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Fix race in pselect replacement code. 

On the second and subsequent calls to pselect the notify_pipe was not
added to the select readset, opening up a race that om G. Christensen
discovered on multiprocessor Solaris <=9 systems.

Also reinitialize notify_pipe if the pid changes.  This will prevent a
parent and child from using the same FD, although this is not an issue
in the current structure it might be in future.
This commit is contained in:
Darren Tucker 2021-08-20 08:30:42 +10:00
parent 464ba22f1e
commit 10e45654cf
1 changed files with 19 additions and 4 deletions
openbsd-compat
bsd-pselect.c

23
openbsd-compat/bsd-pselect.c
View File

@ -73,6 +73,7 @@ notify_setup_fd(int *fd)
* we write to this pipe if a SIGCHLD is caught in order to avoid
* the race between select() and child_terminated
*/
static pid_t notify_pid;
static int notify_pipe[2];
static void
notify_setup(void)
@ -81,6 +82,15 @@ notify_setup(void)
if (initialized)
return;
if (notify_pid == 0)
debug3_f("initializing");
else {
debug3_f("pid changed, reinitializing");
if (notify_pipe[0] != -1)
close(notify_pipe[0]);
if (notify_pipe[1] != -1)
close(notify_pipe[1]);
}
if (pipe(notify_pipe) == -1) {
error("pipe(notify_pipe) failed %s", strerror(errno));
} else if (notify_setup_fd(&notify_pipe[0]) == -1 ||
@ -91,6 +101,9 @@ notify_setup(void)
} else {
set_nonblock(notify_pipe[0]);
set_nonblock(notify_pipe[1]);
notify_pid = getpid();
debug3_f("pid %d saved %d pipe0 %d pipe1 %d", getpid(),
notify_pid, notify_pipe[0], notify_pipe[1]);
initialized = 1;
return;
}
@ -159,15 +172,16 @@ pselect(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
if (sig == SIGKILL || sig == SIGSTOP || sigismember(mask, sig))
continue;
if (sigaction(sig, NULL, &sa) == 0 &&
sa.sa_handler != SIG_IGN && sa.sa_handler != SIG_DFL &&
sa.sa_handler != sig_handler) {
sa.sa_handler != SIG_IGN && sa.sa_handler != SIG_DFL) {
unmasked = 1;
if (sa.sa_handler == sig_handler)
continue;
sa.sa_handler = sig_handler;
if (sigaction(sig, &sa, &osa) == 0) {
debug3_f("installing signal handler for %s, "
"previous %p", strsignal(sig),
osa.sa_handler);
saved_sighandler[sig] = osa.sa_handler;
unmasked = 1;
}
}
}
@ -183,7 +197,8 @@ pselect(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
saved_errno = errno;
sigprocmask(SIG_SETMASK, &osig, NULL);
notify_done(readfds);
if (unmasked)
notify_done(readfds);
errno = saved_errno;
return ret;
}