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rc: avoid calling free inside SIGCHLD handler

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`free` is not async-signal-safe and calling it inside a signal handler
can have bad effects, as reported in the musl ML:
https://www.openwall.com/lists/musl/2023/01/23/1

the solution:

- keep track of weather remove_pid() is being called from inside a
  signal handler or not.
- if it's inside a signal handler then DO NOT call free - instead put
  that pointer into a "to be freed later" list.
- if it's not inside a signal handler then take the "to be freed later"
  list and free anything in it.

Bug: https://github.com/OpenRC/openrc/issues/589
Reported-by: Dominique MARTINET <dominique.martinet@atmark-techno.com>
This commit is contained in:
NRK 2023-01-28 18:38:52 +06:00 committed by William Hubbs
parent 910e3e2a0e
commit bbd3acfc67
1 changed files with 27 additions and 11 deletions
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30
src/openrc/rc.c
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@ -87,6 +87,7 @@ static RC_HOOK hook_out;
struct termios *termios_orig = NULL; struct termios *termios_orig = NULL;
RC_PIDLIST service_pids; RC_PIDLIST service_pids;
RC_PIDLIST free_these_pids;
static void static void
clean_failed(void) clean_failed(void)
@ -145,6 +146,12 @@ cleanup(void)
p1 = p2; p1 = p2;
} }
for (p1 = LIST_FIRST(&free_these_pids); p1; /* no-op */) {
p2 = LIST_NEXT(p1, entries);
free(p1);
p1 = p2;
}
rc_stringlist_free(main_hotplugged_services); rc_stringlist_free(main_hotplugged_services);
rc_stringlist_free(main_stop_services); rc_stringlist_free(main_stop_services);
rc_stringlist_free(main_start_services); rc_stringlist_free(main_start_services);
@ -350,15 +357,23 @@ add_pid(pid_t pid)
} }
static void static void
remove_pid(pid_t pid) remove_pid(pid_t pid, bool inside_signal)
{ {
RC_PID *p; RC_PID *p, *tmp;
LIST_FOREACH(p, &service_pids, entries) LIST_FOREACH(p, &service_pids, entries) {
if (p->pid == pid) { if (p->pid == pid) {
LIST_REMOVE(p, entries);
LIST_INSERT_HEAD(&free_these_pids, p, entries);
break;
}
}
/* only call free if we're not inside a signal handler */
if (!inside_signal) {
LIST_FOREACH_SAFE(p, &free_these_pids, entries, tmp) {
LIST_REMOVE(p, entries); LIST_REMOVE(p, entries);
free(p); free(p);
return; }
} }
} }
@ -397,7 +412,7 @@ handle_signal(int sig)
/* Remove that pid from our list */ /* Remove that pid from our list */
if (pid > 0) if (pid > 0)
remove_pid(pid); remove_pid(pid, true);
break; break;
case SIGWINCH: case SIGWINCH:
@ -606,7 +621,7 @@ stop:
add_pid(pid); add_pid(pid);
if (!parallel) { if (!parallel) {
rc_waitpid(pid); rc_waitpid(pid);
remove_pid(pid); remove_pid(pid, false);
} }
} }
} }
@ -672,7 +687,7 @@ do_start_services(const RC_STRINGLIST *start_services, bool parallel)
add_pid(pid); add_pid(pid);
if (!parallel) { if (!parallel) {
rc_waitpid(pid); rc_waitpid(pid);
remove_pid(pid); remove_pid(pid, false);
} }
} }
} }
@ -745,6 +760,7 @@ int main(int argc, char **argv)
applet = basename_c(argv[0]); applet = basename_c(argv[0]);
LIST_INIT(&service_pids); LIST_INIT(&service_pids);
LIST_INIT(&free_these_pids);
atexit(cleanup); atexit(cleanup);
if (!applet) if (!applet)
eerrorx("arguments required"); eerrorx("arguments required");