIPE, fatal_sig_handler); putty_signal(SIGPIPE, fatal_sig_handler);
putty_signal(SIGALRM, fatal_sig_handler); putty_signal(SIGALRM, fatal_sig_handler);
putty_signal(SIGTERM, fatal_sig_handler); putty_signal(SIGTERM, fatal_sig_handler);
putty_signal(SIGSEGV, fatal_sig_handler); putty_signal(SIGSEGV, fatal_sig_handler);
putty_signal(SIGUSR1, fatal_sig_handler); putty_signal(SIGUSR1, fatal_sig_handler);
putty_signal(SIGUSR2, fatal_sig_handler); putty_signal(SIGUSR2, fatal_sig_handler);
#ifdef SIGBUS #ifdef SIGBUS
putty_signal(SIGBUS, fatal_sig_handler); putty_signal(SIGBUS, fatal_sig_handler);
#endif #endif
#ifdef SIGPOLL #ifdef SIGPOLL
putty_signal(SIGPOLL, fatal_sig_handler); putty_signal(SIGPOLL, fatal_sig_handler);
#endif #endif
#ifdef SIGPROF #ifdef SIGPROF
putty_signal(SIGPROF, fatal_sig_handler); putty_signal(SIGPROF, fatal_sig_handler);
#endif #endif
#ifdef SIGSYS #ifdef SIGSYS
putty_signal(SIGSYS, fatal_sig_handler); putty_signal(SIGSYS, fatal_sig_handler);
#endif #endif
#ifdef SIGTRAP #ifdef SIGTRAP
putty_signal(SIGTRAP, fatal_sig_handler); putty_signal(SIGTRAP, fatal_sig_handler);
#endif #endif
#ifdef SIGVTALRM #ifdef SIGVTALRM
putty_signal(SIGVTALRM, fatal_sig_handler); putty_signal(SIGVTALRM, fatal_sig_handler);
#endif #endif
#ifdef SIGXCPU #ifdef SIGXCPU
putty_signal(SIGXCPU, fatal_sig_handler); putty_signal(SIGXCPU, fatal_sig_handler);
#endif #endif
#ifdef SIGXFSZ #ifdef SIGXFSZ
putty_signal(SIGXFSZ, fatal_sig_handler); putty_signal(SIGXFSZ, fatal_sig_handler);
#endif #endif
#ifdef SIGIO #ifdef SIGIO
putty_signal(SIGIO, fatal_sig_handler); putty_signal(SIGIO, fatal_sig_handler);
#endif
setup_utmp(pty->name, display);
}
}
}
} else {
close(pipefd[0]);
pty_utmp_helper_pid = pid;
pty_utmp_helper_pipe = pipefd[1];
}
#endif #endif
setup_utmp(pty->name, display);
}
}
}
} else {
close(pipefd[0]);
pty_utmp_helper_pid = pid;
pty_utmp_helper_pipe = pipefd[1];
} }
#endif
/* Drop privs. */ /* Drop privs. */
{ {
@ -735,7 +735,7 @@ static const char *pty_init(void *frontend, void **backend_handle, Conf *conf,
if (!conf_get_int(conf, CONF_stamp_utmp)) { if (!conf_get_int(conf, CONF_stamp_utmp)) {
close(pty_utmp_helper_pipe); /* just let the child process die */ close(pty_utmp_helper_pipe); /* just let the child process die */
pty_utmp_helper_pipe = -1; pty_utmp_helper_pipe = -1;
} else { } else if (pty_utmp_helper_pipe >= 0) {
char *location = get_x_display(pty->frontend); char *location = get_x_display(pty->frontend);
int len = strlen(location)+1, pos = 0; /* +1 to include NUL */ int len = strlen(location)+1, pos = 0; /* +1 to include NUL */
while (pos < len) { while (pos < len) {